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Happy to Help? A systematic review and meta-analysis of the effects of performing acts of kindness on the well-being of the actor

Oliver Scott Curry

University of Oxford

Lee Rowland

University of Bournemouth

Sally Zlotowitz

University College London

John McAlaney

University of Bournemouth

Harvey Whitehouse

University of Oxford

Author Note

Oliver Scott Curry, Institute of Cognitive and Evolutionary Anthropology, University

of Oxford; Lee Rowland, Department of Psychology, University of Bournemouth; Sally

Zlotowitz, Department of Clinical Educational and Health Psychology, University College

London; John McAlaney, Department of Psychology, University of Bournemouth; Harvey

Whitehouse, Institute of Cognitive and Evolutionary Anthropology, University of Oxford

This work on this article was supported by kindness.org. Thanks to Caspar van Lissa

and Rongqin Yu for statistical advice, to Rosalind Arden for useful discussions, to Helena

Cronin for comments on the manuscript, and to Steve Rowland and Emma Seymour for

research assistance.

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Correspondence concerning this article should be addressed to Oliver Scott Curry,

Institute of Cognitive and Evolutionary Anthropology, University of Oxford, 64 Banbury

Road, Oxford, OX2 6PN.

E-mail: oliver.curry@anthro.ox.ac.uk

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Abstract

Does being kind make you happy? Recent advances in the behavioural sciences have

provided a number of explanations of human social, cooperative and altruistic behaviour.

These theories predict that people will be ‘happy to help’ family, friends, community

members, spouses, and even strangers under some conditions. Here we conduct a systematic

review and meta-analysis of the experimental evidence that kindness interventions (for

example, performing ’random acts of kindness’) boost subjective well-being. Our initial

search of the literature identifies 428 articles; of which 19 (21 studies) meet the inclusion

criteria (total N=2,685). We find that the overall effect of kindness on well-being is small-to-

medium (d = 0.36). There is also some indication of publication bias – lower quality studies

tended to find larger effects – suggesting that the true effect size may be smaller still (0.29 ≤

d ≤ 0.33). We recommend that future research: distinguish between the effects of kindness to

specific categories of people; take kindness-specific individual differences into account; and

consider a wider range of distal outcome measures. Such research will advance our

understanding of the causes and consequences of kindness, and help practitioners to

maximise the effectiveness of kindness interventions.

Keywords: kindness, altruism, happiness, well-being, positive psychology

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Happy to Help? A systematic review and meta-analysis of the effects of performing acts

of kindness on the well-being of the actor

Does being kind make you happy? Does doing good make you feel good? Over the

past few decades, advances in the behavioural sciences have developed numerous theories of

human social, cooperative and altruistic behaviour. These theories — kin altruism,

mutualism, reciprocal altruism, and competitive altruism — make it possible to explain a

variety of different ‘kinds of kindness’ (for example, love, sympathy, gratitude and heroism).

And they predict that people will be ‘happy to help’ family, friends, community members,

spouses, and even strangers under some conditions.

More recently, there has been growing interest in using kindness as an intervention to

boost ‘subjective well-being’ (including happiness, life-satisfaction and positive affect). The

idea that, for example, ‘random acts of kindness’ boosts the well-being, happiness and mental

health not only of the recipient, but also the actor has been taken up and promoted by a large

number of research groups and charity organisations (see S1). The idea has even been

explored by the UK government (Aked, Marks, Cordon, & Thompson, 2008; Aked &

Thompson, 2011; Huppert, 2009; Laura Stoll, 2011). It has been argued that altruism —

acting at a cost to benefit others – benefits the altruist as well as the beneficiary. The appeal

of this ‘good news story’ is obvious: if it is true that ‘helping helps the helper’, then

encouraging people to be kind(er) to others could provide a is a simple, effective, inexpensive

and widely-available means of addressing social problems ranging from social isolation to

more serious mental and physical health conditions.

Here we outline existing theories of altruism and their relation to kindness, and

consider the predictions these theories make about well-being. And we conduct a systematic

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review and meta-analysis of previous experimental studies of the effects of kind acts on the

well-being of the actor. We end with a discussion of the limitations of the existing literature,

and make recommendations for future research.

The causes of kindness

Why and under what circumstances are people kind to others? Why do people behave

prosocial, cooperative and altruistic ways? Recent interdisciplinary research has provided a

wealth of answers to these questions. 1

Humans are social animals. Their ancestors have been living in social groups for over

50 million years (Shultz, Opie, & Atkinson, 2011), and for the past 2 million years humans

have been making a living as intensely collaborative hunter-gathers (Tooby & DeVore, 1987).

Social life affords numerous opportunities for mutually beneficial cooperative interactions.

And humans, like other social animals, have been equipped by natural selection with a

variety of traits and dispositions – love, loyalty, benevolence and bravery – that enable them

to seize these opportunities. In addition, the human capacity for culture – the ability to invent

and share new ways of living – has allowed them to build and elaborate upon this benevolent

biological foundation, with rules, norms and other social institutions that further inculcate

and amplify cooperation and altruism (Hammerstein, 2003).

According to game theory – the mathematical analysis of social interaction – there is

not just one type of cooperation, there are many, and hence many different types of social,

cooperative and altruistic behaviour (Curry, 2016; Lehmann & Keller, 2006; Nunn & Lewis,

2001; Sachs, Mueller, Wilcox, & Bull, 2004). These theories make it possible to identify and

explain several different ‘kinds of kindness’.

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People will be kind to their families

Natural selection will favour altruism when the cost to the acting gene is outweighed

by the benefits to copies of that gene that reside in other individuals – that is in genetic

relatives or family members (Dawkins, 1979; Hamilton, 1964). As predicted by this theory of

‘kin selection’, many organisms possess adaptations for detecting and delivering benefits (or

avoiding harm) to kin (Gardner & West, 2014) — the most common example being parental

care of offspring (Clutton-Brock, 1991; Royle, Smiseth, & Kölliker, 2012). Humans have

always lived in groups composed mostly of genetic relatives (Chapais, 2014; Walker, 2014),

and there is evidence to suggest that they too possess adaptations for kin altruism. Humans

detect kin by means of a variety of cues, including maternal perinatal association, co-

residence (Lieberman, Tooby, & Cosmides, 2003, 2007), and possibly phenotype matching

(DeBruine, 2005; Mateo, 2015). A preference for helping kin has been demonstrated in

numerous experiments (Curry, Roberts, & Dunbar, 2013; Madsen et al., 2007). And human

kin altruism is evident in patterns of parental (Geary & Flinn, 2001) and grandparental (Euler

& Weitzel, 1996) investment and its absence (Daly & Wilson, 1996). It has also been argued

that sympathy – a sensitivity to the needs of others – originally evolved to facilitate parental

care (Hublin, 2009; Preston & de Waal, 2002), before becoming available to facilitate other

types of cooperation.

Thus, kin selection can explain kindness in the form of love, care, sympathy and

compassion. And the theory predicts that these tendencies will be elicited by others who

exhibit cues of genetic relatedness, especially vulnerable children. Consistent with this

perspective, research has shown that men are more willing to donate money to children

whose faces have been digitally morphed to resemble their own (Platek, Burch, Panyavin,

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Wasserman, & Gallup Jr, 2002); and people are more generous when donating to charities

using images of children with negative (sad, distressed) as opposed to neutral emotional

expressions (Burt & Strongman, 2005; Small & Verrochi, 2009).

People will be kind to members of their communities

Natural selection will favour altruism to those with whom the actor shares a common

interest – team mates, group members, coalition partners, and others who are ‘in the same

boat’. Game theorists typically model such ‘mutualistic’ interactions as coordination

problems (D. K. Lewis, 1969; Schelling, 1960) – including ‘stag hunts’ (Skyrms, 2004) and

‘soldiers dilemmas’ (Clutton-Brock, 2009). The benefits of ‘working together’ are evident

from the ubiquity in nature of herds, shoals, flocks, and collaborative hunting (Boinski &

Garber, 2000; Boos, Kolbe, Kappeler, & Ellwart, 2011), as well as the formation of alliances

and coalitions (Bissonnette et al., 2015; Harcourt & de Waal, 1992). Coordinating to mutual

advantage has been a recurrent feature of the social lives of humans and their recent

ancestors, especially with regard to collaborative hunting (Alvard, 2001; Alvard & Nolin,

2002), and forming coalitions to compete with rival coalitions (Wrangham, 1999). Humans

have psychological adaptations for detecting coalitions by means of a variety of different

‘badges of membership’ (Kurzban, Tooby, & Cosmides, 2001; McElreath, Boyd, &

Richerson, 2003; Pietraszewski, Curry, Petersen, Cosmides, & Tooby, 2015; Tooby &

Cosmides, 2010); and they spontaneously form, and are altruistic to, their own groups

(sometimes at the expense of other groups) (Balliet, Wu, & De Dreu, 2014; Bernhard,

Fischbacher, & Fehr, 2006; Sherif, Harvey, White, Hood, & Sherif, 1954/1961; Tajfel, 1970).

Coordination to mutual advantage also seems to have spurred the evolution of a sophisticated

‘theory of mind’ – the ability to think about what others are thinking and feeling (Tomasello,

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Carpenter, Call, Behne, & Moll, 2005; Young, Camprodon, Hauser, Pascual-Leone, & Saxe,

2010).

Thus, mutualism (coordination to mutual advantage) can explain kindness in the form

of loyalty, solidarity, camaraderie, civic-mindedness, community spirit, and commitment to a

cause ‘greater than oneself’. And the theory predicts that these tendencies will be elicited by

other members of the groups with which one identifies (including strangers) (Whitehouse &

Lanman, 2014). Consistent with this perspective, research has demonstrated that geographical

proximity (and perhaps perceptions of cultural and genetic similarity) is a major predictor of

the size of U.S. donations to foreign communities affected by large scale natural disasters

(Adams, 1986). Research has also shown that participants primed with words related to

‘connectedness’ (for example, ‘community’, ‘together’, ‘connected’, ‘relationship’) donated

more money to charity (Pavey, Greitemeyer, & Sparks, 2011).

People will be kind to their friends, and others whom they might meet again

Natural selection also favours altruism to those who might return the favour at a later

date (Axelrod, 1984; Trivers, 1971). Under some conditions – modelled by game theorists as

‘prisoner’s dilemmas’ – cooperation can be undermined by ‘cheats’, individuals who accept

the benefit of cooperation without paying the cost. In repeated interactions, a strategy of

‘conditional cooperation’ or ‘reciprocal altruism’ – which initiates and continues cooperation

with cooperators, but which detects and avoids (or punishes) cheats – can overcome this

‘free-rider’ problem (Ostrom & Walker, 2002). Surprisingly, few if any examples of full

blown ‘reciprocal altruism’ have been found in non-human species (Amici et al., 2014;

Clutton-Brock, 2009), although some aspects of reciprocity have been identified in cleaner

fish (Bshary & Grutter, 2006), vampire bats (Carter & Wilkinson, 2013), and primates

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(Mitani, 2009). However, it has been argued that reciprocal social exchange has been a

recurrent feature of the social lives of humans since our last common ancestors with

chimpanzees 6 million years ago (Jaeggi & Gurven, 2013); and there is some suggestive

evidence for trade between human groups from 82,000 years ago (Bouzouggar et al., 2007).

Humans appear to be equipped with adaptations for detecting (Cosmides & Tooby, 2005),

punishing (Price, Cosmides, & Tooby, 2002), and forgiving (McCullough, Kurzban, & Tabak,

2013) ‘cheats’. And reciprocity emerges early in children’s behaviour (Harbaugh, Krause,

Liday, & Vesterlund, 2002), and is used cross-culturally as a strategy for social exchange

(Henrich et al., 2005; Kocher, Cherry, Kroll, Netzer, & Sutter, 2008).

Thus, reciprocal altruism can explain kindness in the form of trust (initiating

cooperation), returning favours, gratitude (for favours yet to be returned), forgiveness and

friendship. The theory can also explain kindness to strangers. An altruistic act may be the

start of a beautiful friendship, a way of making a new friend (after all, ‘a stranger is just a

friend you haven’t met yet’). And in any case, it might be better to ‘err on the side of

caution’, and be altruistic just in case you happen to see the person again (Delton, Krasnow,

Cosmides, & Tooby, 2011; Krasnow, Delton, Tooby, & Cosmides, 2013).

The theory of reciprocal altruism predicts that these tendencies will most likely be

elicited in repeated interactions where individuals expect to meet again, where one’s

cooperative (or uncooperative) behaviour can be observed by others, and towards others who

have helped them in the past, or will be able to help them in the future (Kraft-Todd, Yoeli,

Bhanot, & Rand, 2015). For example, in an experimental game investigating donations made

in public to UNICEF, researchers found that those who gave more money away received

more from their fellow players (Milinski, Semmann, & Krambeck, 2002). And in a test of

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eight different messages designed to increase organ donation, an appeal to ‘reciprocity’ – “If

you needed an organ transplant, would you have one? If so, please help others” – was found

to be the most effective (Harper, 2013; see also: Sanders, Halpern, & Service, 2013, Trial 4).

People will be kind to others when it enhances their status

Natural selection can also favour altruism if it intimidates rivals or impresses potential

mates. Organisms often come into conflict over resources such as food, territory, and mates

(Huntingford & Turner, 1987). Although such conflicts appear purely competitive, in fact

there are costs involved in conflict – time, energy, and injury – that individuals have a

common interest in avoiding. One way of avoiding a damaging fight is for contestants to

display reliable indicators of “fighting ability” (“resource holding power”, or

“formidability”), and for the weaker party to cede the resource to the stronger. In this way, the

stronger party still wins, but both avoid the costs of a real fight (Maynard Smith & Price,

1973). Such ‘ritual contests’ are widespread in nature (C. W. Hardy & Briffa, 2013; Riechert,

1998). In stable social groups, in which relative ‘power’ is already known by reputation

(through direct experience or third-party observation), individuals can dispense with the

contest, and allocate disputed resources by ‘rank’. Such ‘dominance hierarchies’ represent a

further de-escalation of conflict, and are also widespread (Preuschoft & van Schaik, 2000).

Depending on the species, displays of size, weight, age, or experience may carry the day —

but displays of altruism can also work (Gintis, Smith, & Bowles, 2001; Zahavi & Zahavi,

1997). Humans and their recent ancestors have always faced the problem of resolving

conflict, because such problems are inherent in group living (Shultz & Dunbar, 2007). And

all human societies feature status hierarchies, which individuals (especially males) seek to

climb and derive satisfaction from climbing (Anderson, Hildreth, & Howland, 2015;

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Anderson, Kraus, Galinsky, & Keltner, 2012; Mazur, 2005). As predicted, humans –

especially males – commonly engage in costly and conspicuous displays of prowess,

resources, and even altruism (including generosity and bravery), especially in the context of

mate-competition (C. L. Hardy & Van Vugt, 2006; Hawkes, 1991; Hawkes, O'Connell, &

Blurton Jones, 2001; Mazur, 2005; Miller, 2000; Smith & Bleige Bird, 2000). Experiments

suggest that a tendency for the strong to display status by helping the weak – noblesse oblige

– is present cross-culturally (Fiddick, Cummins, Janicki, Lee, & Erlich, 2013).

Thus, ‘competitive altruism’ can explain kindness in the form of generosity, bravery,

heroism, chivalry, magnanimity and public service. This includes acts of kindness to

strangers. Helping a stranger may improve your status (Barclay, 2011; N. J. Raihani &

Bshary, 2015) whether the recipient is in a position to return the favour or not. And the theory

predicts that these tendencies will be elicited in the presence of rivals, or potential mates,

where acting altruistically may enhance one’s status. Consistent with this perspective,

research has shown that male donors give more when donating to an attractive female

fundraiser, especially in response to a large donation made by a competing male (Nichola J.

Raihani & Smith, 2015). (See also: Bereczkei, Birkas, & Kerekes, 2007; Iredale & Van Vugt,

2011).

Thus, multiple theories – kin altruism, mutualism, reciprocal altruism, competitive

altruism – explain multiple types of altruism, and multiple types of kindness. These theories

predict that people will be motivated to be kind to family, friends, colleagues, spouses, and

even strangers under some conditions. These same theories also predict that helping might

make people happy.

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The consequences of kindness

Why would helping make you happy? Broadly speaking, happiness (well-being,

pleasure) can be seen as an internal reward system for acting in ways that promote survival

and reproduction (Buss, 2000). Happiness is: “a psychological reward, an internal signaling

device that tells us that an adaptive problem has been, or is in the process of being, solved

successfully” (Hill, DelPriore, & Major, 2013). From this perspective, it is no problem to

explain why ‘eating’ or ‘having sex’ makes people happy; these behaviours meet important

adaptive goals. And, for the reasons outlined above, it is equally straightforward to explain

why performing acts of kindness might make people happy: it is because caring for family,

maintaining coalitions, trading favours and increasing status are also important adaptive

goals (Schulkin, 2011). Indeed, we might even expect helping others to produce more

happiness than helping yourself: it is precisely because helping others can sometimes give a

better return on investment than helping yourself that evolution has favoured kindness in the

first place.

Thus, the evolutionary behavioural science approach to altruism predicts that people

will be happy to help family, friends, community members, spouses, and even strangers under

some conditions. This prediction has received some support from the existing literature on 2

well-being. A large body of research has established an association between kindness and

happiness and health (Anik, Aknin, Norton, & Dunn, 2009; Konrath & Brown, 2013).

However, much of this research has been correlational — showing, for example, that people

who spend more money on others are happier (Lara B. Aknin et al., 2013), or people who

volunteer to help others are healthier (Jenkinson et al., 2013). While such correlational 3

evidence is consistent with the prediction that people will be happy to help others, it is not

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sufficient to establish a causal relationship between kindness and happiness. After all, it’s

possible that helping makes you happy; but it could also be that happiness makes you helpful,

or it could be that some third variable – health, income, or personality – makes you both

happy and helpful. The distinction between correlation and cause is not a mere philosophical

nicety; it is a genuine difference with important practical implications. In the absence of a

clear causal connection, kindness interventions may not work. They may waste time and

money, or displace other more effective interventions. Worse, they may be counter-

productive. If happiness causes helping (rather than the other way around), then forcing

unhappy people to help may make them less happy still.

In order to establish that performing acts of kindness can cause happiness, what is

needed is experimental research that randomly allocates participants to kindness and non-

kindness conditions, and then measures and compares their subsequent happiness. And so we

undertook a systematic review and meta-analysis of the experimental literature on the effects

of kindness interventions on well-being.

Methods

In order to identify suitable experimental studies of the effects of altruism on the

altruist's well-being, we conducted searches of the scientific databases Web of Science and

PsychInfo for academic articles. The most recent search was conducted on 1st September

2016. The process is summarised in the flow diagram in Figure 1. We used the search string:

(kindness OR altruis* OR prosocial OR co-operat* OR cooperat*) AND (wellbeing OR well-

being OR happiness OR life satisfaction) AND (experiment* OR control OR condition OR

random* OR empirical OR trial) NOT mindfulness OR meditation OR loving-kindness. This

search identified 639 articles. To this we added 19 articles identified by other means

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(following references in books and journal articles, Google scholar searches, viewing

academic researchers’ web-pages). After removing duplicates, we were left with 428 articles.

This initial set of 428 articles was screened. Two researchers (LAR and OSC) read the

titles and abstracts. Subsequently 380 articles were excluded for not meeting the inclusion

criteria. These articles were not experimental (that is, they were qualitative or correlational);

or the kindness-well-being effect was reversed (that is, they looked at whether making people

happy made them kinder, or whether kindness made the recipient happy or healthy); or they

were review papers presenting no new data; or they were on topics not directly relevant to the

current review and in which the effect of kindness on well-being was not measured (for

example, drug-alcohol rehabilitation programmes; kindness in animal husbandry; climate

change and planetary wellbeing; loving-kindness meditation/mindfulness). Cases in which

the researchers disagreed were given greater scrutiny and discussed, and where no consensus

was reached, the articles were included in the next stage of the analysis.

The remaining 48 articles were then read in full, and assessed for appropriateness for

the meta-analysis (see S2 for the full list). This process excluded a further 29 records (and

several studies from included articles) for reasons summarised in Table S1. At the end of this 4

process we were left with 19 articles, containing a total of 21 studies that had experimentally

tested the hypothesis that kindness causes well-being.

For each of these 21 studies we coded the following characteristics:

(a) theory of kindness being tested

(b) mean age of sample

(c) sex of participants

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(d) location of study

(e) type of altruist (for example, whether participants were ‘typically developed

individuals’, as opposed to having been diagnosed with some psychopathology)

(f) type of recipient (for example, whether family, friend, stranger)

(g) the nature of the intervention (for example, ‘random act of kindness’,

prosocial purchase, charitable donation)

(h) size of the intervention group

(i) nature of the control condition (for example, no treatment, self-kindness, other

activity)

(j) size of the control group

(k) dependent measure (for example, well-being, happiness, life-satisfaction)

(l) effect size (Cohen’s d)

When coding studies with multiple (control) groups, and / or multiple dependent

measures, we chose the most appropriate comparison (usually kindness versus neutral) and

the most appropriate measure (usually some measure of happiness).

Results

Study characteristics

The characteristics of the 21 studies are presented in Table 1. These 21 studies

included a total of 2,685 participants (~34% male, mean age ~25.49, SD=12.39). The 5

majority of participants came from Canada, USA and Europe, although there were also

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studies conducted in South Africa, Korea and Vanuatu. Most participants were university

students, although there were also two studies with children, one study of Vanuatu villagers,

and one with elderly participants.

The two most common interventions were ‘acts of kindness’ and ‘prosocial

purchasing’. Typical instructions for the ‘acts of kindness’ intervention were as follows:

“During the coming week, please perform at least five acts of kindness per day and report on them in the evening, including the responses of others that you received. Examples of acts of kindness are: holding a door for someone at university, greeting strangers in the hallway, helping other students in preparing for an exam, etcetera. It does not matter whether you address your acts of kindness to people you know or not” (Ouweneel, Le Blanc, & Schaufeli, 2014).

Prosocial purchasing interventions involved giving participants a sum of money, and

instructing them to spend it on someone else.

Most studies used a self-report measure of subjective well-being, happiness, life-

satisfaction, or positive and negative affect. These included the Subjective Happiness Scale

(SHS; S. Lyubomirsky & Lepper, 1999), the Steen Happiness Index (SHI; Seligman, Steen,

Park, & Peterson, 2005), the Satisfaction With Life Scale (SWLS; Diener, Emmons, Larsen,

& Griffin, 1985), and the Positive Affect and Negative Affect Scale (PANAS; Watson, Clark,

& Tellegen, 1988). Three studies used more objective measures: two used other-rated

smiling, and one used blood pressure.

Scrutiny of the 21 studies identified a number of methodological limitations. In two

studies, participants were not only not blind to the hypothesis, but were explicitly told that

performing acts of kindness would improve their mood (Nelson et al., 2015; Trew & Alden,

2015).

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There was also considerable variation in control conditions. Some studies compared

acting kindly with doing nothing (thus possibly confounding the effects of kindness with the

effects of performing any novel fun activity), whereas others compared acting kindly with

some other similarly interesting activity. (For a direct comparison of these two control

conditions, see: Buchanan & Bardi, 2010).

There was also considerable variation in whether the kindness intervention involved a

cost to the actor. Most ‘acts of kindness’ involved a cost; but, the ‘prosocial spending’ studies

that involved a windfall payment to the participant did not. It was not even clear that

spending the windfall on others even constituted an opportunity cost. In two studies, the

intervention involved either keeping or donating a children’s goody bag (consisting of

chocolate and juice) (Lara B. Aknin et al., 2013; L. B. Aknin, Fleerackers, & Hamlin, 2014).

For the adult participants in the study, keeping a child’s goody bag is presumably not much of

a benefit, and donating it not much of a cost.

We also note that many studies exhibited many ‘researcher degrees of

freedom’ (Simmons, Nelson, & Simonsohn, 2011), through the use of multiple dependent

measures; and that the results across these measures were not always consistent (for example,

the intervention would improve ‘positive affect’ but not ‘life satisfaction’, or vice versa).

Similarly, studies varied in duration, and were able to report results from multiple different

times, not all of which were consistent. For example “The kindness intervention had a

positive influence on both positive emotions and academic engagement, though not in the

long run” (Ouweneel et al., 2014).

However, in the interests of providing as broad an overview of the experimental

literature as possible we erred on the side of including these studies in the meta-analysis.

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Meta-analysis

Meta-analysis was conducted in SPSS V21 and R, following the recommendations

summarised in (Field & Gillett, 2010).

A random-effects model revealed that the mean effect size of the 21 studies was d = .

36, 95% confidence interval (CI) = [.26, .47], Z = 6.71, p < .001 (see Figure 2). This is a

small-to-medium effect, approximately equivalent to an increase of 0.8 on a standard 0-10

happiness scale (Helliwell, Layard, & Sachs, 2016).

A chi-square test of homogeneity of effect sizes was not significant, 2(19) 21.53, p=.

37. These measures suggest considerable similarity in effect sizes across studies. Consistent

with this finding, moderator analysis suggested that the effect of age or sex on the overall

effect size was not significant.

A file-drawer analysis, revealed that 595 unpublished, filed, or unretrieved studies

would be required to bring the significance of this average effect size to nonsignificance.

However, there was evidence of significant publication or reporting bias. Visual

inspection of the Funnel plots (Figure 3) suggests – and Begg's test τ(N = 21) = 0.32, p = 0.04

confirms – that smaller studies tended to find larger effects. This indicates that smaller studies

finding smaller (or negative) effects have not been submitted or published. Adjusting for

severe to moderate one-tailed selection suggests that the true effect size is likely to be 0.29 ≤

d ≤ 0.33 (Vevea & Woods, 2005).

Discussion

The results of this systematic review and meta-analysis of the experimental kindness

literature suggests that performing acts of kindness does improve the well-being of the actor.

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This finding is consistent with the claim that, as social animals, humans possess a range of

psychological mechanisms that motivate them to help others, and that they derive satisfaction

from doing so — in other words, that people are ‘happy to help’ family, friends, community

members, spouses, and even strangers under some conditions.

The effect of these kindness interventions is only small-to-medium (d ≤ 0.36).

However, this effect is comparable to other positive psychology interventions (d=0.34, Bolier

et al., 2013; d=0.31, Sin & Lyubomirsky, 2009; d=0.44, Weiss, Westerhof, & Bohlmeijer,

2016). Furthermore, we should keep in mind that this effect is an aggregate, averaged across 6

individuals and interventions across which theory suggests the effects of kindness

interventions may be very different.

First, theory suggests that some individuals will benefit more than others from

performing acts of kindness – that is, there will be individual differences in the degree to

which individuals derive satisfaction from helping. Like all personality traits (Polderman et

al., 2015), various different types of cooperative behaviours have been found to be

moderately heritable – including in-group favouritism (G. J. Lewis & Bates, 2010), trust

(Cesarini et al., 2008), and fairness (Wallace, Cesarini, Lichtenstein, & Johannesson, 2007).

The satisfaction derived from helping others, and establishing cooperative social relationships

is no exception (Haworth et al., 2016). In addition, there are also obvious situational and

contextual factors that should make a difference. Just as a hungry person derives more

pleasure from eating than a full person, we should expect individuals with a greater need or

desire to establish cooperative relationships to derive more satisfaction from being kind to

others. For example, lonely or isolated people — perhaps those who have moved to a new

city, or a new school — might be happier to seize opportunities to make new friends, or

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connect with their communities, than are people who ‘have enough friends already’ or who

are well-established in their communities. Ambitious people (with more resources to spare)

seeking status may have a greater appetite for, and be happier to seek, opportunities for

conspicuous altruism or public service — “You make a living by what you get; you make a

life by what you give” according to the quote often (mis)attributed to Winston Churchill. 7

Single people who are courting may be happier to help potential mates. Indeed, we might also

expect sex differences, with women happier to help children, and men happier to perform

chivalry or heroics.

However, because none of the studies has systematically varied the type of altruist

(the majority of participants were ‘typical’ although two studies focussed on ‘socially

anxious’ individuals), we do not know whether, for example, lonely people appreciate the

opportunity to reach out to others more than people whose ‘diaries are full’. We do not know

whether single people are happier performing romantic gestures than couples. We do not

know whether men and women are happier performing different types of kindness acts.

And so future research should also investigate whether performing acts of kindness

benefits some types of people more than others. Do people with a greater desire for social

connections benefit from being benevolent more than others? To what extent does sex, age

and income influence the satisfaction derived from acts of kindness? Do personality traits,

and social and moral values, play a mediating role? Do kindness interventions have a greater

effect on some mental health problems than others, perhaps those most related to social

interaction? And are kindness interventions particularly effective with people (re)integrating

into society after being absent from it – recent immigrants, ex-offenders, recovering addicts?

"20

HAPPY TO HELP

Second, theory also suggests that people will be happier to help some people more

than others — for example, family and friends as opposed to anonymous strangers. We note

that, in the present review, some of the studies with the largest effect sizes involved altruism

towards ‘friends and family’ (L. B. Aknin, Broesch, Hamlin, & Van de Vondervoort, 2015; L.

B. Aknin, Dunn, Whillans, Grant, & Norton, 2013; Geenen, Hoheluchter, Langholf, &

Walther, 2014); and other studies have shown that ‘social connection’ with the recipient

increases positive affect in the donor (L. Aknin, Dunn, Sandstrom, & Norton, 2013; L. B.

Aknin, Sandstrom, Dunn, & Norton, 2011). However, the studies reviewed here investigated

the effects of kindness ‘in general’; none systematically varied type of recipient, for example

family, colleague, friend, stranger. In fact, in most cases the recipient was left unspecified –

that is, they could be ‘anyone’. As a consequence, we do not know whether people are

happier giving to family and friends, as opposed to (anonymous) strangers. (And because no

study investigated the effects of acting at a cost to help an (anonymous) stranger, there is no

evidence (either way) on whether helping strangers makes you happy.) We do not know

whether people are happier giving to needy or unlucky recipients, as opposed to affluent or

lazy recipients. We do not know whether people are happier giving to children as opposed to

adults; in-group as opposed to out-groups; females as opposed to males. Thus future work

should seek to fill these gaps in our understanding. There is already a large literature on

whether people behave more or less altruistically to specific types of people; it would be

fairly straightforward to add measures of subjective well-being to replications and extensions

of these designs.

"21

HAPPY TO HELP

With the help of more precise theories regarding which altruists, and which recipients,

benefit most, future research should be able to identify the kind of kindness that works best,

and enable practitioners to ‘put their good where it will do the most’.

To that end, and in order to overcome the limitations of previous research, we make

the following recommendations for future research:

There is no scientific theory that predicts that humans will be selfish under all

conditions. Thus, repeatedly testing the folk intuition that people are selfish, and finding that

they are not, makes no contribution to science. Future research on the effects of kindness on

well-being should instead focus on developing and testing the more fine-grained predictions

of the numerous theories of altruism outlined above. Specifically, future research should

investigate whether the effects of kindness on the happiness of the actor depends on the type

of actor, the type of recipient, and the interaction of these two factors.

Future research could also seek to generalise these findings by employing more

representative community samples (including participants diagnosed with specific mental

health problems) and fewer college students, as well as conducting further cross-cultural

experiments (Henrich, Heine, & Norenzayan, 2010). Such research could harness the

unparalleled data collection opportunities provided by the internet, including on-line

fundraising platforms. And, given the predicted importance of non-anonymous, face-to-face

contact for cooperation and social relations, these internet methods should be combined with

field experiments to further generalise the finding, establish external validity, and pilot actual

interventions.

In addition, given that our meta-analysis suggests that the population effect may be as

low as d = 0.29, in order to detect such an effect with power β = 0.80, future researchers

"22

HAPPY TO HELP

should use a sample size of at least 188 per group (Faul, Erdfelder, Lang, & Buchner, 2007).

We note that only one of the studies reviewed in this meta-analysis met this criteria (average

group size = 64; average β = 0.41), and that such low-powered studies are likely to fail to

detect an effect even if it is there.

Future research could also investigate the effects of different types of altruism on the

recipient which, despite a couple of interesting studies, has yet to be systematically studied

(Baskerville et al., 2000; Pressman, Kraft, & Cross, 2015). For example, are people happier

to be helped by family, and friends as opposed to strangers? By in-group members as

opposed to out-group? Is there any element of shame or resentment at being a ‘charity case’?

Was Orwell right to argue that “A man receiving charity always hates his

benefactor” (Orwell, 1933). To what extent are people suspicious of the motives of altruistic

strangers?

Looking further ahead, future research should also consider the long-term

consequences of acts of kindness. Research on the ‘hedonic treadmill’ suggests that people

might have a hedonic ‘set point’ that they return to whatever happens to them, good or bad

(Ryan & Deci, 2001). So it’s possible that existing outcome measures, which tend to rely on

self-report well-being, are looking for effects in the wrong places (or at the wrong times).

Happiness is a quick hit, which rewards you now for doing things that have long-term

benefits in the future. So, rather than chasing the fleeting effects of happiness, it might be

better to employ or develop measures that assess those long-term benefits. If the function of

altruistic behaviour is to help families, improve communities, make new friends, find a mate,

or increase status, then studies should be measuring these outcomes. Do people allocated to

the kindness condition report better relations with their families? More identification with

"23

HAPPY TO HELP

their communities? More friends? More sexual partners (Arnocky, Piché, Albert, Ouellette, &

Barclay, 2016)? More committed relationships (Kogan et al., 2010)? More resilient

marriages? More recognition and honours? More pride in one’s achievements (Sznycer et al.,

in press)? If so, then future research might be able to finally connect the two types of

happiness — hedonic and eudaemonic — that have hitherto remained apart.

Conclusion

Helping others makes you happy, but the effect is relatively modest. Further empirical

work testing the implications of the many existing theories of social, cooperative and

altruistic behaviour is need to determine whether the effect might be larger for some types of

helpers, when helping some types of recipients. This research will advance our understanding

of the causes and consequences of kindness, and help practitioners to maximise the

effectiveness of kindness interventions.

"24

HAPPY TO HELP

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Endnotes

Rather than attempting to force these diverse theories, mechanisms and processes into a single definition, for 1

the remainder of this paper we will use kindness, altruism, helping, prosociality and related terms interchangeably, to refer broadly to actions that benefit others (at a cost to self), usually accompanied by benevolent subjective emotions.

Given that ‘well-being’ encapsulates a range of states and associated behaviours (OECD, 2013), and is 2

generally "measured by simply asking people about their happiness” (Dolan & Metcalfe, 2012), for the remainder of this paper we will use well-being, happiness, life-satisfaction and related terms interchangeably.

Even then the effects are modest. This meta-analysis of the relationship between volunteering and health in the 3

elderly found that volunteers were 22% less likely that non-volunteers to die during the follow-up period of the studies (Jenkinson et al., 2013). However, the import of this finding depends on the base-rate. By way of illustration, if on average 10 out of 1000 (1%) non-volunteers die during the follow-up period, then a 22% percent decrease means that 7.8 out of 1000 (0.78%) volunteers would die during the same period. Moreover, as this review goes on to say: “These findings were not confirmed by experimental studies.”

The most highly cited paper in the kindness literature (with 597 citations at the time of the last search) purports 4

to provide evidence that kind acts boosts the well-being of the actor (Sonja Lyubomirsky, Sheldon, & Schkade, 2005). However, the article does not report the size of the sample, the dependent measure, or any inferential statistics (for example, effect size or significance). Email correspondence with the author revealed that the data are no longer available.

These averages are approximate (~), because the age and sex ratio of the samples were not available for some 5

studies.

Although see Coyne (2014a, 2014b) for critical commentary on (Sin & Lyubomirsky, 2009) and (Bolier et al., 6

2013).

Quotes Falsely Attributed to Winston Churchill: http://www.winstonchurchill.org/resources/quotations/135-7

quotes-falsely-attributed.

"44

Tabl

e 1

Mai

n ch

arac

teri

stic

s of

stu

dies

incl

uded

in th

e m

eta-

anal

ysis

Stud

yT

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(201

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3821

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(201

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swee

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200.

30

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l. (2

013)

Stud

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Pros

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l34

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70

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(201

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6059

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kid

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ther

resu

lts n

s. Th

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party

rate

d pr

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with

gre

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hap

pine

ss

d=0.

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l. (2

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46

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w (2

013)

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2819

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3843

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010)

No

theo

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cal

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one

LS28

280.

21

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008)

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67

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014)

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(201

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ccep

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ena

10.6

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KW

here

abou

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138

138

0.16

Mar

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, & R

yan

(201

6)Pr

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A

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mou

s / S

DT

3620

.40

naTy

pica

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enev

olen

ceN

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3442

0.55

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cost

; fre

eric

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m

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grai

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et a

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011)

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/ SI

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3C

anad

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AK

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ory

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229

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as n

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r ‘an

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la P

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015)

US

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1U

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WB

5252

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anip

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Nel

son,

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la P

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5757

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Nel

son,

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l. (2

016)

Pros

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l40

29.9

5U

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lfO

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118

0.29

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clud

ed N

eutra

l con

trol.

O'C

onne

ll, O

'She

a, e

t al.

(201

6)PP

A/S

ocia

l Sup

port

~54

~34.

17U

SATy

pica

lA

KSe

lfSo

cial

N

etw

ork

SHS

2831

0.33

Als

o in

clud

ed N

eutra

l con

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Sign

ifica

nt e

ffect

s on

oth

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utco

me

(RS)

.

Ouw

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t al.

(201

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2Po

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ycho

logy

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cade

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1620

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Net

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Typi

cal

AK

Neu

tral

Act

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Any

one

SR-P

(N)E

2524

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“The

kin

dnes

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ntio

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d a

posi

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influ

ence

…th

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in th

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Trew

, & A

lden

(201

5)So

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Avo

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7C

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Ex

posu

reA

nyon

ePA

3841

0.00

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clud

ed ‘L

ife D

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ls’,

cont

rol c

ondi

tion.

Pa

rtici

pant

s in

treat

men

t con

ditio

n “w

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info

rmed

th

at a

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f kin

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Whi

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(201

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5072

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pres

sure

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= sa

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=Dep

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atis

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ositi

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Psyc

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gica

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; RS=

Rel

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nshi

p Sa

tisfa

ctio

n; S

=Stu

dy; S

A=S

ocia

l A

nxie

ty; S

HI=

Stee

n H

appi

ness

Inde

x; S

HS=

Subj

ectiv

e H

appi

ness

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le ;

SIT=

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terd

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denc

e Th

eory

; SR

-P(N

)E=S

elf-

repo

rt Po

sitiv

e an

d (N

egat

ive)

Em

otio

ns; U

G=U

nder

grad

uate

; WB

=Wel

l-bei

ng.

Figure 1: Flow diagram of the search and selection procedure of studies

Full-text articles excluded (n = 29)

1) No kind acts, just recall n=3

2) Counting kind acts, no new ones n=4

3) Expected or imaginary kindness n=3

4) No control n=25) Comparing kindness on

other IV n=46) Kind acts embedded

with other positive activities n=6

7) Incomplete description of experiment n=1

8) Review or meta-analysis n=3

9) Correlational n=3

Records after duplicates removed (n = 428)

Studies included in quantitative synthesis

(meta-analysis)(n = 21)

Full-text articles assessed for eligibility

(n = 48)

Records excluded (n = 380)

Records screened (n = 376)

Additional records identified through other sources

(n = 19)

Identification

Eligibility

Included

Screening

Records identified through database searching

(n = 639)

Figure 2: Forest plot for the effect of kindness acts on actor’s well-being

OVERALL

-0.5 0 0.5 1 1.5 2

Effect Size (d)

Whillans Dunn et al. (2016; S2)Trew & Alden (2015)Ouweneel Le Blanc et al. (2014; S2)O'Connell O'Shea et al. (2016)Nelson Layous et al. (2016)Nelson Della Porta et al. (2015; USA)Nelson Della Porta et al. (2015; Korea)Mongrain Chin et al. (2011)Martela & Ryan (2016)Layous Nelson et al. (2012)Layous Lee et al. (2013)Geenen Hoheluchter et al. (2014)Dunn Aknin et al. (2008; S3)Buchanan & Bardi (2010)Alden & Trew (2013)Aknin Hamlin et al. (2012)Aknin Fleerackers et al. (2014)Aknin Dunn et al. (2013; S3)Aknin Broesch et al. (2015; S2)Aknin Broesch et al. (2015; S1)Aknin Barrington-Leigh et al. (2013; S3)

0.19 [-0.26, 0.64] 0.00 [-0.45, 0.45] 0.97 [ 0.38, 1.56] 0.33 [-0.18, 0.84] 0.29 [ 0.07, 0.51] 0.82 [ 0.43, 1.21]-0.10 [-0.49, 0.29] 0.31 [ 0.13, 0.49] 0.55 [ 0.10, 1.00] 0.16 [-0.08, 0.40] 0.18 [-0.06, 0.42] 0.70 [ 0.21, 1.19] 0.67 [ 0.08, 1.26] 0.21 [-0.32, 0.74] 0.50 [ 0.05, 0.95] 0.46 [-0.17, 1.09] 0.38 [ 0.03, 0.73] 0.70 [ 0.03, 1.37] 0.30 [-0.33, 0.93] 0.93 [ 0.13, 1.73] 0.46 [ 0.19, 0.73]

0.36 [ 0.26, 0.47]

Figure 3: Funnel plot for the effect of acts of kindness on actor’s well-being

Effect Size (d)

Sta

ndar

d E

rror

0.41

0.307

0.205

0.102

0

-0.5 0 0.5 1

Supplementary Material for ‘Happy to Help”?

S1: Organisations working on kindness and happiness

Ark Project Now (ARK) started with a simple question: “What if kindness became normal?” http://www.arkprojectnow.com Be Kind to Human Kind aims to celebrate people and their kind acts and is a platform to share positive news, stories, photos, videos, poems and quotes. http://bk2hk.org/about/ Happify defines itself as “the single [online] destination for effective, evidence-based solutions for emotional health and well-being in the 21st century.” http://www.happify.com Life Vest Inside is a “non-profit organization dedicated to empowering the masses to engage in acts of love and kindness.” http://www.lifevestinside.com Random Acts is “committed to creating a network of kindness through strategic partnerships with organizations from around the world.” http://www.randomacts.org Random Acts of Kindness (RAK) is a foundation that encourages the spread of kindness in schools, communities and homes. https://www.randomactsofkindness.org SpreadKindness is a “non-profit organization dedicated to encouraging and empowering people to practice kindness in their everyday lives. We provide individuals and groups with tools, ideas, projects and events that help make the world a kinder place.” http://www.spreadkindness.org The Sugar Cube Factory is a website that helps people to distribute (digitally) their words of kindness around the world. http://www.sugarcubefactory.com The Cambridge Prosociality and Well-being Lab at the University of Cambridge investigates “the psychology and biology of human kindness and well-being.” http://cpwlab.azurewebsites.net/Welcome.aspx The Center for Compassion and Altruism Research and Education, Stanford School of Medicine (CCARE) investigates methods for cultivating compassion and promoting altruism within individuals and society http://ccare.stanford.edu The Greater Good Science Center (GGSC) at the University of California, Berkeley “studies the psychology, sociology, and neuroscience of well-being, and teaches skills that foster a thriving, resilient and compassionate society.”

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http://greatergood.berkeley.edu/about The Institute for Research on Unlimited Love seeks to “increase public awareness of…(1) new scientific investigations…; (2) insights of the world’s great philosophical, spiritual and theological traditions; and (3) inspiring works of love by exemplars across the world.” http://unlimitedloveinstitute.org/about.php

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S2: List of 48 reviewed articles (* = included in meta-analysis)

Aknin, L., Dunn, E., Sandstrom, G., & Norton, M. (2013). Does social connection turn good deeds into good feelings?

*Aknin, L. B., Barrington-Leigh, C. P., Dunn, E. W., Helliwell, J. F., Burns, J., Biswas-Diener, R., . . . Norton, M. I. (2013). Prosocial spending and well-being: Cross-cultural evidence for a psychological universal. Journal of Personality and Social Psychology, 104(4), 635-652. doi:10.1037/a0031578 10.1037/a0031578.supp (Supplemental)

*Aknin, L. B., Broesch, T., Hamlin, J. K., & Van de Vondervoort, J. W. (2015). Prosocial behavior leads to happiness in a small-scale rural society. Journal of Experimental Psychology: General, 144(4), 788-795. doi:10.1037/xge0000082

*Aknin, L. B., Dunn, E. W., & Norton, M. I. (2012). Happiness runs in a circular motion: Evidence for a positive feedback loop between prosocial spending and happiness. Journal of Happiness Studies, 13(2), 347-355. doi:10.1007/s10902-011-9267-5

Aknin, L. B., Dunn, E. W., Whillans, A. V., Grant, A. M., & Norton, M. I. (2013). Making a difference matters: Impact unlocks the emotional benefits of prosocial spending. Journal of Economic Behavior & Organization, 88, 90-95. doi:10.1016/j.jebo.2013.01.008

*Aknin, L. B., Fleerackers, A. L., & Hamlin, J. K. (2014). Can third-party observers detect the emotional rewards of generous spending? Journal of Positive Psychology, 9(3), 198-203. doi:10.1080/17439760.2014.888578

*Aknin, L. B., Hamlin, J. K., & Dunn, E. W. (2012). Giving leads to happiness in young children. PLoS ONE, 7(6). doi:10.1371/journal.pone.0039211

Aknin, L. B., Sandstrom, G. M., Dunn, E. W., & Norton, M. I. (2011). It’s the recipient that counts: Spending money on strong social ties leads to greater happiness than spending on weak social ties. PLoS ONE, 6(2). doi:10.1371/journal.pone.0017018

Aknin, L. B., Van Boven, L., & Johnson-Graham, L. (2015). Abstract construals make the emotional rewards of prosocial behavior more salient. The Journal of Positive Psychology, 10(5), 458-462. doi:10.1080/17439760.2014.967801

*Alden, L. E., & Trew, J. L. (2013). If it makes you happy: Engaging in kind acts increases positive affect in socially anxious individuals. Emotion, 13(1), 64-75. doi:10.1037/a0027761

*Buchanan, K. E., & Bardi, A. (2010). Acts of Kindness and Acts of Novelty Affect Life Satisfaction. Journal of Social Psychology, 150(3), 235-237.

Chancellor, J., Layous, K., & Lyubomirsky, S. (2015). Recalling positive events at work makes employees feel happier, move more, but interact less: A 6-week randomized controlled intervention at a Japanese workplace. Journal of Happiness Studies, 16(4), 871-887. doi:10.1007/s10902-014-9538-z

Drozd, F., Mork, L., Nielsen, B., Raeder, S., & Bjorkli, C. A. (2014). Better Days - A randomized controlled trial of an internet-based positive psychology intervention. Journal of Positive Psychology, 9(5), 377-388. doi:10.1080/17439760.2014.910822

*Dunn, E. W., Aknin, L. B., & Norton, M. I. (2008). Spending money on others promotes happiness. Science, 319(5870), 1687-1688. doi:10.1126/science.1150952

Gander, F., Proyer, R. T., Ruch, W., & Wyss, T. (2013). Strength-based positive interventions: Further evidence for their potential in enhancing well-being and alleviating depression. Journal of Happiness Studies, 14(4), 1241-1259. doi:10.1007/s10902-012-9380-0

*Geenen, N. Y. R., Hohelüchter, M., Langholf, V., & Walther, E. (2014). The beneficial effects of prosocial spending on happiness: Work hard, make money, and spend it on others? The Journal of Positive Psychology, 9(3), 204-208. doi:10.1080/17439760.2014.891154

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Haworth, C. M. A., Nelson, S. K., Layous, K., Carter, K., Bao, K. J., Lyubomirsky, S., & Plomin, R. (2016). Stability and Change in Genetic and Environmental Influences on Well-Being in Response to an Intervention. PLoS ONE, 11(5). doi:10.1371/journal.pone.0155538

Huang, Y. H. (2016). Downward Social Comparison Increases Life-Satisfaction in the Giving and Volunteering Context. Social Indicators Research, 125(2), 665-676. doi:10.1007/s11205-014-0849-6

Kerr, S. L., O'Donovan, A., & Pepping, C. A. (2015). Can Gratitude and Kindness Interventions Enhance Well-Being in a Clinical Sample? Journal of Happiness Studies, 16(1), 17-36. doi:10.1007/s10902-013-9492-1

*Layous, K., Lee, H., Choi, I., & Lyubomirsky, S. (2013). Culture matters when designing a successful happiness-increasing activity: A comparison of the United States and South Korea. Journal of Cross-Cultural Psychology, 44(8), 1294-1303. doi:10.1177/0022022113487591

Layous, K., Nelson, Kurtz, & Lyubomirsky. (2016). What triggers prosocial effort? A positive feedback loop between positive activities, kindness, and well-being.

*Layous, K., Nelson, S. K., Oberle, E., Schonert-Reichl, K. A., & Lyubomirsky, S. (2012). Kindness Counts: Prompting Prosocial Behavior in Preadolescents Boosts Peer Acceptance and Well-Being. PLoS ONE, 7(12). doi:10.1371/journal.pone.0051380

Liu, W., & Aaker, J. (2008). The happiness of giving: The time-ask effect. Journal of Consumer Research, 35(3), 543-557. doi:10.1086/588699

Lyubomirsky, S., & Layous, K. (2013). How do simple positive activities increase well-being? Current Directions in Psychological Science, 22(1), 57-62. doi:10.1177/0963721412469809

Lyubomirsky, S., Sheldon, K. M., & Schkade, D. (2005). Pursuing happiness: The architecture of sustainable change. Review of General Psychology, 9(2), 111-131. doi:10.1037/1089-2680.9.2.111

*Martela, F., & Ryan, R. M. (2016). Prosocial behavior increases well-being and vitality even without contact with the beneficiary: Causal and behavioral evidence. Motivation and Emotion, 40(3), 351-357. doi:10.1007/s11031-016-9552-z

McNulty, J. K., & Fincham, F. D. (2012). Beyond positive psychology? Toward a contextual view of psychological processes and well-being. American Psychologist, 67(2), 101-110. doi:10.1037/a0024572

Meier, S., & Stutzer, A. (2008). Is Volunteering Rewarding in Itself? Economica, 75(297), 39-59. doi:10.1111/j.1468-0335.2007.00597.x

*Mongrain, M., Chin, J. M., & Shapira, L. B. (2011). Practicing Compassion Increases Happiness and Self-Esteem. Journal of Happiness Studies, 12(6), 963-981. doi:10.1007/s10902-010-9239-1

*Nelson, S. K., Della Porta, M. D., Bao, K. J., Lee, H. C., Choi, I., & Lyubomirsky, S. (2015). ‘It’s up to you’: Experimentally manipulated autonomy support for prosocial behavior improves well-being in two cultures over six weeks. The Journal of Positive Psychology, 10(5), 463-476. doi:10.1080/17439760.2014.983959

Nelson, S. K., Layous, K., Cole, S. W., & Lyubomirsky, S. (2016). Do Unto Others or Treat Yourself? The Effects of Prosocial and Self-Focused Behavior on Psychological Flourishing. Emotion. doi:10.1037/emo0000178 10.1037/emo0000178.supp (Supplemental)

Ng, W. (2016). Use of positive interventions: Does neuroticism moderate the sustainability of their effects on happiness? The Journal of Positive Psychology, 11(1), 51-61. doi:10.1080/17439760.2015.1025419

*O’Connell, B. H., O’Shea, D., & Gallagher, S. (2016). Enhancing social relationships through positive psychology activities: A randomised controlled trial. The Journal of Positive Psychology, 11(2), 149-162. doi:10.1080/17439760.2015.1037860

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Otake, K., Shimai, S., Tanaka-Matsumi, J., Otsui, K., & Fredrickson, B. L. (2006). Happy people become happier through kindness: A counting kindnesses intervention. Journal of Happiness Studies, 7(3), 361-375. doi:10.1007/s10902-005-3650-z

*Ouweneel, E., Le Blanc, P. M., & Schaufeli, W. B. (2014). On being grateful and kind: Results of two randomized controlled trials on study-related emotions and academic engagement. The Journal of Psychology: Interdisciplinary and Applied, 148(1), 37-60. doi:10.1080/00223980.2012.742854

Poulin, M. J., Brown, S. L., Dillard, A. J., & Smith, D. M. (2013). Giving to Others and the Association Between Stress and Mortality. American Journal of Public Health, 103(9), 1649-1655. doi:10.2105/Ajph.2012.300876

Pressman, S. D., Kraft, T. L., & Cross, M. P. (2015). It’s good to do good and receive good: The impact of a ‘pay it forward’ style kindness intervention on giver and receiver well-being. The Journal of Positive Psychology, 10(4), 293-302. doi:10.1080/17439760.2014.965269

Proctor, C., Maltby, J., & Linley, P. A. (2011). Strengths use as a predictor of well-being and health-related quality of life. Journal of Happiness Studies, 12(1), 153-169. doi:10.1007/s10902-009-9181-2

Raposa, E. B., Laws, H. B., & Ansell, E. B. (2016). Prosocial Behavior Mitigates the Negative Effects of Stress in Everyday Life. Clinical psychological science : a journal of the Association for Psychological Science, 4(4), 691-698. doi:10.1177/2167702615611073

Reyniers, D., & Bhalla, R. (2013). Reluctant altruism and peer pressure in charitable giving. Judgment and Decision Making, 8(1), 7-15.

Rudd, M., Aaker, J., & Norton, M. I. (2014). Getting the most out of giving: Concretely framing a prosocial goal maximizes happiness. Journal of Experimental Social Psychology, 54, 11-24. doi:10.1016/j.jesp.2014.04.002

Schwartz, C. E., & Sendor, R. M. (1999). Helping others helps oneself: response shift effects in peer support. Social Science & Medicine, 48(11), 1563-1575. doi:10.1016/s0277-9536(99)00049-0

Sin, N. L., & Lyubomirsky, S. (2009). Enhancing well-being and alleviating depressive symptoms with positive psychology interventions: a practice-friendly meta-analysis. Journal of Clinical Psychology, 65(5), 467-487. doi:10.1002/jclp.20593

*Trew, J. L., & Alden, L. E. (2015). Kindness reduces avoidance goals in socially anxious individuals. Motivation and Emotion, 39(6), 892-907. doi:10.1007/s11031-015-9499-5

Weinstein, N., DeHaan, C. R., & Ryan, R. M. (2010). Attributing autonomous versus introjected motivation to helpers and the recipient experience: Effects on gratitude, attitudes, and well-being. Motivation and Emotion, 34(4), 418-431. doi:10.1007/s11031-010-9183-8

Weinstein, N., & Ryan, R. M. (2010). When helping helps: Autonomous motivation for prosocial behavior and its influence on well-being for the helper and recipient. Journal of Personality and Social Psychology, 98(2), 222-244. doi:10.1037/a0016984

Weiss, L. A., Westerhof, G. J., & Bohlmeijer, E. T. (2016). Can We Increase Psychological Well-Being? The Effects of Interventions on Psychological Well-Being: A Meta-Analysis of Randomized Controlled Trials. PLoS ONE, 11(6), e0158092. doi:10.1371/journal.pone.0158092

*Whillans, A. V., Dunn, E. W., Sandstrom, G. M., Dickerson, S. S., & Madden, K. M. (2016). Is spending money on others good for your heart? Health Psychology, 35(6), 574-583. doi:10.1037/hea0000332

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Table S1

Reasons for excluding studies from final 48

Reason for Exculsion Studies Excluded

Use of kindness recall rather than acts of kindness

Aknin, Barrington-Leigh et al., Study 2a/b; Aknin, Dunn, & Norton, 2012; Aknin et al, 2013, Study 2; Aknin et al., 2011

Counting acts of kindness, but no new ones instigated

Gander et al., 2013; Kerr et al., 2015; Ng, 2016; Otake, 2006

Use of expected or imaginary kindness Aknin et al., 2015; Huang, 2016; Weinstein et al., 2010

No control group Pressman et al., 2015; Rudd et al., 2014

Comparing two kindness groups on a different I.V.

Social connection: Aknin et al 2013. Impact: Aknin et al, 2013, Study 1. Intentions: Liu & Aaker, 2008; Peer pressure: Reyniers & Bhalla, 2013. Autonomy: Weinstein & Ryan, 2010

Including acts of kindness with other positive activity interventions, i.e. no direct test of kindness

Chancellor, et al., 2015; Drozd et al., 2014; Haworth, et al., 2016; Layous et al., 2016; Meier & Stutzer, 2008; Schwartz & Sendor, 1999

Incomplete description of experimental details

Lyubomirsky et al., 2005

Review or meta-analysisLyubomirsky & Layous, 2013; McNulty, 2012; Sin & Lyubomirsky, 2009

Correlational studiesAknin, Barrington-Leigh, et al., Study 1; Dunn, et al., 2008, Study 1 & 2; Huang, 2016; Poulin et al, 2013; Proctor, 2011; Raposa, 2016