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Birth order and intelligence 1
CHAPTER I
INTRODUCTION
Does our birth order really affect intelligence? Much research has been revolving around
this question. This issue has once again risen in popularity in the recent years. Debates on the
relationship between birth order and intelligence are surrounded by ambiguity and controversies.
There are countless reports of argument regarding this issue. Some believe that the older
sibling has the upper hand (Kristensen & Bjerkedal, 2007); where else others deem the youngest
to be brighter (Carey, 2007). Yet, others have found no relationship between birth order and
intelligence (MacCallum et. al., 2007).
As this study has yet to be conducted in Malaysia, curiosity regarding the pattern of birth
order and intelligence has arose. Due to the different cultural background of previous research,
the results from abroad may not be applicable to the Malaysian context.
The influence of the Asian and Western culture may cause deviations on the basis of
intelligence (Arthur, n. s.). This is supported by a research saying that Asians, when compared to
Westerners, are able to obtain 5 to 10 points higher than the Caucasians and African Americans
(Arthur, n. s.). There are also different perspectives in defining the roots of intelligence, where
Westerners believe that intelligence is an in-born trait, contrasting to the Asians who consider
intelligence as a result of hard work (Arthur, n. s.).
Literature Review
Birth order. Have you ever looked at another sibling and thought what it would be like
if we were them? Why is it that they differ so much from us? Would life be different for us? The
probability is uncertain and it is difficult for us to determine. Birth order is one of the many
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things that affect the way we carry ourselves and how we interact with our surroundings (Leman,
2005).
Birth order is the rank or order of a person by age among his or her siblings (Reber &
Reber, 2001). It refers to the position in which we are placed in our family whereby we could be
the first child, middle child or even the youngest child (Leman, 1985).
Several research think that the way we mature is highly influenced by where we are in a
relationship with our siblings (Leman, 1985). According to Leman (1985), birth order is a way in
which we can acquire some clues as to why we are the way we are, although it may not
accurately predict how a person would turn out. To sum up Leman’s (1985) points, he said that a
person’s order of birth has a lifelong effect on whom and what a person turns out to be.
A columnist, Brockenbrough (2007), states that birth order is the idea that our position in
the family has influence on which who we are – composing of our personality traits to the overall
intelligence. Some people give credit to birth order as they did to astrology, leading to sibling
rivalry (Brockenbrough, 2007).
How do people remember their birth order? A scientific study done on the fruit fly,
drosophila, can illustrate the resemblance to the functioning of the human brain. In this research,
it is found that the brain cells function in a sequence of transcribing feature activation allowing
the neuroblasts to give rise to a series of different daughter cells (Doe, 2001). Initially, this brain
patterns were found in the fruit fly, drosophila. The daughter cells then ultimately become
neurons and glial cells in the brain (Doe, 2001).
Scientists have also found that the daughter cells carry on producing the particular
transcription factor that was active in the neuroblast at the time of birth (Doe, 2001). It is a
memory that allows neurons to maintain differences based on their time of birth (Doe, 2001). As
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an example, the first-born drosophila neurons usually make the longest axon projections to
remote targets as compared to later-born drosophila that usually makes a shorter axon projection.
This connection between the brain functioning of the fruit fly and the human brain is hypotheses
to be rather similar.
Alfred Adler (1870 – 1937), an Austrian psychiatrist who was the pioneer researcher of
birth order, proposed that the chronological order of siblings at birth or their position in the
family has a substantial influence on the child’s development as well as personality (Stein, n.s.).
He was the first theorist to include not only both the child’s parents and surrounding adults, but
also the child’s brothers and sisters (Boeree, 2006). From the Adlerian point of view, birth order
is merely one of five major influences on personality development.
Besides birth order, it also includes physical structure and appearance, shaping education,
social and economic status and gender roles (Stein, n.s.). Adler’s theory of birth order is
considered one of the useful theories that contribute to the understanding of the order of birth but
at the same time, it should not be taken too seriously (Boeree, 2006).
Results of past research on birth order vary from one another, therefore making it a
controversial subject which is still all together interesting. Based on the initial research done by
Adler, birth order has been linked to various situations by present-day experts and analysts. The
personality aspect is widely researched on compared to the other portions such as intelligence,
career choice, sexual orientation and also cancer risk (Needlman, 2001). Examining the family
structure carefully is crucial as the birth order can reveal many things in a child (Needlman,
2001). With the many factors that influence the birth order, this study solely focuses on how
intelligence is linked to the birth order.
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Intelligence. Intelligence is an abstract word which is much easier described than
defined. It is often referring to other’s intelligence by unfolding people as smart, sharp, bright,
brilliant and many more (Baron & Kalsher, 2002). The American Psychological Association
(APA) has defined intelligence as the “ability to understand complex ideas, to adapt effectively
to the environment, to learn from experience, to engage in various forms of reasoning, and to
overcome obstacles by taking thought” (Wood, Wood & Boyd, 2004).
The ability to learn about, learn from, understand, and interact with one’s environment is
termed as intelligence (Bainbridge, 2007). This ability includes a number of specific abilities
such as adaptability to a new environment, capacity for knowledge and the ability to acquire it,
capacity for reasoning and abstract thinking, skill to grasp relationships, aptitude in evaluating
and judging and the capacity for productive thinking (Bainbridge, 2007). All these abilities and
more, mainly circles around the abilities of a person to learn and interrelate with the environment
(Bainbridge, 2007).
Charles Spearman, in the early 20th century, proposed the existence of general
intelligence, observed that people’s scores on different IQ tests tends to correlate. Therefore, he
concluded that all IQ tests measures the same factor which is the general-factor (Roulinski,
2007). The general-factor includes all logical tasks and mental capacities (Sternberg, 2006).
Apart from that, a similar theory by R. Cattell and J. Horn, argues that there are two types of
intelligence which is the fluid and crystallized intelligence (Roulinski, 2007). Fluid intelligence
is the biological ability to reason and acquire new information as compared to the crystallized
intelligence which is learned through experience and exposure (Roulinski, 2007).
Some theorists proposed that there are different types of intelligence instead of
unearthing the essentials of intelligence. Robert Sternberg’s triarchic theory of intelligence is
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more widely known, than the theory of multiple intelligence proposed by Gardner (Wood, Wood
& Boyd, 2004).
Sternberg’s theory as its name implies, consists of three separate, though interrelated
abilities, namely analytical intelligence, creative intelligence and practical intelligence (Wilson,
2005). The first capacity, analytical or componential intelligence, is referred more as the
traditional conception of intelligence, whereby it looks mostly into abstract thought and
reasoning as well as verbal and mathematical skills (Huitt, 1999). Individuals who have
analytical intelligence are basically high achievers in class (Hetherington E. M., Parke R. D.,
Gauvain M. & Locke V. O., 2006)
Next, would be the experiential or creative intelligence, which is characterized by an
individuals’ ability to generate new ideas, handle unique situations and also to think innovatively
(Huitt, 1999). The final capability proposed by Sternberg is the contextual or practical
intelligence (Huitt, 1999). This refers to the street smart individuals that have the ability to apply
their knowledge in the real world situation (Huitt, 1999).
In the multiple intelligence approach as proposed by Gardner, there are nine types of
intelligence which are the naturalist, musical, logical-mathematical, existential, interpersonal,
bodily-kinesthetic, linguistic, intra-personal and spatial intelligence (Gardner, n.s). The naturalist
intelligence or nature smarts are able to discriminate among living things as well as are sensitive
to other features of the world (Gardner, n.s).
As for the musical intelligence, it enables us to distinguish, craft, reproduce, and reflect
on music. Mathematical and musical intelligences may share the common cognitive processes.
People with logical-mathematical intelligence have the ability to calculate, compute, use abstract
symbolic thought, sequential reasoning skills and carry out complete mathematical operations
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(Gardner, n.s). Next, is the existential intelligence where these people have the sensitivity and
capability to tackle mysterious questions about human existence (Gardner, n.s).
Interpersonal intelligence or better known as people smart, are capable of understanding
and interacting effectively with others. As for the ability to maneuver objects and use a variety of
physical skills with good body-mind coordination is referred to as the bodily-kinesthetic
intelligence (Gardner, n.s). Besides that, the linguistic intelligence is the talent to think in words
and express complex meanings using language (Gardner, n.s).
Intra-personal intelligence on the other hand, is the capability to understand oneself and
one’s thoughts and feelings, and using that knowledge in determining and planning the direction
of their lives (Gardner, n.s). Lastly, the spatial intelligence is the ability to think in three
dimensional forms, where it involves mental imagery, graphic and artistic skills and an active
imagination (Gardner, n.s).
There are a few ways of measuring intelligence. Psychometric approach are based on
how well people perform on standardize aptitude tests. These tests are used to measure skills and
knowledge gathered (Wade & Tavris, 2002). The psychometric test that is extensively used in
measuring intelligence is the Stanford-Binet Intelligence test which was devised in 1904 (Wade
& Tavris, 2002). Later on, others developed a scoring system by using the child’s mental age
divided by the child’s chronological age. This results in the intelligence quotient, also known as
IQ (Baron & Kalsher, 2002). IQ is attained by using the mental age divided by the chronological
age, then multiplied by 100 (Baron & Kalsher, 2002).
From these psychometric tests, many researchers regarding intelligence have been able to
use these measurements as a comparison and guide point. Intelligence has been involved in
research on several areas such as birth order, brain functioning and lots more.
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Birth order and intelligence. This research has yielded contradicting results whereby
some state that the birth order affects a person’s intelligence as well as the other extreme of no
such overlap between intelligence and birth order. Rodgers, Cleveland, Van den Oord, and Rowe
(2000) believe that the connection between intelligence and birth order is merely a
“methodological illusion” due to the variation in results from the different methods used (Evans
& McClintic, 2002).
Zojonc (2001) who believes that birth order does impact a person’s intelligence
developed the confluence model. This model shows that each successive sibling is born into a
weaker intellectual surrounding and that intellectual accomplishment is amplified as family size
decreases (Evans & McClintic, 2002). But the studies only show a tiny advantage in first-born -
about one IQ point higher than the second sibling, two points higher than the third sibling, and so
on. These minor differences are not likely to matter in the quest of distinction (Sulloway, 1996).
The outcomes differ from each other as in the study done by Steckel (1930), where he
concluded that the average intelligence of later-born children was higher than the older children
and that intelligence increases with the ordinal number of a family (Walton, 2001). This is
because parents tend to prefer last-born children, thus, increasing the time spent together and
leading to enhancing intelligence (Walton, 2001).
Opposing this idea was the study completed by Burton (1967) stating that oldest siblings
tend to have higher intelligence than younger siblings (Walton, 2001).
Apart from that, a recent study has shown that birth order does not have any effects on
intelligence. Wichman A. (2006), stated that, “Birth order may appear to be associated with
intelligence, but that's only because larger families don't have the advantages of smaller families.
When examined within families, there is no evidence of any significant association between birth
Birth order and intelligence 8
order and intelligence. Birth order is not all that important compared to family environment and
genetic influences (ScienceDaily, 2007). He pointed out that the mother’s age at the birth of the
first child plays a great role in determining the expected intelligence scores (Wichman, 2006).
The younger a mother was at the delivery of her first infant, the lower the intelligence scores are
projected to be within a family (Wichman, 2006).
Why it is that birth order might affect intelligence? As the first-born, they would be more
likely to have financial resources to continue education, being treated as a companion by parents
(therefore, having more responsibility) and would get significantly more attention and
nourishment compared to the following siblings (Galton, 1874).
Apart from that, first-born and only-born children also tend to attribute others’ work
accomplishment to the internal locus of control. This gives them the extra strive for higher
achievement as compared to later-born (Phillips and Phillips, 1994 as cited by Guastello &
Guastello, 2002).
As topic is still in the heat of debate, many more research would be conducted to further
studies on the relationship of birth order and intelligence as the topic has not found its stand.
Therefore, the debate on this topic would promise more new findings in the future.
Statement of Problem
The findings of previous research have found the older sibling to be comparatively
smarter than younger siblings. Based on these findings, families often treat the firstborn as an
academically smart individual, and the younger siblings merely fulfil the other roles: the rowdy
one, the flirt and other niches that are usually unconstructive (Carey, 2007). Due to this problem,
it is hypothesized that many people label others based on their predicted intelligence, especially
parents labeling their children based on their birth order.
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This situation especially limits the growth of the younger siblings as parents would tend
to undermine their abilities and intellectual abilities. The birth order may somehow affect a
person’s intelligence but it should not be the basis of judging one’s intelligence.
Some on the other hand, are not aware of the capabilities and limitations of a particular
child. This situation would be stressful to children who are urged to perform beyond their
capabilities. Therefore, it would not be wise to either judge or overestimate a child’s capabilities.
Target Group
Due to the basis of this study on birth order and intelligence, it would hold great
significance as it would be of a certain interest to nearly everyone in Malaysia. The group of
people that would be particularly interested in this study would be researchers, educators, parents
and the children themselves.
Research Objectives
The main objective of this research is to explore the relationship between birth order and
intelligence in Malaysian children. Is there any significant pattern between the two in the context
of the Malaysian society? Does the birth order affect intelligence in the context of Malaysian
culture?
Significance of Study
The outcome of this study would be helpful to educators as well as parents, to understand
the strong points along with the limitations of a child in performing a certain task. By knowing
these limitations, the child would not be strained to follow the footsteps and match or better the
achievement of the more successful siblings. This study should not be used as a basis of judging
one’s abilities as each person has the potential for growth and improvising themselves. An
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individual should not be contained within a certain label and also submit to the conditions that
comes together with the label.
Research Question
The research is designed to address the research question of “Is there any significant
relationship between birth order and intelligence in Malaysian children?”. This question
illuminates the connection between birth order and intelligence in the context of Malaysian
children.
Hypothesis
A research hypothesis formed would be that there is a significant relationship between
the birth order and intelligence. To specify the hypothesis a little more, an assumption that the
younger sibling would illustrate a higher level of intelligence as compared to the older sibling.
Alternate Hypothesis. There is a significant positive relationship between birth order and
intelligence in Malaysian children.
Null Hypothesis. There is no significant relationship between birth order and
intelligence in Malaysian children.
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CHAPTER II
METHODOLOGY
The data collection design used in this study is the quantitative research method, where
the numerical data or anything that is quantifiable is collected and analyzed to provide suitable
explanations (Hopkins, 2000). The method uses statistical summaries to present the obtained
results.
This study is also a cross-sectional research design, as all the participants will only be
assessed once to have the relationship between the variables determined (Hopkins, 2000). A
cross-sectional study is quick and can be used to examine a large number of sample with little
cost and effort.
Participants
The study population addresses children in all states of Malaysia. As for the sample
population, a part of the population being examined, 65 participants consisting of 20 males and
45 females, aged between 10 and 11 years old, in the area of Klang Valley are chosen. The
samples were selected based on a non probability sampling or convenience sampling (see Table
2.1, pg 12).
Place
The study was conducted in a designated empty classroom at Sekolah Kebangsaan
Taman Desa situated in Taman Desa, Kuala Lumpur. The location was chosen to the
convenience of the participants, school administrator and researcher.
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Table 2.1:
Summary of participants’ sampling
Birth Order Gender Age10 years 11 years
First-born / Only child
Male 2 4Female 8 9
Middle-born Male 5 1Female 7 3
Last-born Male 6 2Female 9 9
TOTAL 65
Measurement Tools
Kaufman Brief Intelligence Scale, 2nd Edition (KBIT2). KBIT2 is administered to assess
the participants IQ in addition to a demographic data. The demographic data includes gender,
age, birth date, race, position in family (birth order), number of siblings and the main language
spoken at home.
The questions are designed to measure a person’s verbal and nonverbal cognitive ability.
The verbal score comprises of two subsets (verbal knowledge and riddles) and it measures
verbal, word knowledge, general information, verbal concept formation and reasoning. As for the
non verbal score (matrices subset), it calculates the ability to solve new problems by recognizing
relationships and the entire visual analogy (Kaufman & Kaufman, 2004).
From a hypothetical standpoint, the verbal division computes crystallized ability where
else the non verbal division assess the fluid reasoning (Kaufman & Kaufman, 2004).
Equipments. Apparatus used in the process includes a pen to answer the questionnaire as
well as to jot down the scores obtained; a calculator to work out to IQ scores of the participants;
and finally a computer to key in and analyze the data gained.
Birth order and intelligence 13
Computer Software. The computer software utilized is the Windows XP Home Edition.
Apart from that, Microsoft Word is used to generate the written report of the research. Also, a
statistical program, Statistical Package for Social Science (SPSS) 12.0 for Windows, is used to
analyze the figures gained from the questionnaires collected.
Procedure
A suitable school in the Klang Valley was chosen. The headmistress of the specific
school was contacted and briefed regarding the research. A letter was prepared under the name of
Universiti Tunku Abdul Rahman (UTAR) to acquire consent. A consent form was signed by the
school’s headmistress after agreeing to the conditions of the research. The teacher in charge then
selected 60 participants from the school’s 10 and 11 year olds that meet the requirements.
The test was administered on two different days (15 and 16 January 2008), by conducting
the test with one age group per day. The participants were placed in a classroom on the specified
date and instructions were given when the participants were seated. 40 to 45 minutes was given
to the participants to complete the intelligence test. All completed questionnaires were then
returned to the researcher. Test scores are calculated and analyzed using the SPSS program.
Reliability and Validity
Intelligence Quotient (IQ). IQ is now recognized as a reliable source to measure and
quantify the intelligence of a person (Baron & Kalsher, 2002). IQ scores are also highly
predictive of real-world outcomes (academic performance, performance on the job, general
adjustment and health) (Hetherington, Parke, Gauvain & Locke, 2006).
Kaufman Brief Intelligence Test, 2nd Edition (KBIT2). According to Kaufman and
Kaufman (2004), the test has high internal-consistency reliability between the subsets ranging
Birth order and intelligence 14
from 0.86 to 0.88. The reliability of the IQ composite is excellent by reporting a reliability
coefficient of 0.93 among children ages 10 to 18.
As for its validity, KBIT2 takes in to account the age variable that leads to the increasing
and decreasing of raw scores. A table portraying the means and standard deviation of raw scores
for each age group is presented. The results across the age range of 4 to 90 presents a strong
foundation for the construct validity (Kaufman & Kaufman, 2004).
Data Analysis
The data gained in the test are compiled and calculated. Statistical analysis was managed
using the SPSS program. Based on the calculated data, the samples are recoded into three birth
order groups, which are first-born and only child, middle-born and last-born. The Pearson
correlation was also administered to examine the relationship between birth order and IQ.
Gender and birth order was also selected in further analysis.
Birth order and intelligence 15
CHAPTER III
RESULTS
Descriptive statistics
From the tabulated data, it is shown that from the 65 samples obtained, 30.8% consists of
males and 69.2% of females. As for the age range, there is 56.9% of 10 year olds and 43.1% 11
year olds. The sample is made up of 44.6% of Chinese, followed by 30.8% Malays, 21.5% of
Indians and 3.1% of other races (Punjabi). The main language spoken at home is divided into
two languages which are Bahasa Melayu (21.5%) and English (78.5%). From the sample, there is
40.0% of last-born, 32.3% of first-born, 24.6% of middle-born and only 3.1% as the only child.
From the total samples of first-born and only child, 10 individuals scored average IQ
composite, 11 scoring above average and only 2 in to the upper extreme. As for middle born, 11
attained average IQ composite scores, where else 3 with above average and 2 in upper extreme.
Finally, 9 last-born scored on the average level, while 14 achieving above average and 3 with
upper extreme IQ composite (see Figure 3.1, pg 15).
Figure 3.1: Distribution of IQ composite and birth order
Birth order and intelligence 16
Further detailed distribution of IQ composite scores (verbal knowledge and non verbal
knowledge) between birth order is shown (see Table 3.1, pg 16).
Table 3.1:
Distribution of IQ range and birth order
Birth Order IQ Range Verbal Knowledge
Non Verbal Knowledge
IQ Composite
First-born and Only child
Below Average - - -
Average 9 13 10
Above Average 9 9 11
Upper Extreme 5 1 2
Middle-born Below Average 2 - -
Average 9 10 11
Above Average 1 6 3
Upper Extreme 4 - 2
Last-born Below Average 2 - -
Average 6 19 9
Above Average 15 6 14
Upper Extreme 3 1 3
TOTAL 65 65 65
Birth order and intelligence 17
Hypothesis: There is a significant relationship between birth order (position in family) and IQ
The result of Pearson’s correlation showed that there is no significant relationship
between the birth order with IQ composite, r (65) = 0.109, n.s. As subsets of the IQ composite,
the verbal knowledge, r (65) = 0.161, n.s., and non verbal knowledge, r (65) = 0.049, n.s., also
revealed non significant results (see Table 3.2, pg 17). Therefore, the null hypothesis is being
accepted.
Table 3.2:
Correlation – Birth order and IQ composite
Birth Order IQ Composite
Verbal Knowledge
Non Verbal Knowledge
Birth Order Pearson Correlation
1 -.105 -.171 -.085
P-Value . .407 .174 .502
IQ Composite
Pearson Correlation
-.105 1 .795** .416**
P-Value .407 . .000 .001
Verbal Knowledge
Pearson Correlation
-.171 .795** 1 .224
P-Value .174 .000 . .072
Non Verbal Knowledge
Pearson Correlation
-.085 .416** .224 1
P-Value .502 .001 .072 .
**. Correlation is significant at the 0.01 level (2-tailed)
Birth order and intelligence 18
Since there is no significant relationship between birth order and IQ, further examination
shows that the result of the Pearson’s correlation showed that there is a positive significant
correlation between the verbal knowledge and IQ composite in the first-born and only child, r
(23) = 0.777, p<0.01 (see Table 3.3, pg 18). This illustrates that first-born are better in verbal
knowledge.
Table 3.3:
Correlation – Relationship between first born and only child with IQ
IQ Composite Verbal Knowledge
Non Verbal Knowledge
IQ Composite Pearson Correlation
1 .777** .335
P-Value . .000 .119Verbal
KnowledgePearson
Correlation.777** 1 .090
P-Value .000 . .683Non Verbal Knowledge
Pearson Correlation
.335 .090 1
P-Value .119 .683 .**. Correlation is significant at the 0.01 level (2-tailed).
Birth order and intelligence 19
It is shown from the result of the Pearson’s correlation that there is also a positive
significant correlation between the verbal knowledge and IQ composite in middle-born, r (16) =
0.884, p<0.01 (see Table 3.4, pg 19). Thus, middle born is also good in verbal knowledge.
Table 3.4:
Correlation - Relationship between middle-born with IQ
IQ Composite Verbal Knowledge
Non Verbal Knowledge
IQ Composite Pearson Correlation
1 .884** .252
P-Value . .000 .346Verbal
KnowledgePearson
Correlation.884** 1 -.081
P-Value .000 . .766Non Verbal Knowledge
Pearson Correlation
.252 -.081 1
P-Value .346 .766 .**. Correlation is significant at the 0.01 level (2-tailed).
Birth order and intelligence 20
As for the last-born, the result of the Pearson’s correlation shows that there is a positive
significant relationship between both verbal knowledge, r (26) = 0.741, p<0.01 and non verbal
knowledge, r (26) = 0.654, p<0.01, with IQ composite (see Table 3.5, pg 20). It is deduced that
last-born is good in both verbal and non verbal knowledge.
Table 3.5:
Correlation - Relationship between last-born with IQ
IQ Composite Verbal Knowledge
Non Verbal Knowledge
IQ Composite Pearson Correlation
1 .741** .654**
P-Value . .000 .000Verbal
KnowledgePearson
Correlation.741** 1 .576**
P-Value .000 . .002Non Verbal Knowledge
Pearson Correlation
.654** .576** 1
P-Value .000 .002 .**. Correlation is significant at the 0.01 level (2-tailed).
Birth order and intelligence 21
After seeing that there are differences in the relationship between birth order and the
subsets of IQ, the research is further refined to include gender as a variable.
Firstly, for first-born and only child, the result of the Pearson’s correlation shows that
there is no significant relationship between verbal knowledge and IQ composite, r (6) = 0.707,
n.s., and also non verbal and IQ composite, r (6) = 0.316, n.s., in males (see Table 3.6, pg 21).
There is no credible connection between birth order and IQ as the sample consists of only 6
participants.
Table 3.6:
Correlation - Relationship between first-born and only child males with IQ
IQ Composite Verbal Knowledge
Non Verbal Knowledge
IQ Composite Pearson Correlation
1 .707 .316
P-Value . .116 .541Verbal
KnowledgePearson
Correlation.707 1 -.447
P-Value .116 . .374Non Verbal Knowledge
Pearson Correlation
.316 -.447 1
P-Value .541 .374 .**. Correlation is significant at the 0.01 level (2-tailed).
Birth order and intelligence 22
On the other hand, the result of the Pearson’s correlation shows that there is a significant
correlation between verbal knowledge and IQ composite in female first-born and only child, r
(17) = 0.823, p<0.01 (see Table 3.7, pg 22). This implies that female first-born and only child
are decent in the acquirement of verbal knowledge.
Table 3.7:
Correlation - Relationship between first-born and only child females with IQ
IQ Composite Verbal Knowledge
Non Verbal Knowledge
IQ Composite Pearson Correlation
1 .823** .364
P-Value . .000 .151Verbal
KnowledgePearson
Correlation.823** 1 .072
P-Value .000 . .784Non Verbal Knowledge
Pearson Correlation
..364 .072 1
P-Value .151 .784 .**. Correlation is significant at the 0.01 level (2-tailed).
Birth order and intelligence 23
The result of the Pearson’s correlation shows that there is a significant correlation
between both verbal knowledge and non verbal knowledge with IQ composite in middle-born
males, r (6) = 1.000, p<0.01 (see Table 3.8, pg 23). Middle-born males are shown to be
respectable in getting hold of both the verbal and non verbal knowledge.
Table 3.8:
Correlation - Relationship between middle-born males with IQ
IQ Composite Verbal Knowledge
Non Verbal Knowledge
IQ Composite Pearson Correlation
1 1.000** 1.000**
P-Value . . .Verbal
KnowledgePearson
Correlation1.000** 1 1.000**
P-Value . . .Non Verbal Knowledge
Pearson Correlation
1.000** 1.000** 1
P-Value . . .**. Correlation is significant at the 0.01 level (2-tailed).
Birth order and intelligence 24
Moving on, the result of the Pearson’s correlation shows that there is a significant
positive relationship between verbal knowledge and IQ composite, r (10) = 0.890, p<0.01, but no
significant correlation is shown between non verbal knowledge and IQ composite in middle-born
females, r (10) = 0.111, n.s. (see Table 3.9, pg 24). This means that middle-born females are
excellent in the attainment of verbal knowledge but lack the sparkle in terms of non verbal
knowledge.
Table 3.9:
Correlation - Relationship between middle-born females with IQ
IQ Composite Verbal Knowledge
Non Verbal Knowledge
IQ Composite Pearson Correlation
1 .890** -.535
P-Value . .001 .111Verbal
KnowledgePearson
Correlation.890** 1 -.650*
P-Value .001 . .042Non Verbal Knowledge
Pearson Correlation
-.535 -.650* 1
P-Value .111 .042 .*. Correlation is significant at the 0.05 level (2-tailed).
**. Correlation is significant at the 0.01 level (2-tailed).
Birth order and intelligence 25
In deeper analysis of last-born, the result of the Pearson’s correlation shows that there is a
significant positive relationship between verbal knowledge and IQ composite, r (8) = 0.908,
p<0.01, and non verbal with IQ composite, r (8) = 0.777, p<0.05, in males (see Table 3.10, pg
25). The last-born males are revealed to have better comprehension of both verbal and non verbal
knowledge.
Table 3.10:
Correlation - Relationship between last-born males with IQ
IQ Composite Verbal Knowledge
Non Verbal Knowledge
IQ Composite Pearson Correlation
1 .908** .777*
P-Value . .002 .023Verbal
KnowledgePearson
Correlation.908** 1 .747*
P-Value .002 . .033Non Verbal Knowledge
Pearson Correlation
.777* .747* 1
P-Value .023 .033 .*. Correlation is significant at the 0.05 level (2-tailed).
**. Correlation is significant at the 0.01 level (2-tailed).
Birth order and intelligence 26
In last-born females, the result of the Pearson’s correlation also shows that there is a
significant relationship between both verbal knowledge with IQ composite, r (18) = 0.616,
p<0.01, and non verbal with IQ composite, r (8) = 0.531, p<0.05 (see Table 3.11, pg 26). Last-
born females are also equally as proficient as last-born males in the acquisition of verbal and non
verbal knowledge.
Table 3.11:
Correlation - Relationship between last-born females with IQ
IQ Composite Verbal Knowledge
Non Verbal Knowledge
IQ Composite Pearson Correlation
1 616** .531*
P-Value . .007 .023Verbal
KnowledgePearson
Correlation.616** 1 .417
P-Value .007 . .085Non Verbal Knowledge
Pearson Correlation
.531* .417* 1
P-Value .023 .085 .*. Correlation is significant at the 0.05 level (2-tailed).
**. Correlation is significant at the 0.01 level (2-tailed).
Birth order and intelligence 27
CHAPTER IV
DISCUSSION
Birth Order and Intelligence
Referring back to the results of the study, it was found that there is no significant
relationship between birth order and intelligence in Malaysian children. Thus, it can be
concluded that a child’s intelligence is not affected by his or her position in a family (birth
order). The result of the study supports the idea of Rodgers et. al. (2000) that the linkage between
birth order and intelligence is purely a mechanical delusion.
The available research that supports the findings is done in direct comparison between IQ
scores of siblings in the same family. In a relatively recent research, Wichman (2006) has
concluded that there is no relationship between birth order and intelligence. Rodgers and
colleagues (2000) attributed that there is no birth order effect on IQ as direct comparison of
siblings within the same family removes the possibility of any confounding variables such as
family size (Harris, 2001). This research also dates back to 1973, where there was a reported
negative association between birth order and intelligence in young Dutch men (Kristensen &
Bjerkedal, 2007).
From the many research done, several conclude that there is a connection between the
two variables. Then again, based on an argument by Wichman, Rodgers and MacCallum (2007),
these differences are due to the fact that data is collected based on the cross-sectional design and
also samples taken from between families and not intra-familial (Sayfer, 2007). Comparatively,
the results obtained from the study of Malaysian children shows that IQ nonetheless does not
affect birth order in children despite the samples being from different families and also the use of
cross sectional research design.
Birth order and intelligence 28
Results of the study also showed that there is a significant relationship between verbal
knowledge and IQ composite in first-born, only-born and middle-born children. But in the case
of the last-born, there is a significant relationship between both verbal knowledge and non verbal
knowledge with IQ composite. In other words, there is a connection between the position in the
family and the ability of acquiring of knowledge. First-born, only-born and middle-born children
are seen to be related to the acquisition of verbal knowledge where else last-born children are
associated to both. How do we explain this scenario?
By being the first-born or only child, they are given the fullest of attention and discipline
by their parents (Clayton, 1998). Parents also tend to be more restrictive, overly anxious and
have high expectations towards the child, thus exposing them to more adult thinking (Walton,
2001). With the strict supervision of parents, it guides the first-born and only-born to go hand-in-
hand with the reflected dreams of each parent (Child Development Institute, 2007). The
undivided attention given as infants provides the first-born and only-born children with
additional cumulative adult attention, which leads to enrichment of vocabulary and reasoning
(Carey, 2007). Owing to this situation, first-born and only-born children tend to be high
achievers, in a sense, good with verbal knowledge (Hetherington, Parke, Gauvain, Locke, 2006).
The fact that first-born children have to fulfill the role as a tutor to younger siblings has
also benefited the child (Carey, 2007). When a younger sibling proposes a question, it triggers
the tutor to think intensively making them gain an intellectual advantage (Evans & McClintic,
2002).
Another reasoning to why first-born and only-born are better in verbal knowledge is that
they have high “need for achievement” (nAch) (Falbo & Polit, 1986 as cited by Wood, Wood &
Boyd, 2004). As nAch mostly focuses on gaining accomplishments, for a child, the best triumph
Birth order and intelligence 29
would be in the academic achievements. In Malaysia, the academic system is focused more on
the verbal, word knowledge, concept formation and reasoning rather than creative thinking.
Consequently, first-born and only-born tend to be high achievers in schools.
It would be more difficult to explain the relationship between verbal knowledge and IQ
composite in middle born as not many research has been done on this group. Middle-born
children are required to share parental resources with either the older or younger sibling
(Hertwig, Davis, & Sulloway, 2001 as cited by Sulloway, n.s.). With this, they are more
independent in all aspects in order to be able to compete with the other siblings (especially the
older sibling) for parental attention (Sulloway, n.s.). In order to compete with the older sibling,
the middle-born needs to improve and be independent in acquiring knowledge, mostly verbal
knowledge (Rimm, 2002).
From reasoning, although tutoring is not dominant in middle-born children, they too
share the opportunity to guide and mentor the younger siblings, which in turns provides the
similar effects for the middle-born children (Carey, 2007).
Why does the IQ composite of last-born children have a relationship with both verbal and
non verbal knowledge? Normally, the youngest child would be favored more by the parents,
which would very much develop the child’s intelligence. This is due to the increasing contact
hours spent with the parents (Steckel, 1930 as cited by Walton, 2001). It is shown that the
average intelligence of later-born children was superior to those of earlier-born children (Walton,
2001). Even if last-born children have better verbal knowledge, how does non verbal knowledge
come in to place?
Parents control over their children decrease with birth order. They may be entirely strict
with the first-born but for the last-born, they can be extremely lenient (Walton, 2001). Last-born
Birth order and intelligence 30
children are also given less responsibilities which enable them to spend more time exploring the
surroundings. Due to the extrovert nature of last-born children, they are more exploratory and
creative (Sulloway, n.s.), and this presents the last-born children the upper hand in non verbal
knowledge (resolving new problems and identifying relationships).
For first-born, only-child and middle-born children, the main source of social learning is
entirely focused on the parent itself where else the last-born children are able to refer to both
parents and older siblings as models and teachers (Dunn, 1993 as cited in Hetherington, Parke,
Gauvain, Locke, 2006). This gives them the advantage to gain more information as compared to
the other birth order groups.
As for the detailed analysis of gender and the components of intelligence, there is no
significant relationship between gender and intelligence. Findings from male and female
respondents have only a slight variation. This is supported by a research stating that sex has
diminutive or no effect on IQ scores (Carey, 2007).
Also according to the Oxford University Press (2000), men and women have similar
average scores on various tests of intelligence. Kaufman and Kaufman (2004) also take in to
account the gender variable in devising an intelligence test, whereby affirming that there is very
minute sex differences in intelligence.
Limitations and Recommendations of Study
The study is conducted to look at the relationship between birth order and intelligence of
children in Malaysia. There are several limitations that are unavoidable. One of it would be the
sample size. The participants were only selected from a particular school in the Klang Valley and
also a specified age. It would be hard to generalize the sample to the whole of Klang Valley,
what more Malaysia. Therefore, if the issue is to be further researched on, a larger sample size
Birth order and intelligence 31
that includes obtaining a more distributed sample throughout the states in Malaysia would help in
terms of the reliability and accuracy of findings.
Apart from that, the applicability of KBIT2 also showed some cultural influence. A small
part of the questions in KBIT2 is beyond the knowledge range of Asians, as well as the inclusion
of culture sensitive pictures. The pictures were either removed or replaced based on the context
of the question. For further research purposes, a more suitable test should be founded or
modification of the original test based on the needs of the samples.
Finally, a suggestion for additional research is to look in to the research method and intra-
familial samples. This is to distinguish whether these two factors do influence the outcome of the
study.
Conclusion
As a conclusion, there is no significant relationship between birth order and intelligence
in the context of Malaysian children. Despite these results, the last-born child is shown to have a
wider field of knowledge (verbal and non verbal knowledge) compared to the other birth order
categories. On the other hand, this does not entirely degrade the other children in the family as
they too have the advantage in the acquisition of verbal knowledge (reasoning and general
knowledge).
Birth order and intelligence 32
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