Research Methods in Psychology

StrategiesStatistics& Ethics

Research Strategies

Research Strategies

• Experiment– Researcher changes one or more factors to observe

their effect on some behavior or mental process ⁺ DOES IDENTIFY CAUSE/EFFECT RELATIONSHIP⁻ Sampling errors, placebo effect, not natural environment

could alter true effect

Research Strategies• Case Study (descriptive)

– in depth fact finding on a single subject⁺ Intensive, specific info⁻ No cause/effect; lots of time; no generalization

• Naturalistic Observation (descriptive)– Observation in natural/real setting without changing

environment⁺ Gathers naturally occurring data; real world⁻ Observer bias; no cause/effect

Research Strategies

• Survey Research (descriptive)– Collect data through interviews questionnaires

• {but beware of:}– false consensus effect– bad sampling (especially self-selection!!!)

• Reduces validity and reliability = wording effects

Research Strategies

• Correlational studies (descriptive)– Examines the degree* of relationship between

two variables⁺ Study real world connections⁻ NO cause/effect just CONNECTION– *”degree of relationship” just means how much they

correlate.

Research Strategies

• One last note about correlational studies:

If you HAVE to get a tattoo, then I suggest the following:

“Correlation is not causation.”

Research Strategies

• If marbles of two colors are mixed well in the large jar, the fastest way to know their ratio is to blindly transfer a few into a smaller one and count them

Research Strategies

• Population– all the cases in a group, from which samples

may be drawn for a study

• Random Sample– a sample that fairly represents a population

because each member has an equal chance of inclusion

• Stratified random samples

Experiments (cont…)

• Three Possible Cause-Effect Relationships(1)

Low self-esteemDepression

(2)Depression

Low self-esteem

Low self-esteem

Depression

(3)Distressing events

or biologicalpredisposition

could cause

could cause

could cause

or

or

and

Controls

• Single & Double-blind Procedures– Subjects (or both the subjects and the research

staff )are ignorant (blind) about whether the subject has received the treatment or a placebo

– commonly used in drug-evaluation studies• Placebo

– an inert substance or condition that may be administered instead of a presumed active agent, such as a drug, to see if it triggers the effects believed to characterize the active agent

Controls

• Random Assignment–assigning subjects to experimental and

control conditions by chance–minimizes pre-existing differences

between those assigned to the different groups

Controls

• Experimental Condition– the condition of an experiment that exposes

subjects to the treatment, that is, to one version of the independent variable

• Control Condition– the condition of an experiment that contrasts with

the experimental treatment – serves as a comparison for evaluating the effect of

the treatment

Controls

• Independent Variable – the hypothesized cause of a phenomenon– typically manipulated by experimenter

• Dependent Variable – the hypothesized effect in a phenomenon– in psychology it is usually a behavior or mental

process – measured by the experimenter

Controls

• So how do you control for the big daddy of confounds, Chance?– Random assignment to conditions PLUS– Inferential statistics

Research Strategies

Comparing Research MethodsResearch Method Basic Purpose How Conducted What is

Manipulated

Descriptive - To observe and Case studies, surveys, NothingOne variable at record behavior and naturalistica time observations

Descriptive - To detect naturally Computing correlations NothingTwo variables occuring relationship , sometimesat a time to assess how well among survey

one variable predicts responses

Experimental To explore cause Manipulating one or Independent and effect more factors and using variable(s)

random assignmentto eliminate preexistingdifferences among subjects

Statistics

• Statistics come in two basic flavors:– Descriptive (duh.)– Inferential : did my observed result REALLY happen,

or was it just by chance?

Descriptive stats tell you 3 basic things:1.Central tendency2.Variability3.Correlation

• Mode– the most frequently occurring score in a distribution

• Mean– the arithmetic average of a distribution– obtained by adding the scores and then dividing by the

number of scores• Median

– the middle score in a distribution– half the scores are above it and half are below it

Mathematical Tools-- Central Tendency --

• Range– the difference between the highest and lowest scores

in a distribution• Standard Deviation

– a computed measure of how much scores vary around the mean

• Statistical Significance– a statistical statement of how likely it is that an

obtained result occurred by chance

Mathematical Tools-- Variation --

Mathematical Tools-- Covariation --

• Correlation Coefficient– a statistical measure of the extent to which two factors vary together and

thus how well either factor predicts the other

Correlation coefficient

Indicates directionof relationship

(positive or negative)

Indicates strengthof relationship(0.00 to 1.00)

r = +.37

Mathematical Tools

Height and Temperament of 20 Men

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10

11121314151617181920

80636179746962757760

64767166737063716870

75666090604242608139

48697257637530578439

SubjectHeight in

Inches Temperament SubjectHeight in

Inches Temperament

Mathematical Toolsaka Statistical Reasoning

• Scatterplot– a graphed cluster of dots, each of which represents

the values of two variables– the slope of the points suggests the direction of the

relationship– the amount of scatter suggests the strength of the

correlation• little scatter indicates high correlation

– also called a scattergram or scatter diagram

Mathematical Tools

• Scatterplot of Height and Temperament

55 60 65 70 75 80 85

959085807570656055504540353025

Temperamentscores

Height in inches

Mathematical Tools

Perfect positivecorrelation (+1.00)

No relationship (0.00) Perfect negativecorrelation (-1.00)

Mathematical Tools:Inferential statistics

• SOLE purpose: is this result due to chance or not?– Typically assessed with a “probability value” or “p-

value”– Cut off is usually .05 (but there’s nothing magical

about that number!)– P-values are NOT measures of “effect size”– Effect size is always more important.

Statistical traps…

• Mistaking correlation for causation– the perception of a relationship where none exists– (re: availability)

Statistical traps…Random Sequences

• Your chances of being dealt either of these hands is precisely the same: 1 in 2,598,960.

Statistical traps…Cheating with graphs:

Our Brand Brand BrandBrand X Y Z

100%

99

98

97

96

95

Percentagestill functioningafter 10 years

Brand of truck

Statistical traps…Cheating with graphs

Our Brand Brand Brand Brand X Y Z

100%

90

80

70

60

50

40

30

20

10

0

Percentagestill functioningafter 10 years

Brand of truck

Statistical traps…Which mean is which?

• A Skewed Distribution

15 20 25 30 35 40 45 50 90 475 710

70

Mode Median Mean

One Family Income per family in thousands of dollars

World’s fastest ethics lecture

• Doing research with humans – basic principles:– Rights & well-being of participants outweigh the

benefits of the research

– Participants have to be allowed to decide to participate or not: Informed Consent is the cornerstone of ethical research.

World’s fastest ethics lecture

– Participants have the right to withdraw from the study at any time, without penalty.

– Participants must be protected from risks or informed of risks that can’t be removed. Risk/benefit ratio must be positive.

– Deception is avoided whenever possible and must be justified if it is used.

World’s fastest ethics lecture

– Researchers have the duty to inform the participants of the true purpose of the study (usually done in the debriefing)

– Data must remain confidential and secure (trickier these days with computers!)