Psychological Research Methods

• Learning Target: Compare and contrast research methods (case studies, survey, naturalistic observation, correlational studies)

• Modern psychology aims to be an empirical science, which means that assumptions are supported by scientific evidence

• Psychologists use scientific method to test hypotheses & develop theories

Operational Definition

• Specifies how a variable will be defined and measured

• If my variable is memory, how will I define and measure it?

• Operational Definition: A person has a good memory if they can memorize a list of 30 random words in two minutes or less and then write them down on a sheet of paper.

• Population: the group that is targeted for the study

• Sample: segment of the population to be studied

• Random sample: each member of a population has an equal chance of being selected to participate

• Stratified sample: identified subgroups in the population are represented proportionately in the sample

• Psychologists then draw conclusions based on their observations and findings

• When observations do not support the hypothesis, a psychologist may modify the theory from which the question originated

• Replicate: repeat a study to ensure that data is accurate (if get different results, study is invalid)

• Generalize: apply results to population as a whole

Bias in Research• Volunteer bias: people who offer or

volunteer to participate in research studies differ from those who do not, therefore this skews the findings

• Social desirability bias: many people tend to tell the interviewer what they think the interviewer wants to hear and not what they really think

Validity & Reliability• Validity: when a study measures what the

researchers set out to measure• Reliability: when results of a study be

replicated, are consistent when repeated

Observational Methods: Case Study• Case study: examine one individual or

small group• Pros:

- Detailed & specific info- Good in rare cases

• Cons: - No generalization (unique case)- Cannot test theories

Observational Methods: Survey

• Survey: a large sample of people answer questions about their attitudes or behavior

• Pros: - More info, less time, less $- Better to generalize

• Cons: - Social Desirability Bias- Poor wording - Interviews are less honest or candid – Bathroom study (95% v. 67%)- Inaccurate recall

Observational Methods: Naturalistic Observation

• Naturalistic Observation: subjects are observed in natural environment- No attempt to influence or control

• Pros: - behavior is natural & spontaneous

• Cons: - Wait for behaviors to occur- Observer bias

Jane Goodall

Correlational Method

• Sir Francis Galton (1822-1911)

• Correlation = degree of relationship between variables (r)

• “Correlation does not prove causation”

Example: Data Is income related to years of school?

Income at Age 25 ($)

• 20,500 .75• 33,000 3.25• 30,000 2.5• 23,500 1.25• 32,000 3.5• 27,500 3• 24,000 2.15• 26,000 1.95

Years of College

Fig. 1.9 The relationship between years of college completed and personal income (hypothetical data).

Positive Correlation• As one variable increases, the other variable also

increases (& vice versa)• Values between +0.01 and +1.00

• Among college students, those with higher SAT scores also have higher grades.

• As people’s happiness level increases, so does their helpfulness.

Negative Correlation• As one variable decreases, the other variable increases

(or vice versa)• Values between -1.00 and -0.01

• People who have more years of education tend to have fewer years in jail.

• Among babies, those who are held more tend to cry less.

No Correlation • Value of 0 – neither positive or negative• No linear relationship• For example, hours of sleep and number of stars

in the sky

• http://www.gifted.uconn.edu/Siegle/research/Correlation/scatter/scatterplotdemo.html

Fig. 1.7 The correlation coefficient tells how strongly two measures are related. These graphs show a range of relationships between two measures, A and B. If a correlation is negative, increases in one measure are associated with decreases in the other. (As B gets larger, A gets smaller.) In a positive correlation, increases in one measure are associated with increases in the other. (As B gets larger, A gets larger.) The center-left graph (“medium negative relationship”) might result from comparing anxiety level (B) with test scores (A): Higher anxiety is associated with lower scores. The center graph (“no relationship”) would result from plotting a person’s shoe size (B) and his or her IQ (A). The center-right graph (“medium positive relationship”) could be a plot of grades in high school (B) and grades in college (A) for a group of students: Higher grades in high school are associated with higher grades in college.

Correlations

• Pros:– Can make predictions (but no cause/effect)

• Cons:– No causation

• Importance of sample size!• Possibility of 3rd variable• Illusory correlations (“it always rains

after you wash your car”)

Correlation Does NOT Prove Causation

• “People who floss their teeth more often live longer.”Could there be another reason why people who regularly floss their teeth live longer?People who take care of their teeth probably take care of themselves in other ways too (exercise, proper diet, don’t smoke, etc.)

• “The number of drownings in the U.S. rises and falls during the year, along with the amount of ice cream sold each month.”Third variable (time of year) – summer – more likely to eat ice cream, swim in pools/lakes

Illusory Correlations: Homer Simpson• Springfield invests millions of dollars in a

“Bear Patrol” after a single bear was spotted

• Homer tells Lisa how well the patrol is working – “not a bear in sight”

• Lisa challenges Homer’s conclusion:– Lisa: “By your logic, I could claim this rock

keeps tigers away”– Homer: “How does it work?”– Lisa: “I don’t see any tigers around, do you?”– Homer: “Lisa, I want to buy your rock”

Experimental Method• Researcher manipulates one/more variable(s) to

observe the effect on another variable• Control all conditions except for one or more

variables• Independent Variable: variable manipulated by

experimenter• Dependent Variable: variable which changes due

to I.V. (the effect)

Experimental Method• Experimental group: group of participants which

receives treatment or IV• Control group: group which

not receive treatment while all other variables are held constant

• Randomly assign participants to experimental or control group

• Placebo: fake treatment (i.e. sugar pill)

• Experiments are the only research method that can prove cause & effect

Fig. 1.11 Elements of a simple psychological experiment to assess the effects of music during study on test scores.

Example

• College students’ memory for German vocabulary words is tested after a normal night’s sleep or a night of no sleep

• “If students get more sleep, then they will remember more German vocab”

• IV = sleep• DV = memory of vocab• Control group = normal night’s sleep• Experimental group = no sleep

Experimental Method

• Blind study: subjects are unaware if assigned to experimental or control group

• Double-blind study: neither subjects nor experimenters know which group is control or experimental

Longitudinal v. Cross-sectional Studies

• Longitudinal – same participants over long period of timei.e. studying effects of early childhood literacy program on later academic success

• Cross-sectional – studies participants at one time i.e. effect of a vitamin on memory recall