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Research Methods of Psychologists
Critical Thinking thinking that does not blindly accept arguments and conclusions
examines assumptions; discerns hidden values; evaluates evidence
Limits to critical thinking
Hindsight Bias -- tendency to believe, after learning an outcome, that one would have foreseen it (the “Iknew-it-all-along” phenomenon)
Overconfidence -- we tend to think we know more than we do
Research Strategies
Theory -- an explanation using an integrated set of principles that organizes and predicts observations
Hypothesis -- a testable prediction (often implied by a theory)
Replication -- repeating the essence of a research study to see whether the basic finding generalizes to
other subjects and circumstances; usually with different subjects in different situations
False Consensus Effect -- tendency to overestimate the extent to which others share our beliefs and
behaviors
Confirmation bias – Researchers look for results that confirm their hypothesis
Types of Research Studies
Case Study -- an observation technique in which one person is studied in depth in the hope of revealing
universal principles
Survey -- technique for ascertaining the self-reported attitudes or behaviors of people, usually by
questioning a representative, random sample of them
Naturalistic Observation -- observing and recording behavior in naturally occurring situations without
trying to manipulate and control the situation
Correlation -- a statistical measure that indicates the extent to which two factors vary together and thus
how well either factor predicts the other
Problem: Illusory Correlation -- the perception of a relationship where none exists
Experiment -- a research method in which the investigator manipulates one or more factors (independent
variables) to observe their effect on some behavior or mental process (the dependent variable)
while controlling other relevant factors by random assignment of subjects
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
Random Selection – a method of choosing participants for the study from the population. Can
pick out of a hat, or generate a list of random numbers and have a computer choose the subjects.
Random Assignment -- assigning subjects to experimental and control conditions by chance
(minimizes pre-existing differences between those assigned to the different groups)
Independent Variable -- the experimental factor that is manipulated (the variable whose effect is
being studied)
Dependent Variable -- the experimental factor that may change in response to manipulations of
the independent variable (in psychology it is usually a behavior or mental process)
Confounding Variable – any variable that is not controlled that can interfere with the reliability of
the study
Operational Definition -- a statement of the procedures (operations) -- used to define research
variables
Placebo – a 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
Double-blind procedure -- an experimental procedure in which both the subject and the research
staff are ignorant (blind) about whether the subject has received the treatment or a placebo
**commonly used in drug-evaluation studies
Descriptive Statistics
Measures of central tendency
Mean – average score
Mode – most frequent score
Median – middle score
Measures of relationships
Correlation coefficient – ranges from -1.00 to 1.00
Positive correlation – both measures go in same direction (ex. As height increases, weight increases)
Negative correlation – measures go in opposite direction (ex. As caffeine levels rise, calmness falls)
Plotting data
Normal curve – Bell-shaped curve - typical distribution of any set of scores
Skewed distribution – unusual distribution of scores with a spike of scores on one end of the
distribution (skewed right – spike is at left, skewed left – spike is at right)
Measures of variability
Range – difference between high and low scores in the distribution
Standard deviation – based on normal curve, measure of the average distance of each score from
the mean score. If S.D. is small, scores will be close together (the average distance from the mean
is very small). 68% of the scores fall between one standard deviation on each side of the mean;
95% fall within two standard deviations on each side of the mean; 99.7% fall within three standard
deviations on each side of the mean.
Variance = standard deviation squared
Inferential statistics
Statistical significance – chance that results would occur randomly – commonly must meet 5%
threshold (Alpha level or p<.05)
Sampling
Random sample – must choose participants in a study at random from a given population
Stratified sample – must choose from representative groups of the population (e.g. study on correlating
hair color to intelligence)