Psychological Research Methods


case study

research examining a single person or group in detail over a period of time

confounding variable

uncontrolled factor that a researcher did not account for in a study, but that could influence study outcomes

control group

group containing participants who do not receive treatment or participate in the experimental condition

convenience sampling

when researchers recruit participants from the easiest-to-access members of a population

correlation coefficient

numerical value between –1 and +1 that represents the strength and direction of a relationship between variables

correlational research

research examining the strength and direction of a relationship between variables

demand characteristics

cues leading participants to behave in a way they think is desirable during a study rather than behaving naturally

dependent variable

the variable being measured by a researcher

descriptive statistics

statistics that summarize a data set

double-blind procedure

procedure in which neither the experimenter nor the participant knows the group to which a participant belongs

effect size

a measure of the magnitude of a finding

experimental group

group containing participants who receive treatment or participate in an experimental condition

experimental research

research design allowing researchers to draw conclusions about cause and effect

experimenter bias

when a researcher who knows the intended outcome of the study influences the procedure or outcome in some way

independent variable

variable being changed or manipulated by a researcher

inferential statistics

statistics that generalize conclusions from a sample to a larger population

informed consent

agreement to participate in research based on a complete understanding of the procedure, risks, and benefits of a study


measure of central tendency calculated by adding all values in a data set and dividing the sum by the total number of values


value in a data set where half the values fall below it and half are above it


most frequently occurring value in a data set

normal distribution

a symmetrical, bell-shaped distribution in which most values fall near the mean

operational definition

specific description of how a variable will be measured as determined by the researcher

placebo effect

when participants think they are in the experimental group and their thoughts, feelings, or behavior changes as a result of this expectation

random assignment

process in which each participant has an equal chance of being placed in either the experimental or control group


numerical difference between the highest and the lowest value in a data set


extent to which assessment scores remain consistent across time, settings, or raters

representative sample

group of participants whose characteristics match those of the larger target population

standard deviation

measure of how much values differ from the mean

statistical significance

statement of the probability that an observed result occurred due to chance


extent to which an assessment tool accurately measures the variable of interest