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experiment

A research method in which a researcher manipulates one variable to determine whether it causes changes in another variable.

independent variable

The variable that is manipulated or changed by the researcher in an experiment.

dependent variable

The variable that is measured in an experiment and changes in response to the independent variable.

control variable

Any variable that is kept constant in an experiment to prevent interference with the results.

population

The entire group of people or subjects that a researcher wants to study.

representative sample

A sample that accurately reflects the characteristics of the population being studied.

representativeness

The degree to which a sample accurately mirrors the population.

experimental group

The group in an experiment that receives the treatment or independent variable.

control group

The group in an experiment that does not receive the treatment and is used for comparison.

random sampling

A process in which every member of a population has an equal chance of being selected for a study.

randomly assigned

The process of placing participants into groups by chance to reduce bias.

biases

Systematic errors or influences that distort results and reduce the accuracy of research.

bias of selection

A type of bias that occurs when participants are chosen in a way that makes the sample unrepresentative.

self-selection bias

Bias that occurs when people choose whether or not to participate, creating unrepresentative groups.

pre-screening advertising bias

Bias created when the wording or advertisement for a study attracts specific participants.

healthy user bias

A bias where healthier individuals are more likely to participate in research, skewing results.

single-/double-blind design

A design where participants (single-blind) or both participants and researchers (double-blind) do not know group assignments.

placebo

An inactive substance or fake treatment given to the control group to measure psychological effects.

correlational research

A research method that examines relationships between variables without manipulating them.

confounding/third/extraneous variable

A variable other than the independent variable that may affect the dependent variable.

surveys

Research methods that collect self-reported information from participants via questionnaires or interviews.

longitudinal studies

Studies that follow the same participants over a long period to observe changes.

cross-sectional studies

Studies that compare different groups of people at one point in time.

clinical research

Research focused on diagnosing, understanding, or treating psychological disorders.

case studies

An in-depth investigation of one person or a small group to gather detailed information.

generalizable

Able to apply research findings from a sample to the larger population.

conceptual definition

A general explanation of a concept or variable in theory.

operational definition

A precise explanation of how a variable is measured or manipulated in a study.

internal validity

The degree to which an experiment accurately shows cause-and-effect relationships without interference.

external validity

The degree to which research findings can be generalized to other settings or populations.

reliability

The consistency or repeatability of research results.

inter-rater reliability

The degree to which different observers agree in their measurements.

naturalistic observation

A research method in which behavior is observed in a natural environment without interference.

qualitative research

Research that focuses on descriptive, non-numerical data such as interviews and observations.

descriptive statistics

Statistical methods used to organize, summarize, and describe data.

inferential statistics

Statistical methods used to draw conclusions about a population based on sample data.

central tendency

A measure that identifies the center or average of a distribution.

mean

The arithmetic average of a set of numbers.

mode

The most frequently occurring score in a distribution.

bimodal

A distribution with two modes or most frequently occurring scores.

median

The middle score in a distribution when arranged from lowest to highest.

normal curve

A symmetrical, bell-shaped distribution with scores clustering around the mean.

range

The difference between the highest and lowest scores in a distribution.

variability

The extent to which scores differ from one another in a distribution.

standard deviation

A measure of how spread out scores are in a distribution.

percentile

A score indicating the percentage of scores below a given score.

positive skew

A distribution where the tail extends to the right due to high scores.

negative skew

A distribution where the tail extends to the left due to low scores.

correlation coefficient

A numerical measure from -1.00 to +1.00 indicating the strength and direction of a relationship.

Pearson correlation coefficient

The most common correlation coefficient used to measure linear relationships.

positive correlation

A relationship in which two variables increase or decrease together.

negative correlation

A relationship in which one variable increases while the other decreases.

sample size

The number of participants or observations included in a study.

null hypothesis

A prediction stating there will be no effect or relationship between variables.

alternative hypothesis

A prediction stating there will be an effect or relationship between variables.

alpha

The significance level used in hypothesis testing, often set at 0.05.

Type I error

A false positive, rejecting the null hypothesis when it is actually true.

Type II error

A false negative, failing to reject the null hypothesis when it is actually false.

p-value

The probability that results occurred by chance.

deception

Misleading participants about the true purpose of a study when necessary for research validity.

Stanley Milgram

A psychologist known for his obedience experiments studying authority obedience.

confederates

People secretly working with researchers while pretending to be participants.

Institutional Review Boards (IRBs)

Committees that review research studies to ensure ethical treatment of participants.

informed consent

The process of giving participants enough information about a study to decide about participation.

debriefing

Explaining the true purpose of a study to participants after it ends.

confidentiality

Protecting participants’ private information and keeping research data secure.