AP Psych Research Unit 2026

empiricism

the philosophical belief that all human knowledge, thoughts, and behaviors originate primarily from sensory experiences and the environment; relies on observation and experimentation

functionalism

A school of psychology that focused on how our mental and behavioral processes enable us to adapt, survive, and flourish

psychology

the science of behavior and mental processes

psychometrics

the scientific study of the measurement of human abilities, attitudes, and traits

cohort

A population group unified by a specific common characteristic, such as age, and subsequently treated as a statistical unit

Introspection

a method of self-observation in which participants report their thoughts and feelings

Theory

aims to explain some phenomenon and allows researchers to create a hypothesis to collect data to support it

Hypothesis

A testable prediction, often implied by a theory

operational definition

a statement of the procedures used to define measurement of research variables

case study

a descriptive technique in which one individual or group is studied in depth in the hope of revealing universal principles

naturalistic observation

a descriptive technique of observing and recording behavior in naturally occurring situations without trying to manipulate and control the situation

survey

the collection of data by having people answer a series of questions

random sample

method of selecting from a population in which each person has an equal probability of being selected

population

a group from which a sample is selected

Correlation

A measure of the relationship between two variables

correlational coefficient

a number between -1 and +1 expressing the degree of relationship between two variables

Scatterplot

a graphed cluster of dots, each of which represents the values of two variables

illusory correlation

perception of a relationship where none exists, or perception of a stronger relationship than actually exists

dependent variable

The outcome factor; the variable that may change in response to manipulation

independent variable

The experimental factor that is manipulated; the variable whose effect is being studied.

experimental group

in an experiment, the group exposed to the treatment, that is, to one version of the independent variable

control group

in an experiment, the group not exposed to the treatment

random assignment

placing research participants into the conditions of an experiment in such a way that each participant has an equal chance of being assigned to any level of the independent variable

single-blind

study in which the subjects do not know if they are in the experimental or the control group

double-blind

A research strategy in which neither subjects nor experimenters know which subjects are in the experimental or control groups.

Hawthorne effect

A type of reactivity in which individuals modify or improve an aspect of their behavior in response to their awareness of being observed.

placebo effect

experimental results caused by expectations alone; any effect on behavior caused by the administration of an inert substance or condition, which the recipient assumes is an active agent.

confounding variable

a factor other than the independent variable that might produce an effect in an experiment

informed consent

an ethical principle that research participants be told enough to enable them to choose whether they wish to participate

Debriefing

the post-experimental explanation of a study, including its purpose and any deceptions, to its participants

standard deviation

a measure of variability that describes an average distance of every score from the mean

normal curve

A symmetrical, bell-shape that describes the distribution of many types of data; most scores fall near the mean (68 percent fall within one standard deviation of it) and fewer and fewer near the extremes.

inferential statistics

procedures used to draw conclusions about larger populations from small samples of data

statistical significance

The condition that exists when the probability that the observed findings are due to chance is very low.

p-value

In scientific research, this threshold (less than 0.05) is used as the standard cutoff to determine if an outcome is "statistically significant" and proves a genuine effect rather than by chance

falsifiable

possibility that a hypothesis or theory can be disproven by observation or experiment

replication

repeating the essence of a research study, usually with different participants in different situations, to see whether the basic finding extends to other participants and circumstances

social desirability bias

the tendency for people to say what they believe is appropriate or what they think the researcher expects

self-report bias

systematic errors that can occur in self-report data because participants are unable or unwilling to answer accurately

experiment

A research method in which an investigator manipulates one or more factors to observe the effect on some behavior or mental process

Quantitative Research

Research that provides data that can be expressed with numbers, such as ranks or scales.

Qualitative Research

research that relies on what is seen in field or naturalistic settings more than on statistical data

descriptive statistics

numerical data used to measure and describe characteristics of groups. Includes measures of central tendency and measures of variation.

Histogram

A graph of vertical bars representing the frequency distribution of a set of data.

mode

The value that occurs most frequently in a given data set.

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

skewed distribution

a representation of scores that lack symmetry around their average value

range

the difference between the highest and lowest scores in a distribution

meta-analysis

a "study of studies" that combines the findings of multiple studies to arrive at a conclusion

effect size

a measure of the strength of the relationship between two variables or the extent of an experimental effect

deductive reasoning

the process of applying a general statement to specific facts or situations

inductive reasoning

A type of logic in which generalizations are based on a large number of specific observations.

structionalism

an early school of psychology that aims to break down the human mind into its most basic, foundational components—such as sensations, feelings, and images—and analyze how they interact