AP Psychology Unit 2 Terms & Definitions

Hindsight Bias

Hindsight Bias

the tendency to believe, after learning an outcome, that one would have foreseen it. (Also known as the I-knew-it-all-along phenomenon.)

Theory

an explanation using an integrated set of principles that organizes observations and predicts behaviors or events.

Hypothesis

a testable prediction, often implied by a theory.

Operational Definition

a carefully worded statement of the exact procedures (operations) used in a research study. For example, human intelligence may be operationally defined as what an intelligence test measures.

Replication

repeating the essence of a research study, usually with different participants in different situations, to see whether the basic finding can be reproduced.

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 or control the situation.

Survey

a descriptive technique for obtaining the self-reported attitudes or behaviors of a particular group, usually by questioning a representative, random sample of the group.

Sampling Bias

a flawed sampling process that produces an unrepresentative sample.

Population

all those in a group being studied, from which samples may be drawn. (Note: Except for national studies, this does not refer to a country's whole population.)

Random Sample

a sample that fairly represents a population because each member has an equal chance of inclusion.

Correlation

a measure of the extent to which two factors vary together, and thus of how well either factor predicts the other.

Correlation Coefficient

a statistical index of the relationship between two things (from -1.00 to +1.00).

Variable

anything that can vary and is feasible and ethical to measure.

Scatterplot

a graphed cluster of dots, each of which represents the values of two variables. The slope of the points suggests the direction of the relationship between the two variables. The amount of scatter suggests the strength of the correlation (little scatter indicates high correlation).

Illusory Correlation

perceiving a relationship where none exists, or perceiving a stronger-than-actual relationship.

Regression Toward the Mean

the tendency for extreme or unusual scores or events to fall back (regress) toward the average.

Experiment

a research method in which an investigator manipulates one or more factors (independent variables) to observe the effect on some behavior or mental process (the dependent variable). By random assignment of participants, the experimenter aims to control other relevant factors.

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; contrasts with the experimental group and serves as a comparison for evaluating the effect of the treatment.

Random Assignment

assigning participants to experimental and control groups by chance, thus minimizing preexisting differences between the different groups.

Double-Blind Procedure

an experimental procedure in which both the research participants and the research staff are ignorant (blind) about whether the research participants have received the treatment or a placebo. Commonly used in drug-evaluation studies.

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.

Independent Variable

in an experiment, the factor that is manipulated; the variable whose effect is being studied.

Confounding Variable

a factor other than the factor being studied that might influence a study's results.

Dependent Variables

in an experiment, the outcome that is measured; the variable that may change when the independent variable is manipulated.

Validity

the extent to which a test or experiment measures or predicts what it is supposed to.

Informed Consent

giving potential participants enough information about a study 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.

Descriptive Statistics

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

Histogram

a bar graph depicting a frequency distribution.

Mode

the most frequently occurring score(s) in a distribution.

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.

Standard Deviation

a computed measure of how much scores vary around the mean score.

Normal Curve (normal distribution)

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

Inferential Statistics

numerical data that allow one to generalize to infer from sample data the probability of something being true of a population.

Statistical Significance

a statistical statement of how likely it is that an obtained result occurred by chance.