Psychology Terms & Definitions: AP® Course Unit 0 Study Set

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. (Also known as operationalization.)

case study

a non-experimental technique in which one individual or group is studied in depth in the hope of revealing universal principles.

survey

a non-experimental 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.

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 variables (from −1.00 to +1.00).

variable

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

illusory correlation

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

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.

random assignment

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

independent variable

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

confounding variable

in an experiment, a factor other than the factor being studied that might influence a study’s results.

experimenter bias

bias caused when researchers may unintentionally influence results to confirm their own beliefs.

validity

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

descriptive statistics

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

histogram

a bar graph depicting a frequency distribution.

percentile rank

the percentage of scores that are lower than a given score.

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

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 scores lie near the extremes. (Also called a normal distribution.)

inferential statistics

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

meta-analysis

a statistical procedure for analyzing the results of multiple studies to reach an overall conclusion.

statistical significance

a statistical statement of how likely it is that a result (such as a difference between samples) occurred by chance, assuming there is no difference between the populations being studied.

effect size

the strength of the relationship between two variables. The larger the effect size, the more one variable can be explained by the other.