AP Psychology Research Methods & Statistics

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)

False consensus effect

the tendency to overestimate the extent to which others share our beliefs and behaviors

Illusory correlation

the perception of a relationship where none exists

Critical thinking

thinking that does not blindly accept arguments and conclusions; Rather, it examines assumptions, discerns hidden values, evaluates evidence, and assesses conclusions

Operational definition

A precise description of how the variables in a study will be manipulated or measured; For example, human intelligence may be operationally defined as what an intelligence test measures

Hypothesis

A tentative statement about the relationship between two or more variables; a testable prediction or question

Theory

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

Replication

repeating the essence of an research study, usually with different participants in different situations, to see whether the basic finding extends to other participants and circumstances; To repeat or duplicate a scientific study in order to increase confidence in the validity of the original findings

Case study

an intensive observation technique in which one person (or small group of individuals) is studied in depth, possibly in the hope of revealing universal principles

Survey

A questionnaire or interview designed to investigate the opinions, behaviors, or characteristics of a particular group

Naturalistic observation

observing and recording behavior in their natural setting without trying to manipulate and control the situation

Correlation/Correlation coefficient

a measure of the extent to which two factors vary together; and thus of how well either factor predicts the other. The correlation coefficient is the mathematical expression of the relationship, ranging from -1 to +1.

Random sample

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

Scatterplot/Scatter diagram

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

Experiment

A method of investigation used to determine cause-and-effect relationships by purposely manipulating one factor (independent variable) to produce change in another factor (dependent variable)

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-evauation studies.

Placebo effect

experimental results caused by expectations alone; any effect on behavior caused by the administration of an inert substance or condition, which is assumed to be an active agent; any change attributed to a person's beliefs and expectations rather than an actual drug, treatment, or procedure

Experimental condition

the condition of an experiment that exposes participants to the treatment, that is, to one version of the independent variable.

Control group/condition

the group that is not exposed to the independent variable and serves as a comparison for evaluating the effect of the treatment

Random assignment

assigning participants to experimental and control conditions by chance, thus minimizing preexisting differences between those assigned to the different groups (experimental method)

Independent variable

the experimental factor that is manipulated; the variable whose effect is being studied (treatment variable)

Dependent variable

the outcome factor; the variable that may change in response to manipulations of the independent variable (outcome variable)

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 the number of scores

Median

the middle score in a distribution; half the scores are above it and half the scores are below it; (Remember to order the scores first)

Range

A measure of variability; the highest score in a distribution minus the lowest score

Statistical significance

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

Culture

the enduring behaviors, ideas, attitudes, and traditions shared by a large group of people and transmitted from one generation to the next

Scientific Method

A set of assumptions, attitudes, and procedures that guide researchers in creating questions to investigate, in generating evidence, and in drawing conclusions

Empirical evidence

Verifiable evidence that is based upon objective observation, measurement, and/or experimentation

Variable

A factor that can vary, or change, in ways that can be observed, measured, or verified

Statistics

A branch of mathematics used by researchers to organize, summarize, and interpret data

Meta-analysis

A statistical technique that involves combining and analyzing the results of many research studies on a specific topic in order to identify overall trends

Descriptive research methods

Scientific procedures that involve systematically observing behavior in order to describe the relationship among behaviors and events

Pseudoscience

Fake or false science that makes claims based on little or no scientific evidence

Representative sample

A selected segment that very closely parallels the larger population being studied on relevant characteristics

Random selection

Process in which subjects are selected randomly from a larger group such that every group member has an equal chance of being included in the study (correlational research)

Correlational study

A research strategy that allows precise calculation of how strongly related two factors are to each other

Positive correlation

A finding that two factors vary systematically in the same direction, increasing or decreasing together

Negative correlation

A finding that two factors vary systematically in opposite directions, one increasing as the other decreases

Confounding (extraneous) variable

A factor or variable other than the ones being studied that, if not controlled, could affect the outcome of an experiment

Placebo

A fake substance, treatment, or procedure that has no known direct effects

Practice effect

Any change in performance that results from mere repetition of a task

Main effect

Any change that can be directly attributed to the independent (treatment) variable after controlling for other possible influences

Descriptive statistics

Mathematical methods used to organize and summarize data

Frequency distribution

A summary of how often various scores occur in a sample of scores. Score values are arranged in order of magnitude, and the number of times each score occurs is recorded.

Histogram

A way of graphically representing a frequency distribution; a type of bar chart that uses vertical bars that touch

Frequency polygon

A way of graphically representing a frequency distribution; frequency is marked above each score category on the graph's horizontal axis, and the marks are connected by straight lines

Skewed distribution

An asymmetrical distribution; more scores occur on one side of the distribution than on the other

Positively skewed distribution

Most of the scores are low scores

Negatively skewed distribution

Most of the scores are high scores

Symmetrical distribution

A distribution in which scores fall equally on both sides of the graph. The normal curve is an example of a symmetrical distribution

Measures of central tendency

A single number that presents some information about the "center" of a frequency distribution

Measure of variability

A single number that presents information about the spread of scores in a distribution

Standard deviation

A measure of variability; expressed as the square root of the sum of the squared deviations around the mean divided by the number of scores in the distribution

z score

A number, expressed in standard deviation units, that shows a score's deviation from the mean

Standard normal curve (Standard normal distribution)

A symmetrical distribution forming a bell-shaped curve in which the mean, median, and mode are all equal and fall in the exact middle

Inferential statistics

Mathematical methods used to determine how likely it is that a study's outcome is due to chance and whether the outcome can be legitimately generalized to a larger population

t-test

Test used to establish whether the means of two groups are statistically different from each other

Type I error

Erroneously concluding that study results are significante

Type II error

Failing to find a significant effect that does, in fact, exist

Population

A complete set of something-people, nonhuman animals, objects, or events

Sample

A subset of a population