AP Psych Week 2

Confounding variable

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

Operational definition

A carefully worded statement of the exact procedures (operations) used in research studies, such as defining human intelligence as what an intelligence test measures (also known as operationalization).

Control group

In an experiment, the group not exposed to the treatment.

Experimental group

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

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 and whose effect is being studied.

Dependent variable

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

Statistical significance

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

Single-blind experiment

An experimental procedure in which the research participants are ignorant (blind) about whether they have received the treatment or a placebo.

Double-blind experiment

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

Informed consent

Giving potential participants enough information about a study to enable them to choose whether they wish to participate.

Percentile rank

The percentile of scores that are lower than a given score.

Social desirability bias

Bias resulting from people responding in ways they presume a researcher expects or wishes.

Confirmation bias

A tendency to search for information that supports preconceptions and to ignore or distort contradictory evidence.

Experimenter bias

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

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).

Sampling bias

A flawed sampling process that produces an unrepresentative sample.

Convenience sampling

A non-probability research method where researchers select participants who are easily accessible, available, and close at hand rather than choosing them randomly.

Random sampling

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

Representative sample

A smaller group of participants that accurately reflects the demographics, characteristics, and key variables of a larger target population.

Standard deviation

A computed measure of how much scores vary around the mean.

Positive skew

A distribution shape where the tail extends to the right (really high values) and most scores are low.

Negative skew

A distribution shape where the tail extends to the left (lower values) and most scores are high.

Normal curve

A symmetrical, bell-shaped curve that describes the distribution of many types of data, where most scores fall near the mean (approximately $68\%$ fall within one standard deviation) and fewer scores lie near the extremes.

Outlier

A data point that diverges greatly from the overall pattern.

Mean

The arithmetic average of a distribution, obtained by adding the scores, then dividing by the number of scores.

Mode

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

Median

The middle score in a distribution; half the scores are above it and half are below it.

Measures of central tendency

Statistical summary values that describe the center point or typical score of a data set.

Validity

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

Reliability

The extent to which a test yields consistent results as assessed by the consistency of scores on two halves of the test, on alternative forms of the test, or on retesting.

Generalizability

The extent to which the findings of a research study can be applied or extended to the larger target population or real-world settings.

Institutional Review Board (IRB)

An administrative committee at a school or research center that reviews and approves psychology study plans before they begin to make sure human participants are protected.

Debriefing

The post-experimental explanation of a study, including its purpose and any deception, to its participants.

Deception

The deliberate practice of misleading research participants about the true purpose or procedures of an experiment.

Informed assent

A minor's or non-legally competent person's agreement to take part in a study, given in age-appropriate terms after a basic explanation, accompanied by formal parental informed consent.