Exam 3 Study Guide: Experimental Design and Validity

Vocabulary flashcards covering experimental design, internal validity threats, obscurement variables, and factorial designs from Chapters 10, 11, and 12.

Manipulated Variable

A variable in an experiment whose levels are assigned by the researcher; typically serves as the independent variable.

Measured Variable

A variable in an experiment whose levels are recorded rather than assigned; typically serves as the dependent variable.

Confounding Variable

A second variable that varies systematically with the independent variable, offering an alternative explanation for results and threatening internal validity.

Control Variable

A potential confounding variable that is held constant throughout an experiment.

Systematic Variability

Variability that lines up directly with the levels of the independent variable, creating a confound.

Unsystematic Variability

Random variability occurring across experimental conditions that is considered noise rather than a confound.

Selection Effect

An internal validity threat occurring when participants in one group are systematically different from those in another group at the beginning of an experiment.

Independent-Groups Design

An experimental design where different participants experience each level of the independent variable (also known as a between-subjects design).

Posttest-Only Design

An experimental design where the dependent variable is measured only once, following the manipulation.

Pretest/Posttest Design

An experimental design where the dependent variable is measured both before and after the manipulation to track change and verify group equality.

Within-Groups Design

An experimental design in which the same participants experience every level of the independent variable.

Repeated-Measures Design

A within-groups design where participants experience conditions one after another, with the dependent variable measured after each condition.

Concurrent-Measures Design

A within-groups design where participants are presented with all levels of the independent variable at the same time, and a single choice or preference serves as the dependent variable.

Counterbalancing

The practice of presenting conditions in different orders to different participants to distribute order effects evenly across all conditions.

Order Effect

An internal validity threat in within-groups designs where exposure to an earlier condition alters participant reactions to a subsequent condition.

Maturation Threat

An internal validity threat characterized by changes in participants that occur naturally over time rather than from the experimental manipulation.

History Threat

An internal validity threat that occurs when an outside event happening during the study causes the observed change.

Regression to the Mean

An internal validity threat where extreme scores on an initial test naturally move closer toward the average upon retesting.

Attrition Threat

An internal validity threat that arises when there is a systematic change in which participants drop out versus remain in a study.

Testing Threat

An internal validity threat wherein participant scores change simply as a result of taking a test more than once.

Instrumentation Threat

An internal validity threat that occurs when the measuring instrument or coding standards change over time rather than the participants changing.

Observer Bias

An internal validity threat where the expectations of researchers influence what they perceive or record.

Demand Characteristics

Cues in an experiment that lead participants to guess the research hypothesis and alter their behavior accordingly.

Placebo Effect

A response that occurs when participants improve simply because they believe they are receiving an active treatment.

Double-Blind Study

An experimental study design where neither the participants nor the researchers and observers know which condition each participant is assigned to.

Null Effect

A research outcome where a study fails to demonstrate a meaningful effect of the independent variable on the dependent variable.

Manipulation Check

An extra measure administered to confirm that the experimental manipulation functioned as intended.

Interaction Effect

An effect occurring in designs with multiple independent variables where the effect of one independent variable depends on the level of another independent variable.

Crossover Interaction

An interaction pattern where the effect of one independent variable reverses across levels of another, visually indicated by lines crossing in an X on a line graph.

Spreading Interaction

An interaction pattern where the effect of an independent variable is strong at one level of another independent variable and weak or absent at another, visually indicated by nonparallel lines that do not cross.

Factorial Design

An experimental setup involving two or more independent variables (factors) where every combination of their levels is tested.

Main Effect

The overall effect of one independent variable on the dependent variable, averaging across the levels of the other independent variable.

Mixed Factorial Design

A factorial design in which at least one independent variable varies between participants and at least one independent variable varies within participants.