Internal validity

Internal validity

The extent to which the independent variable (IV) is the only possible explanation for the results shown for the dependent variable (DV).

Threats to internal validity

Factors that can undermine the confidence in the findings of an experiment.

History (in internal validity)

Events that occur between the measurements of the dependent variable in a repeated-measure design.

Maturation

Changes in participants that may affect the results over time, such as aging or development.

Testing

Practice effects that occur because measuring the DV changes the DV.

Reactive measures

Measurement techniques that may influence the outcomes, such as self-reported attitudes.

Non-reactive measures

Measurement techniques that are less likely to influence the outcomes, like using hidden cameras.

Instrumentation (or instrument decay)

Changes in the measurement of the DV that result from the measuring device or human error due to fatigue.

Statistical regression

The tendency for extreme scores to regress toward the mean on subsequent measurements.

Selection bias

When participants are chosen in such a way that the groups are not equivalent prior to the experiment.

Mortality (attrition)

If participants drop out of the study at different rates across treatment groups.

Interactions with selection

Systematic differences that arise due to varying selection based on maturation, history, or instrumentation.

Diffusion or imitation of treatment

Occurs when participants in one treatment group become aware of or imitate the treatment methods of another group.

External validity

The extent to which the results of an experiment can be generalized to and have relevance for settings, people, times, and measures other than those used in the experiment.