What does internal validity measure in a study?

Internal validity is a crucial aspect of research design that measures the extent to which a study can establish a cause-and-effect relationship between independent and dependent variables within the context of the study. When internal validity is high, it indicates that the changes observed in the dependent variable can be attributed to the manipulation of the independent variable, rather than to other confounding variables or external factors.

For instance, if a study tests the effectiveness of a psychological intervention on reducing anxiety, high internal validity ensures that any observed reduction in anxiety is likely a result of the intervention rather than other factors like participant characteristics or concurrent events. This is essential for drawing accurate conclusions about the causal relationships within the scope of the research.

In contrast, the other options deal with different aspects of research methodology. Generalizability relates to external validity and how well the findings can be applied to other populations or settings. Replicability may refer to the consistency of results across different studies or over time, while the diversity of the participant pool pertains to the representativeness of the sample in relation to the broader population.