When participants drop out of a study, leading to a change in the nature of the sample, it would cause which of the following threats to internal validity?

ASelection threat

BAttrition threat ✓ Correct

CHistory threat

DTesting threat

Correct answer: (B) Attrition threat

Explanation

Dropout of participants that alters the sample is an attrition threat.

Attrition is also called experimental mortality in internal validity.

Selection threat comes from non-equivalent groups before the study begins.

History threat arises from outside events occurring during the study.

Testing threat stems from repeated measurement changing later scores.

Differential attrition across groups distorts comparison of outcomes.

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