This threat to internal validity refers to participant dropout rates that could differ across conditions.

This threat to internal validity refers to participant dropout rates that could differ across conditions.

• A. Attrition
• B. History effects
• C. Maturation
• D. Selection bias

Answer: (A)

Attrition refers to participants dropping out of a study, and when dropout rates differ across conditions, it threatens internal validity. If more people leave one group than another, the groups that remain may no longer be comparable, so observed differences in outcomes could reflect who stayed rather than the effect of the intervention. This differential attrition can bias results, making it unclear whether any change is due to the manipulation or to the characteristics of those who continued. For example, if more participants drop out from the treatment group because the intervention is too demanding, the remaining participants may skew toward those who tolerate it better, exaggerating or masking the true effect. History effects would involve external events affecting groups during the study, maturation refers to natural changes over time within participants, and selection bias concerns preexisting differences due to nonrandom assignment; none of these specifically capture the problem of unequal dropout across conditions.

Attrition refers to participants dropping out of a study, and when dropout rates differ across conditions, it threatens internal validity. If more people leave one group than another, the groups that remain may no longer be comparable, so observed differences in outcomes could reflect who stayed rather than the effect of the intervention. This differential attrition can bias results, making it unclear whether any change is due to the manipulation or to the characteristics of those who continued. For example, if more participants drop out from the treatment group because the intervention is too demanding, the remaining participants may skew toward those who tolerate it better, exaggerating or masking the true effect. History effects would involve external events affecting groups during the study, maturation refers to natural changes over time within participants, and selection bias concerns preexisting differences due to nonrandom assignment; none of these specifically capture the problem of unequal dropout across conditions.