In longitudinal studies, what is a common threat to validity due to participants dropping out?

In longitudinal studies, what is a common threat to validity due to participants dropping out?

• A. Attrition
• B. Selection bias
• C. Instrument decay
• D. Experimenter bias

Answer: (A)

Attrition is when participants drop out of a study over time. In longitudinal designs, this loss of participants can threaten validity because those who leave the study may differ in important ways from those who stay, leading to biased estimates of trends or effects. If dropouts are related to the outcome or to key characteristics, analyses based only on remaining participants can overstate or understate true relationships, and the study loses statistical power as the sample shrinks. This is distinct from selection bias (bias in how participants are chosen at the start), instrument decay (measurement tools becoming less reliable over time), or experimenter bias (the researcher’s expectations influencing measurements). Mitigation includes retention efforts and statistical approaches that handle missing data, like methods assuming data are missing at random.

Attrition is when participants drop out of a study over time. In longitudinal designs, this loss of participants can threaten validity because those who leave the study may differ in important ways from those who stay, leading to biased estimates of trends or effects. If dropouts are related to the outcome or to key characteristics, analyses based only on remaining participants can overstate or understate true relationships, and the study loses statistical power as the sample shrinks. This is distinct from selection bias (bias in how participants are chosen at the start), instrument decay (measurement tools becoming less reliable over time), or experimenter bias (the researcher’s expectations influencing measurements). Mitigation includes retention efforts and statistical approaches that handle missing data, like methods assuming data are missing at random.