Which bias is described as systematic differences between withdrawals from a study?

Which bias is described as systematic differences between withdrawals from a study?

• A. Attrition bias
• B. Recall bias
• C. Observer bias
• D. Selection bias

Answer: (A)

Systematic differences between participants who remain in a study and those who withdraw are attrition bias. In longitudinal research, people drop out for various reasons, and if those reasons relate to the exposure or outcome, the final sample may no longer represent the initial one, distorting the estimated effect. This threatens internal validity because results could be biased by who stayed versus who left. Recall bias involves inaccurate memory of past events; observer bias occurs when researchers’ expectations influence measurements; selection bias relates to how participants are chosen or allocated. So, attrition bias best fits the description.

Systematic differences between participants who remain in a study and those who withdraw are attrition bias. In longitudinal research, people drop out for various reasons, and if those reasons relate to the exposure or outcome, the final sample may no longer represent the initial one, distorting the estimated effect. This threatens internal validity because results could be biased by who stayed versus who left. Recall bias involves inaccurate memory of past events; observer bias occurs when researchers’ expectations influence measurements; selection bias relates to how participants are chosen or allocated. So, attrition bias best fits the description.