Why is self-reported exposure data a concern in cohort studies?

• A. It can lead to misclassification and recall bias, reducing validity.
• B. It provides objective measures of exposure.
• C. It has no impact on validity.
• D. It is always more accurate than administrative data.

Answer: (A)

Self-reported exposure data in cohort studies is limited by the accuracy of participants’ memories and willingness to report truthfully. People may forget, misremember, or tailor their reports to what they think is expected, leading to misclassification of who was truly exposed. This misclassification can bias the estimated association between exposure and outcome—often diluting real effects if misclassification is non-differential, or potentially exaggerating them if it is differential—thereby reducing the study’s validity. Using objective or validated exposure measurements minimizes these errors and yields more trustworthy results. While self-report can be informative in some contexts, it does not provide objective data and can—and often does—affect study validity.