Which bias is less likely in a prospective cohort study because exposure is defined before outcome measurement?

• A. Information bias
• B. Confounding bias
• C. Recall bias
• D. Selection bias

Answer: (C)

The timing of exposure assessment matters for memory-based errors. In a prospective cohort, exposure status is established before any disease outcome occurs, so participants’ recollection of past exposures isn’t influenced by having the disease. This minimizes recall bias, which tends to distort results when cases remember exposures differently than non-cases after the outcome has appeared.

Other biases can still occur in cohort studies—for example, information bias from misclassifying exposure or outcome, selection bias from who enrolls or who is lost to follow-up, and confounding bias from other factors linked to both exposure and outcome—but recall bias is the one most diminished by assessing exposure before outcomes.