Retrospective epidemiological studies are particularly susceptible to which type of bias?

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

Answer: (A)

Retrospective epidemiological studies gather exposure information after the outcome has occurred, often by asking participants to remember past events. Because memory can fade or be influenced by current health status or beliefs about what causes disease, the accuracy of recalled exposure tends to differ between groups. This differential recall creates recall bias, which can distort the apparent relationship between exposure and outcome in these studies. For example, people with a disease may be more likely to remember and report certain past exposures than people without the disease, exaggerating or underestimating associations.

While other biases can be present in retrospective designs, recall bias is the most characteristic and influential in this context—memory-driven misclassification of exposure is the central vulnerability of retrospective data.