Misclassification bias is a form of information bias caused by which issue?

• A. A misclassification due to selection of subjects.
• B. Imperfect sensitivity or specificity of diagnostic tests leading to erroneous group assignment.
• C. Confounding due to unmeasured variables.
• D. Observer bias in outcome assessment.

Answer: (B)

Misclassification bias arises when the information about who truly has the disease or who was truly exposed is distorted by measurement error. If a diagnostic test isn’t perfect, some people with the disease are labeled non-diseased and some without the disease are labeled diseased. This wrong grouping comes from imperfect sensitivity (missing true cases) and imperfect specificity (false positives), and it alters the observed association between exposure and outcome. If the misclassification affects all groups equally (nondifferential), it tends to weaken the apparent relationship, pulling it toward the null. If it differs by outcome or exposure (differential), the bias can skew results in either direction.

Selection of subjects causes selection bias; confounding from an unmeasured variable distorts the effect; observer bias in outcome assessment is another form of information bias but relates to how outcomes are judged rather than misclassifying disease status due to test accuracy.