Define information bias and give an example.

• A. Systematic error in measurement; example: recall bias in case-control studies
• B. Random sampling error due to small sample size
• C. Confounding due to an unmeasured variable
• D. Selection bias due to nonresponse

Answer: (A)

Information bias occurs when there is a systematic error in measuring or classifying information, such as exposure or outcome, leading to misclassification that distorts the true association. A classic example is recall bias in case-control studies, where cases may remember past exposures differently from controls, causing the observed link between exposure and disease to be biased in one direction or another. The other options describe different types of bias or error: random sampling error from a small sample size is about imprecision due to sampling, confounding is distortion from an unmeasured variable, and selection bias from nonresponse relates to who participates rather than how information is measured.