A cross-sectional study finds that regular aspirin users have a lower prevalence of cardiovascular disease compared to non-users (prevalence ratio 0.65). An epidemiologist argues this estimate may be biased because aspirin users who developed serious cardiovascular disease are less likely to be alive and thus not enrolled. This phenomenon is:
- A Confounding by indication
- B Healthy user bias
- C Neyman (survivor) bias ✓
- D Lead time bias
Explanation
Neyman bias (also called incidence-prevalence bias or survivor bias) occurs in prevalence studies when cases with a certain exposure either die or recover more rapidly, leading to under-representation of the exposure among prevalent cases. Here, aspirin users who developed fatal CVD are no longer in the cross-sectional sample, artificially lowering measured CVD prevalence among aspirin users. Healthy user bias (aspirin users tend to adopt other healthy behaviours) is also possible but the described mechanism is specifically survivor bias. Lead time bias applies to screening contexts.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.