A cross-sectional study finds a prevalence odds ratio of 3.2 for obesity among adults with depression. The MAIN limitation of using prevalence (rather than incidence) data to study this association is:
- A Prevalence is affected by both incidence and disease duration, making causal directionality unclear ✓
- B Cross-sectional studies cannot calculate odds ratios
- C The sample size in cross-sectional studies is always too small
- D Depression cannot be measured objectively in cross-sectional designs
Correct answer: A. Prevalence is affected by both incidence and disease duration, making causal directionality unclear
Explanation
Prevalence = Incidence × Duration (Levin's formula). In a cross-sectional study, individuals with longer disease duration are over-represented, and associations may reflect duration effects rather than true incidence associations. Additionally, since both exposure and outcome are measured simultaneously, the temporal sequence needed to infer causality cannot be established.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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