Lead-time bias in screening trials leads to an apparent increase in survival time. The best way to assess whether a screening programme truly reduces mortality from a disease is to measure:

• A 5-year survival rates in screened vs. unscreened populations
• B Disease-specific mortality rates (deaths/population) in screened vs. control populations ✓
• C Mean tumour size at diagnosis in screened vs. unscreened groups
• D Number of cases detected at early stage in the screened group

Explanation

Lead-time bias occurs when screening detects disease earlier in its natural history, thereby lengthening measured survival time even if the disease course is not actually altered. Survival (from diagnosis to death) is inflated by the 'lead time' (time gained by early detection). Disease-specific mortality rate (deaths per population per year) is unaffected by lead-time bias because it measures when people die relative to the population, not relative to diagnosis. RCTs measuring disease-specific mortality in screened vs. unscreened populations are the gold standard for proving screening effectiveness.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.