A population-based mammography program identifies predominantly indolent, slowly progressive breast tumors because fast-growing tumors become symptomatic between screening rounds and are diagnosed outside the program. Screened women therefore appear to have better prognosis. This phenomenon is called:
- A Lead-time bias
- B Neyman's bias
- C Length bias ✓
- D Diagnostic suspicion bias
Correct answer: C. Length bias
Explanation
Length bias arises because screening is more likely to detect slow-growing lesions that remain detectable for long intervals, while aggressive tumors surface clinically between rounds. This inflates the apparent benefit of screening independent of any true therapeutic effect. Neyman's bias is incidence-prevalence bias due to missing fatal or recovered cases, and diagnostic suspicion bias concerns knowledge of exposure altering the intensity of diagnostic workup.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.