Screening programmes detect a disproportionate number of slowly progressing, indolent tumours and miss rapidly progressing aggressive ones. This distortion of apparent screening benefit is known as:
- A Lead-time bias
- B Berkson's bias
- C Length bias ✓
- D Ascertainment bias
Correct answer: C. Length bias
Explanation
Because slow-growing tumours remain in the detectable preclinical phase longer, any screening test performed at intervals is more likely to catch them, while fast-growing cancers present symptomatically between screens. Screen-detected cases therefore have inherently better prognosis independent of treatment benefit, inflating apparent efficacy; this is length bias. Lead-time bias concerns earlier diagnosis timing, not growth rate, and Berkson's bias is admission-rate selection bias.
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.