In a cancer screening programme, a pathologically slow-growing tumour is more likely to be detected than an aggressive fast-growing one. This preferential detection of clinically indolent disease is termed:

• A Lead time bias
• B Length time bias (sojourn-time bias) ✓
• C Overdiagnosis bias
• D Volunteer bias

Explanation

Length time bias (sojourn-time bias) arises because screening intervals are more likely to detect tumours with a long sojourn time (slow-growing) than those with a short sojourn time (aggressive tumours that present symptomatically between screens). Overdiagnosis is a related but distinct concept — the detection of tumours that would never have caused symptoms in the patient's lifetime. Lead time bias refers to earlier detection shifting the apparent survival curve without changing prognosis. Volunteer bias refers to self-selection by healthier individuals into screening programmes.

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

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