Screening

What makes a good screening programme and its biases: lead time, length and overdiagnosis.

5 pages

Measure

• Evaluating a screening programmeA screening programme is judged by how many people it reaches, what it finds and, above all…

Bias

• Lead-time biasScreening moves the date of diagnosis earlier; survival looks longer even if the person dies on…
• Length-time biasScreening mostly finds slow cases, which spend longer without symptoms and already had a better…
• OverdiagnosisOverdiagnosis is diagnosing a real disease that would never have caused symptoms or death in…

Concept

• Principles of screeningScreening looks for disease in people without symptoms; it is worth it only if the benefit is…

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← Epidemiology, biostatistics and public health

Educational content on epidemiological and statistical methods; the examples use made-up numbers to teach the calculation. Not a clinical or legal guide: current Colombian rules are in the official sources.

Representative model, for educational purposes only.