1. Define lead time
2. Define critical point
3. What complicates screening program?
4. What are methodological issues in assessing screening? (3)
1. Leadtime: interval by which timing of diagnosis is advanced by screening
2. Point in natural history before which treatment is more effective and/or less difficult to administer. If a disease is potential curable, its curable before this point, but not after. There can be multiple critical points.
3. Natural history of cervical cancer may not be progressive, can jump around, complicating things.
4. Selection bias (referral/volunteer bias, length-based sampling (prognostic selection), lead time bias