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1. Define screening
2. What type of distribution is ideal for screening?
3. What is less easy to interpret? What does this require?
1. Examination of asymptomatic people in order to classify them as likely or unlikely to have a certain disease
2. Bimodal (TB)
3. Unimodal (i.e., blood pressure) requires cutpoints which may change.
What are questions that need to be addressed in a screening test? (5 total)
1. How good is the test? (sensitivity/specificity in a population, PPV and NPV in a person)
- 2. Does finding disease earlier have any real value?
- - Does it decrease specific mortality?
- - Does it REALLY decrease mortality?
- - Is it cost-efefctive
1. Why do we screen? (4)
2. Why try to find people at risk of, but currently without, disease? (3)
3. When can a disease be detected?
1. To find asymptomatic people to cure disease, slow its progress, and prevent its spread OR to study the natural history of the disease.
2. To prevent disease altogether, to delay its onset, and to study precondition state
3. After biological onset of disease but before first symptoms appear (during detectable preclinical phase)
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
What are possible outcomes of a screening program? (4)