1. A breast cancer screening program based on repeat free clinical breast examinations was implemented in a developing country for women aged 50-59 years. The program is open to all eligible women, but not compulsory. 
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3. a. Do you expect the incidence among the women who take advantage of the program to be the same as for the total eligible population? Why? In women who choose to take advantage of the program, the average annual incidence of previously undetected breast cancer is found to be about 100 per 100,000 on follow-up. In the first exam, point prevalence is found to be approximately 200 per 100,000. Assume that, after cases are confirmed by biopsy, no false negatives go undetected. 
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5. b. What is the average duration of the detectable preclinical phase in cases of breast cancer detected at the first exam? 
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7. c. Define lead time bias in the context of the evaluation of a screening program or procedure. 
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9. d. How does lead time bias affect the estimation of average survival time?