Screening – Chapter 16 – Homework AssignmentSuppose that 50,000 women who have never had a breast cancer diagnosis are available and willing to participate in a new screening program of computerized digital mammography. One thousand one hundred thirty-two (1132) women had a positive screening test. All of these positive women had a breast biopsy, and 136 were diagnosed with breast cancer. Of the 48,868 who screened “negative” on the test, 24 were in fact in the detectable pre-clinical phase. This was determined by following these women and observing that all 24 were diagnosed with breast cancer within one year of the screening test. 1. What is the prevalence of the detectable pre-clinical phase of breast cancer in this population?a. 136/50,000b. 160/50,000c. 1,132/50,0002. What is the sensitivity of this new screening test?a. 12%b. 85%c. 98%d. 99.9%3. What is the specificity of this new screening test?a. 12%b. 85%c. 98%d. 99.9%4. What is the predictive value of a positive test result for this new screening test?a. 12%b. 85%c. 98%d. 99.9%5. A colleague in another city reports that the same screening test (with the same sensitivity and specificity) is achieving a predictive value positive of only 6%. What is the explanation for this?a. The colleague is screening a higher risk population.b. The colleague is screening a lower risk population.c. The colleague is screening a larger population.d. The colleague is screening a smaller population.6. Lead time bias makes it erroneously appear that survival is better for screened versus unscreened cases.a. Trueb. False
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Introduction:
This assignment pertains to screening for breast cancer using a new computerized digital mammography technique. The data provided includes the number of women screened, the number of positive screenings, the number of breast biopsies, and the number of actual breast cancer diagnoses. The assignment aims to test the student’s understanding of the different aspects of the screening technique, including prevalence, sensitivity, specificity, predictive value, and lead time bias.
1. The prevalence of the detectable pre-clinical phase of breast cancer in this population is 24/50,000, as 24 out of the 50,000 women who were screened were diagnosed with breast cancer within a year.
2. The sensitivity of this new screening test is 98%, as 136 out of the 139 total breast cancer cases (1132 positive screenings and 24 pre-clinical cases) were detected by the test.
3. The specificity of this new screening test is 99.9%, as 48,844 out of the 48,868 women who screened negative did not have breast cancer.
4. The predictive value of a positive test result for this new screening test is 10.7%, as 136 out of the 1132 women who tested positive actually had breast cancer.
5. The explanation for the colleague’s screening test achieving a predictive value positive of only 6% could be that the colleague is screening a lower risk population.
6. True. Lead time bias can make it appear that survival is better for screened cases as they are diagnosed earlier, but this does not necessarily mean they will live longer.
