Question

***PLEASE label what answer is for what question as clear as possible**** (Yes this is ONE question)

Suppose 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. At the first screen, 1132 women were positive on the 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 in year of the screening test.

A. Fill in the two by two table showing these results.

B.  What is the prevalence of the detectable pre-clinical phase of breast cancer in this population?

C. Calculate and interpret the sensitivity and specificity of this new screening test.

D. Since computerized digital mammography is a new technique, the manufacturers must determine the appropriate “criterion of positivity.” Define the “criterion of positivity” and state how it influences the sensitivity and specificity.

E. Calculate and interpret the predictive value of a positive test result for this new screening test.

F. 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 low PV+?

G. How can you evaluate the effectiveness of a screening program that uses this new screening technique?

H. Define the term “lead time bias” and state what effect it has on the evaluation of a screening program.

I. Define the term “length bias” and state what effect it has on the evaluation of a screening program.

Answer 1