Question

Question 16

1. Imagine that exactly 5 years ago, a team of epidemiologists identified a study population of 4,500 men, 65-74 years, in Cedar Rapids, Iowa, to determine the incidence (or risk) of prostate cancer. Initial tests indicated that 515 of the men already had prostate cancer (and therefore not at risk). The remaining men were followed for 5 years to determine the cumulative incidence of prostate cancer. By the end of the follow-up, 156 men had developed prostate cancer. What was 5-year cumulative incidence?

   		37 new cases of prostate cancer per 1,000 men over the 5-year study
   		38 new cases of prostate cancer per 1,000 men over the 5-year study
   		39 new cases of prostate cancer per 1,000 men over the 5-year study
   		40 new cases of prostate cancer per 1,000 men over the 5-year study
   		41 new cases of prostate cancer per 1,000 men over the 5-year study

Question 17

1. Imagine that a study of prostate cancer was initiated in Des Moines, Iowa. A total of 1,000 men, 55-64 years of age, with no prior evidence of prostate cancer were enrolled in a 4 year study. Each year during the study, the men being observed were examined and tested for presence of prostate cancer. The results of annual examinations revealed:
   20 cases confirmed at 1^st
   exam
   25 additional cases at 2^nd
   exam
   40 additional cases at 3^rd
   exam
   45 additional cases at 4^th
   (final) exam
   What is incidence density of prostate cancer in this group?

   		18 new cases of prostate cancer per 1,000 person-years in the study
   		34 new cases of prostate cancer per 1,000 person-years in the study
   		37 new cases of prostate cancer per 1,000 person-years in the study
   		42 new cases of prostate cancer per 1,000 person-years in the study
   		105 new cases of prostate cancer per 1,000 person-years in the study

Answer 1

Total number of men to be surveyed = 4500

Existing patients of prostate cancer = 515

so, the revised sample becomes = 4500 - 515 = 3985

Number of men exposed to prostate cancer in 5 years = 156

Number of new cases in 5 years = 156/3985 = 0.0391468

Number of new cases per 1000 men in 5 years = 0.0391468*1000 = 39

hence the correct answer is : 3 that is, 39 new cases of prostate cancer per 1,000 men over the 5-year study

initial sample size = 1000

1st stage: 20 cases are confirmed

that is 20 cases per 1000 men

Revised sample size after 1st stage = 1000 - 20 = 980

2nd stage: 25 cases are confirmed

that is 25 cases per 980 men

Revised sample size after 2nd stage = 980 - 25 = 955

3rd stage: 40 cases are confirmed

that is 40 cases per 965 men

Revised sample size after 3rd stage = 965 - 40 = 925

4th stage: 45 cases are confirmed

that is 45 cases per 925 men

The actual ratio of cases become = 20/1000 + 25/980 + 40/965 + 45/925 = 0.13711

Cases per 1000 per year = (0.13711*1000)/4 = 137.11/4 = 34

correct answer is : 34 new cases of prostate cancer per 1,000 person-years in the study