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A study of prostate cancer was initiated in the beginning of January 2015. One-thousand (1,000) men,...

A study of prostate cancer was initiated in the beginning of January 2015. One-thousand (1,000) men, 55-64 years of age, with no prior evidence of prostate cancer were enrolled in this study. The men were then followed by the investigators for four years until the end of the 2018. Each year during the study, the men were examined and tested for the presence of prostate cancer. The results of the annual examinations revealed the following: 10 cases were confirmed after 1 year 15 additional cases were confirmed after 2 years 20 additional cases were confirmed after 3 years 25 additional cases were confirmed after 4 years What was the total number of person-years for this study? What is the person-time incidence rate of prostate cancer in this group?

Math   Statistics-And-Probability   
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Answer #1

Number of Persons at risk for 1 year = 10

Number of Persons at risk for 2 years = 15

Number of Persons at risk for 3 years = 20

Number of Persons at risk for 4 years = 1000 - (10 + 15 + 20) = 955

Total number of person-years for this study = 1 * 10 + 2 * 15 + 3 * 20 + 4 * 955 = 3920 person-years

Number of prostate cancer cases in the study = 10 + 15 + 20 + 25 = 70

Person-time incidence rate of prostate cancer = Number of prostate cancer cases in the study / Total number of person-years for this study

= 70 / 3920

= 0.01785714 per person-year

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