A prospective cohort study was conducted to examine risk factors for a first str

Question

A prospective cohort study was conducted to examine risk factors for a first stroke among those who have never had a stroke. The study began on January 1, 2010 and lasted 6 years. The participation of 5 individuals in the study is shown in Figure 1, below.

Figure 1

Question 5 (use Figure 1) Calculate the number of person-years contributed to the study by the 5 individuals in Figure 1.

2010 2011 2012 2013 2014 2015 x x x x x x started at beginning
completed study x x x x x started at beginning
died 12/31/2014 x x x x started 1/1/2012
completed study x x x started 1/1/2011
lost to follow up 12/31/2013 x x x started at beginning
had stroke 12/31/2012

Explanation / Answer

Person-time is the sum of total time contributed by all subjects. The unit for person-time in this study is person years in this case.

So 6 + 5 + 4 + 3 + 3 = 21

21 is the total person years contributed to the study by 5 individuals

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