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
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