Incidence Density A cohort study (hypothetical) was conducted to look at surviva
ID: 3272551 • Letter: I
Question
Incidence Density
A cohort study (hypothetical) was conducted to look at survival after experiencing a myocardial infarction (heart attack). Ten participants were followed for 3 years, resulting in the following table:
Follow-up Time (Months)
Event
3
Death
5
Censored
8
Death
12
Death
17
Censored
19
Censored
27
Death
32
Censored
36
Followed until end of study period
36
Followed until end of study period
3) Calculate the rates separately for each of the 3 years of follow-up.
(must show work)
Follow-up Time (Months)
Event
3
Death
5
Censored
8
Death
12
Death
17
Censored
19
Censored
27
Death
32
Censored
36
Followed until end of study period
36
Followed until end of study period
Explanation / Answer
Out of the 10 participants, we want the rate for death and censored cases.
For death, on an average 4 out of 10 or 0.4 of the participants died within 3 years.
Rate of death is (3+8+12+27)/4 months = 12.5 months before a death. Or, average follow up time before death is 12.5 months
Similarly for censored we get 0.4 probability of participant being censored and average follow up time for censored is : (5+17+19+32)/4 = 18.25 months