Q4: A cohort of 10,000 individuals has been followed-up 10 years for occurrence of an event.

The incident rate was constant over the whole period. No subject is lost to follow-up.

Events 1813

Population 10,000

Person-years 90635

(a) Calculate the incidence risk, and the incident rate. (2pts)

(b) Lets suppose that some of the members of the cohort emigrate, and cannot be followed-up until the 10 years end. How would this incomplete follow-up affect the two measures? (2pts)

Lets assume that the same cohort is followed-up for 10 more years.

Events 3297

Population 10,000

Person-years 164850

(c) Calculate the risk, and the incident rate. (2pts)

(d) Comment on the possible differences between the estimates obtained after 10 years and 20 years of follow-up. (1pt)