alleryStart learning →A cohort produced 16 new cases of heart disease over 6,400 person-years of observation. What is the incidence rate per 1,000 person-years?
A0.25 per 1,000 years
B7.6 per 1,000 years
C25.0 per 1,000 years
D2.5 per 1,000 years
Answer & Solution
Correct answer: D. 2.5 per 1,000 years
1. An incidence rate divides new cases by the total time the population was observed and at risk.
2. 16 divided by 6,400 equals 0.0025 cases per person-year.
3. Multiplying by 1,000 gives 2.5 cases per 1,000 person-years.
4. 7.6 per 1,000 comes from dividing 16 by the 2,100 women enrolled, which is the incidence proportion and ignores everyone lost to follow-up.
5. 0.25 applies a multiplier of 100 and 25.0 applies one of 10,000, so both misreport a correct division.
_Source: CDC Principles of Epidemiology in Public Health Practice (3rd ed., US federal, public domain), Lesson 3 "Measures of Risk", section Definition of incidence rate_
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