Imagine a population of 10,000 new army recruits. Your interest is in the incidence and prevalence of gunshot wounds on war duty. Assume all gunshot wounds lead to permanent visible damage. You follow...

Imagine a population of 10,000 new army recruits. Your interest is in the incidence and prevalence of gunshot wounds on war duty. Assume all gunshot wounds lead to permanent visible damage. You follow the recruits for one year. All of the study population survive, all medical records are available, and all are available for interview and examination. Assume that the occurrence of gunshot wounds is spread evenly through the year, and that at recruitment none had such a wound. Over the year you find that 20 recruits had a gunshot wound.

Calculate:

1. What is the cumulative incidence rate of gunshot wounds? What is the incidence rate based on the person-time denominator?


2. What is the point prevalence rate of having had a gunshot wound at the beginning, middle and end of the year?


3. What is the period prevalence rate over the year?


4. If the incidence rate remains the same over time, what is the prevalence rate of ever being scarred by the end of five years?


5. What is the average duration of a gunshot wound, among those scarred, by the end of the first year?


6. What is the estimate of the point prevalence over the five-year period?


7. What is the average duration of scarring over the five years?