Question

A cohort study among people who use drugs examined the risk of acquiring HIV infection based on whether or not people reported sharing syringes.

(1). Among those who share syringes, the incidence of HIV was 5.38 per 100 person-years
(2). Among those who never share syringes, the incidence of HIV was 2.47 per 100 person-years

What is the risk difference between people who share syringes versus people who do not?

Answer 1

The risk difference of acquiring HIV between those who share syringes and those who do not is 2.91 per 100 person-years.

Step-by-step explanation:

The risk difference between people who share syringes and those who do not is calculated by taking the difference between the incidence of HIV in the two groups. The incidence among those who share syringes is 5.38 per 100 person-years, while the incidence among those who never share syringes is 2.47 per 100 person-years. Thus, the risk difference is 5.38 - 2.47 = 2.91 per 100 person-years. This result indicates that the additional risk incurred by sharing syringes is 2.91 cases of HIV per 100 person-years.