3. In the table below, the dashed lines illustrate the length of exposure (in we

Question

3. In the table below, the dashed lines illustrate the length of exposure (in weeks) of some health outcome among a group of 20 subjects. There were 7 new cases of the outcome reported during the observation period. These cases are not illustrated in the table. Answer the questions below in the context of this information. Subject Length of Exposure in Weeks Time@Risk 3.5 2.5 3.5 5,5 1.5 0.5 3.5 3.5 2.5 2.5 3.0 0.5 4.0 1.0 2.5 3.5 3.5 0.5 10 12 13 14 15 16 17 18 19 20-… What is the cumulative incidence over the study period (per 1,000)? a. b. What is the incidence density over the same study period (per 1,000)?

Explanation / Answer

a)

Cumulative incidence is the number of new cases in a specified period divided by the number of people at risk in the study population

Number of new cases in the specified period=7

Number of people in the study=20

Cumulative incidence=7/20=0.35

Per 1,000, rate is given by

0.35*1000=350

b) Incidence density is the number of new cases of a disease in a specified period divided by the sum of length of time at risk for each individual in the population

Total time at risk=55.5

Number of new cases=7

Incidence density=7/55.5=0.126

Per 1000,

0.126*1000=126

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