HW3: Cohort Studies

Scenario A: For True/False Questions 8 and 9

A study published in the American Journal of Public Health investigated the HIV infection among prisoners in Nevada. Of 1,105 prison inmates who were tested for HIV at the start of the study, 36 were found to be currently infected. All uninfected persons were then followed for a total of 1,207 person-years and retested for HIV upon release from prison. Two of the initially uninfected inmates demonstrated evidence of new HIV infection contracted in prison.

Scenario B: For Multiple Choice Questions 13 - 19

A cohort study enrolled 156 first heart attack survivors, all of whom were regular smokers up to the time of their first heart attack.  Each participant was followed for the entire 5 year study period (no loss to follow-up). 75 participants continued to smoke during the study period, and 81 quit smoking immediately after their first heart attack. 27 of those who continued to smoke died, and 14 of those who quit smoking died.

Scenario C: For Multiple Choice Questions 20 - 24

In a cohort study, 40,000 white males aged 25-39 years residing in Chicago having different levels of cholesterol at enrollment in 1967 were followed through 1992. Twenty-six coronary heart disease (CHD)-related deaths occurred during 36,581 PY of follow-up among men with elevated cholesterol. Fourteen CHD-related deaths occurred during 68,239 PY of follow-up among men with normal cholesterol.

Scenario D: For Multiple Choice Questions 25 - 28

Data pertaining to the frequency of occupational asthma (OA) among workers in an adhesive manufacturing facility are shown below. All workers in the facility were tested for new cases of OA at the start of the study and during two subsequent examinations carried out three years apart. The number of new OA cases was used to determine the incidence.

Jobs involving direct exposure to adhesives: 1,500 person years, 10 new cases of OA

Jobs with no direct exposure to adhesives: 6,000 person years, 20 new cases of OA