Posted: February 24th, 2017
0. You are conducting a prospective study of hepatitis B virus (HBV) infection and its relation to liver failure. Normally, the immune system neutralizes the virus and most infected people are left with HBV antibodies but no detectable circulating virus. A small proportion of people who are infected with HBV remain with circulating virus itself (HBV viremic) and it is this group that is believed to be at high risk of liver failure. You put together a cohort study of 500 persons who are HBV viremic and 500 persons with HBV antibodies but who do not have detectable virus. You follow this cohort for five years. Among the first group that are HBV viremic, 50 persons develop liver failure: 5 at 10 months, 10 at 20 months, 20 at 36 months, 10 at 42 months, and 5 at 50 months. Among the second group that are HBV antibody positive but who do not have detectable virus (i.e., HBV non-viremic), 10 persons develop liver failure: 5 at 32 months and 5 at 55 months.
a. Calculate the person-time of follow up for each group. Show calculations. (6 pts)
b. Calculate the liver failure incidence rate for each group (i.e., HBV viremic and HBV non-viremic). Express each rate with an appropriate metric in the denominators. Show calculations. (6 pts)
c. How much of an increase of liver failure incidence is seen among persons with detectable HBV virus compared with those who have HBV antibodies but no detectable virus? Give results for absolute and relative differences of incidence. Show calculations. (6 pts)
d. Interpret each measure calculated in 10c above (one sentence each). (6 pts)
Place an order in 3 easy steps. Takes less than 5 mins.