Consider a closed population of 60,000 people who were followed for the development of a particular non-lethal chronic disease. At the start of follow-up on September 1, 2013, 700 persons were found to have the disease. During the three years of follow-up, the following data were obtained:
Year 1 300 were diagnosed with the disease, 15 died of other causes, 5 were lost to follow-up
Year 2 350 were diagnosed with the disease, 20 died of other causes, 0 were lost to follow-up
Year 3 325 were diagnosed with the disease, 40 died of other causes, 5 were lost to follow-up
Assume that the diagnoses, deaths, and losses to follow-up were uniformly distributed within their year of occurrence so that, on average, they can be considered to have occurred in the middle of the year.
a) Calculate the prevalence of the disease on August 31, 2014.
b) Calculate the one-year incidence proportion of the disease in Year 2, assuming no competing risks
c) Calculate the incidence rate of the disease over the three-year follow-up period