[A computer program to calculate expected cases in a dynamic cohort]

ECIDC (Expected Cases in Dynamic Cohorts) is a new interactive computerized programme in English for personal computers, created specifically to calculate expected cases in prospective cohort studies. Programmes available up to now have calculated the denominators of measurements of frequency, expressed in person-years, using the recruitment date and exit date of each individual in the cohort. ECIDC, instead, calculates directly the number of expected cases, recognizing only the date of recruitment. The programme considers the aging of the cohort, estimates the effect due to competitive mortality and eliminates the expected deaths. Then, it calculates the expected cases by applying incidence or specific mortality from the reference population. ECIDC considers the period effects of both competitive mortality and expected incidence. When observed reference data is lacking, it compiles estimates of age-specific incidence and/or mortality trends. ECIDC can be used in power calculation for the cohort study. It also can be applied to simulation studies of incidence and mortality trends. The present paper tries out various simulations and shows the potential of the computerized programme.