THE NATIONAL ANIMAL HEALTH MONITORING-SYSTEM IN MICHIGAN .2. METHODOLOGICAL ISSUES IN THE ESTIMATION OF FREQUENCIES OF DISEASE IN A PROSPECTIVE-STUDY OF MULTIPLE DYNAMIC POPULATIONS

Procedures are proposed for the computation of disease frequency measures and of their associated variances from data collected through prospective study of multiple dynamic cohorts (herds) with a National Animal Health Monitoring System. Estimates of either the annual incidence density for a group of herds or the 1-month risk of disease can be calculated from the same within-herd measure of monthly incidence density. It is proposed that the choice of measure to be estimated depends on the intended use of the information. Risk estimates are appropriate for producers and clinical health professionals making decisions at the animal or herd level. Incidence density measures are appropriate for extrapolation to reference populations used for state- and regional-level decision-making. © 1990.