ABSTRACT
A disease is endemic when it occurs with predictable regularity in a population with only minor fluctuations in frequency pattern over time. A disease may be endemic at any level of occurrence, but the term hyperendemic is often used when a high proportion of animals are affected within a given geographic area or population. Time series analysis focuses on the detection, description, and measurement of patterns or periodicities from temporal disease occurrence data. The decomposition model assumes that patterns of disease occurrence reflect the influence of one or more of the following: long-term trend, seasonal fluctuation, and residual. Irregular variation reflects random or unpredictable variation in disease occurrence among individuals in a population. Cyclical and irregular variation may be associated with disease outbreaks. Seasonal fluctuations are regular changes in disease frequency with periods shorter than a year that are usually related to known factors such as rainfall, month of the year, temperature, and timing of production events.
