Certified in Public Health (CPH) Practice Exam

Incidence density, while used to measure the occurrence of new cases of a disease in a particular population over time, is not a proportion. Instead, incidence density is expressed as a rate, usually per person-time units. This means it examines the number of new cases that occur in a population at risk during each moment in time, adjusting for the varying amount of time each individual is at risk. In contrast, cumulative incidence reflects a proportion by measuring the total number of new cases in a specified time period divided by the population at risk at the start of the time period. Prevalence, which combines incidence and duration, also serves as a measure of disease occurrence but is not a rate. Overall, understanding the definitions and calculations associated with these different epidemiological measures is crucial for interpreting public health data accurately.