Principles of Diagnostic Testing Series
Part 3 – Population characteristics: Prevalence
Prevalence is an estimation of an individual’s risk of having a disease at a specific point in time. Apparent prevalence, or the proportion of test-positive individuals at a specific point in time, is found after performing a diagnostic test. Apparent prevalence may be misleading because it does not account for potential misclassification of disease due to testing errors. To determine the true prevalence or the proportion of diseased individuals in a population, the sensitivity and specificity of the diagnostic test must be considered. Diagnostic sensitivity is the proportion of individuals with the disease that test positive. Diagnostic specificity is the proportion of individuals without the disease that test negative.
The true prevalence accounts for errors from the diagnostic test and better estimates the actual prevalence of the disease in a population.