As mortality has its data sources, so too does morbidity. Morbidity is defined in the fourth edition of The Dictionary of Epidemiology (New York: Oxford University Press; 2001:118), edited by John Last, as “any departure, subjective or objective, from a state of physiological or psychological well-being.” Epidemiologists generally feel more comfortable analyzing objective morbidity data, as captured in physician-diagnosed diseases, injuries, and disabilities, than subjective morbidity data as self-reported by individuals or reported on behalf of individuals by non-physician third parties.

Prominent morbidity data sources include disease registries, hospital emergency department and admission records, periodic health surveys, public and private health insurance records, and sickness-absence records for schools and workplaces.