Epidemiology in History Snippets From the Past: Cohort Analysis of Disease Rates—Another Piece in a Seemingly Still Incomplete Puzzle

For almost a century, epidemiologists have stratified age-specific disease rates by year of birth to better under-stand the distribution of a disease in a population and its evolution across time. In the present article, I review the contributions of John Brownlee, Kristian Feyer Andvord, and Wade Hampton Frost and, to accentuate the similar-ities of their approaches, redraw their original graphs of age-specific death rates of tuberculosis organized either by year of death or year of birth. In addition, this article reports on an apparently universally forgotten publication in the American Journal of Hygiene published in 1929, which both upsets the conventional history of the earliest reports of disease rates stratified by birth cohorts and challenges the theory that Frost discovered cohort analysis indepen-dently and gave it its name. cohort analysis; tuberculosis; typhoid; vital statistics Age-specific incidence or mortality rates may tell a differ-ent story if organized by year of birth or by year of death. This seems trivial, right? The notions of age, period, and cohort effects have been in textbooks of epidemiology for at least 50 years (1). However, if we move back another 50 years, say to 1910, there are no obvious traces of these concepts