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 understand 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 similarities 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 independently and gave it its name.