Vignettes of the history of epidemiology: Three firsts by Janet Elizabeth Lane-Claypon

In 1912, Janet Elizabeth Lane-Claypon, a British medical scientist 35 years of age who had already contributed substantial research findings in the fields of reproductive physiology and the bacteriology and biochemistry of milk, reported the results of a retrospective cohort study of weight gain during the first year of life among 204 infants fed boiled cows' milk compared with 300 infants fed human breast milk. The results of her investigation revealed that, up to the age of 208 days, breastfed infants gained more weight than infants fed boiled cows' milk. After that time period, weight gain was equal in the two groups. Lane-Claypon described, discussed, and analyzed her data for the possibility that her findings were due to sampling variation or confounding, and she used Student's t test to evaluate observed differences in weight gain in small subsets of the study population. As far as is known, this was the first use of the retrospective (historical) cohort design and the t test in an epidemiologic study.