Janet Lane-Claypon (1877-1967), English physician and one of the founders of epidemiology. Lane-Claypon carried out the first retrospective cohort study when she investigated two groups of babies, one that was fed breast milk and one that was fed cow's milk. This study was also the first to use confounding, investigating whether any observed differences were due to factors other than the variables being studied. It was also the first to use a t test to analyse the data.