Janet Elizabeth Lane - Claypon (1877 – 1967) was an English physician. She was one of the founders of the science of epidemiology, pioneering the use of so-called cohort studies and case - control studies.

Born into an affluent Lincolnshire family, she was privately educated and entered the London School of Medicine for Women in 1898. A brilliant student, she won various honours, fellowships and degrees, including both an MD and PhD (making her an exceptionally early example of the "Doctor - doctor" phenomenon only now becoming common in modern medicine). By 1910, Lane - Claypon had acquired student honors, distinctive fellowships, and a string of degrees, including a doctorate in physiology and an M.D. She first put these skills to work in the research lab, investigating the biochemistry of milk and aspects of reproductive physiology, including, importantly, the structure and function of the ovary and the hormonal control of lactation. In 1912, Lane - Claypon published a ground breaking study of two cohorts (groups) of babies, fed cow's milk and breast milk respectively. Lane - Claypon found that those babies fed breast milk gained more weight, and she used statistical methods to show that the difference was unlikely to occur by fluke alone. She also investigated whether something other than the type of milk could account for the difference, an effect known as confounding. She moved from the lab to the arena of public health, where she grappled with a variety of maternal and child health issues. She became an advocate for breast feeding, as well as for the reform of midwife training and prenatal services, with a view to reducing the number of premature births and stillbirths and the rate of maternal mortality.

Having demonstrated the power of cohort studies, Lane - Claypon went on to develop another key type of epidemiological investigation, the so-called case - control study. In 1923, the Minister of Health, Neville Chamberlain, set up a committee to look into the “causation, prevalence and treatment of cancer” and to advise the ministry on the best way to investigate these problems. Lane - Claypon was hired to review the existing literature on breast cancer with an emphasis on its surgical treatment (primarily radical mastectomies). The committee then commissioned her to undertake a larger study “with a sufficient and suitable series” of women with breast cancer histories and “a parallel and equally representative series of control cases,” that is, “women whose conditions of life were broadly comparable to those of the cancer series but who had no sign of cancer”.

Lane - Claypon tracked down 500 women with a history of breast cancer - the “cases” - and compared them with 500 women who were free of the disease but otherwise broadly similar, known as “controls”. No large - scale review of this kind had ever been undertaken. Lane - Claypon realized that to generate a sufficient number of cases and controls — 500 in each category — she would need to enlist the support of several hospitals. Ultimately, six London and three Glasgow hospitals contributed data to the study, much of it apparently gathered under the supervision of other women physicians. Cases were defined as either recent or currently treated patients with breast cancer. Controls, women with no current or past histories of cancer, were drawn from inpatient and outpatient services of the hospitals supplying the cases. To demonstrate their comparability, Lane - Claypon evaluated both groups with respect to several variables, including occupation and infant mortality (both taken as proxies for social status), nationality, marital status, and age.

The detailed survey that emerged constituted, as far as we know, the first published epidemiological questionnaire. Among the more than 50 questions it asked were several relating to the respondents' reproductive health histories. This yielded results that enabled Lane - Claypon to identify many of the risk factors for breast cancer that are still considered valid today. Her conclusions (or her data reworked by later researchers) agreed with those of modern reviewers: breast cancer was associated with age at menopause, artificial menopause, age at first pregnancy (age at marriage used as a proxy), number of children, and lactation.

In 1926, the Ministry of Health published another of Lane - Claypon's report that is now considered the first “end results” study. It followed a large sample of women with pathologically confirmed breast cancer for up to 10 years after their surgery. The study confirmed that women who were surgically treated at an early stage of the disease had a much better chance of surviving three, five, or 10 years longer than those operated on at any later stage. She showed that breast cancer risk increased for childless women, women who married later than average, and women who did not breast feed. The overall breast cancer risk decreased according to the number of children. For all cases, rapid treatment held the key to survival among women with breast cancer. Woven through all of these reports are her concerns about the drawbacks and uncertainties that her own methodology exposed. Sidebar discussions reveal an extraordinarily rigorous and subtle intelligence at work. In the end - results study just mentioned, Lane-Claypon acknowledges the difficulties involved in deriving an accurate staging of the disease (in the days before routine diagnostic biopsies). She understood that differences in access to health care (and hence to surgical treatment) would influence survival results. She recognized the problems of bias created by limiting the study to survivors and by relying on the recall of breast cancer patients themselves rather than observing (with greater neutrality and potentially greater accuracy) the experience of newly diagnosed women going through treatment and beyond. Finally, in reviewing the family histories of her cases, she anticipated the role that genes might play in the development of breast cancer. “There appear to be some families,” she wrote, “in which for reasons not certain at present, cancer plays havoc with the members, and there is (some) slight evidence in some instances that it attacks the same organs.”