He went to work as a demonstrator for the physiologist Leonard Hill (father of the future statistician Austin Bradford Hill) at the London Hospital Medical College. Leonard Hill recalled, "By recognising the ability of a student with nothing behind him to show his worth and by appointing him my assistant I may claim to have started Greenwood on his career." While Greenwood made a good start in physiological research he was already drawn to statistics; his first paper in Biometrika appeared in 1904. After a period of study with Karl Pearson he was appointed statistician to the Lister Institute in 1910. There he worked on a wide range of problems, including a study of the effectiveness of inoculation with the statistician Udny Yule. In the First World War Greenwood first served in the Royal Army Medical Corps but then was put in charge of a medical research unit at the Ministry of Munitions. There he investigated the health problems associated with factory work, one result of which was an influential study of accidents which he produced with Yule. In 1919 Greenwood joined the newly created Ministry of Health with responsibility for medical statistics. He co-authored a number of papers (see publications) with Ethel Newbold during his tenure there (and wrote a touching obituary for her on her early death in 1933).[3] In 1928 he became the first professor of Epidemiology and Vital Statistics at the London School of Hygiene and Tropical Medicine where he stayed until he retired in 1945. He established a group of researchers, of whom the most important was Austin Bradford Hill. Greenwood played the same role in A. B. Hill’s career as Hill’s father had played in his.
Engaged in medical research. Has applied the statistical method to the elucidation of many problems of physiology, pathology, hygiene and epidemiology. Is the author, or joint author, of more than sixty papers dealing with these applications, including important contributions to the experimental study of epidemiology (Journ Hyg, 24, 1925, Greenwood and Topley; ibid, 25, 1926, Greenwood, Newbold, Topley and Wilson). Has done much to encourage and develop the use of modern statistical methods by medical laboratory investigators, and, as Chairman of the Medical Research Council's Statistical Committee, to secure the adequate planning and execution of field investigations.
Greenwood produced a large body of research, was the first holder of important positions in modern medical statistics and wrote extensively on the history of his subject, but as Austin Bradford Hill wrote in his obituary, "in the future, it may well indeed seem that one of his greatest contributions, if not the greatest, lay merely in his outlook, in his statistical approach to medicine, then a new approach and one long regarded with suspicion. And he fought this fight continuously and honestly—for logic for accuracy, for ‘little sums.’"
A statistical method invented by Major Greenwood in a statistical study of infectious diseases[9] is still used in present-day research. The Greenwood statistic was used to discover that there is some kind of order in the placement of genes on the chromosomes of living things[10] and this inspired a new look at epigenetics, which is now considered to be as important as genetics in how living organisms develop and evolve.
Cripps, L, Greenwood, M. and Newbold, E (1923). "A Biometric Study of the Inter-relations of `Vital Capacity' stature, stem length and weight in a Sample of Healthy Male Adults". Biometrika. 14: 3–4. doi:10.2307/2331816. JSTOR 2331816.
Greenwood, M.; Newbold, E (1923). "On the Estimation of Metabolism from Determination of Carbon Dioxyde Production and on Estimation of External Work from Respiratory Metabolism". J. Hygiene. 21: 3–4. doi:10.1017/s0022172400031624. PMC 2167379 .
Greenwood, M.; Newbold, E (1927). "Practical Applications of Statistics of Repeated Events, particularly to Industrial Accidents". J. Royal Stat. Society. 90: 487–547. doi:10.2307/2341203. JSTOR 2341203.
Major Greenwood. The natural duration of cancer. London, England: His Majesty’s Stationery Office, Reports on Public Health and Medical Subjects, No. 33. 1926
Major Greenwood. Epidemics and crowd-diseases: an introduction to the study of epidemiology. 1935
Major Greenwood. Medical statistics from Graunt to Farr: the Fitzpatrick lectures for the years 1941 and 1943. 1948
^Greenwood, Major (1926). "The natural duration of cancer". Reports on Public Health and Medical Subjects. 33. London: Her Majesty's Stationery Office: 1–26.
^Kaplan, Edward L. in a retrospective on the seminal paper in "This week's citation classic". Current Contents24, 14 (1983). Available from UPenn as PDF.
^Greenwood, Major (1946). "The Statistical Study of Infectious Diseases". Journal of the Royal Statistical Society. 109 (2): 85–110. doi:10.2307/2981176. JSTOR2981176. PMID20256635.
Anne Hardy; Eileen Magnello (2002) "Statistical methods in epidemiology: Karl Pearson, Ronald Ross, Major Greenwood and Austin Bradford Hill", 1900–1945 Soz Praventiv Med; 47(2): 80–89.