Biographical Memoirs Volume 56 (1987) / Chapter Skim
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William Gemmell Cochran
William Gemmell Cochran
Pages 60-89
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Go Gem
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The family, consisting of Thomas, his wife icannie, and sons Oliver and William, moved to Gourock, a hol iciay resort town on the Firth of Clyde, when William was six, and to Glasgow ten years later. Oliver has colorful recollections of their childhood.
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Later, studying and reading became primary. His scholastic prowess won him many books as prizes and created an extensive home library.
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The emphasis in applied statistics at Iowa was then on sample surveys anct experimental design. Cochran lectured on both topics in his first quarter, and these lecture notes matured over the next ten years into his two well-known texts on these topics.
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Cox envisioned this program as half of the Institute of Statistics, the second part consisting of a Department of Mathematical Statistics at the University of North Carolina at Chapel Hill, headed by Haroict Hotelling. The Cochran's third child, Theresa, was born in North Carolina in 1946.
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ciata, we present some of his contributions to the theory ancT practice of sample surveys, follower! by brief mention of other areas of work.
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If the experimenter floes not clearly unclerstand the assumptions involved in the statistical manipulations, or the reasons for them, he loses confidence in the final results of the calculations." In several papers, Cochran gave substantial reviews intended to guide experimentation in specialized subject matters. For example, just before leaving the United Kingdom for the U.S.A., he presented a major review paper (1939a)
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on experimental design contains an instructive postscript on the rise of the use of experiments in the social sciences and the encouragement given to this movement by the Social Science Research Council. That postscript relates more generally to his stucly (1976)
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to begin applying probability theory (already available in astronomy) to interpret quantitative experiments and (2)
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After two years of discussions in depth of the principal experiments in surgery for duodenal ulcer, the group proclucect a comprehensive list of medical and statistical criteria for consideration in further experiments. Most of the criteria have value for design, anal
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Program arrangers often asked Cochran to provide a substantial general paper on the concluct of comparative studies intended to decicle causation. In discussing the advantages of matching subjects or materials as compared with the use of covariance adjustment in observational studies, he first notes!
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2361. In reviewing the ciangers of loading a stucly with so many research questions that it may fall of its own weight, he confessed, "But when clearing with an imaginative investigator ~ clo not finct it easy to determine at what point one should adamantly oppose all further questions, however ingenious ant!
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. Maxwell, in his introduction to the first organized text on counted data, Analysing Qualitative Data,4 said "l am indebted to .
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in any particular situation. (Amusingly enough, when Berkson gathered an enormous body of data to check whether radiation counts followoc!
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Yates hacI earlier clone an experimental demonstration of biases that resulted by allowing a judgmental selection of a "random sample" of plants. At a conference of the observers of the crop-weather scheme (for crop forecasting)
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In his work at Rothamstect, Cochran took advantage of the opportunities to be involved in practical studies in design and analysis of experiments and sample surveys. The samplesurvey experience inclucled, for example, evaluation of cropforecasting methods based jointly on sample-survey information on the crop and on weather data (193Sc)
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xs are the sample means, b is the usual estimate from the sample of the linear regression coefficient, and xp is the known population mean of the x characteristic. It was well known that this estimator is the minimum variance estimator of yp if the population regression of y on x is linear and if the conctitional variance of y given x is constant.
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Often variances are estimated by treating a systematic sample as equivalent to a stratified random sample. Some empirical studies have shown this to provi(le a reasonable approximation in many circumstances, but far from a satisfactory approximation in others.
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He obtained average variances for samples from the possible finite populations from such a superpopulation. For this class of populations he showed that: The stratified random sample is always at least as accurate on the average as the random sample and its relative efficiency is a monotone increasing function of the size of the sample.
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The problem of nonsampling errors in surveys is one that has received extensive attention, and in 1968 Cochran preparect a review paper and extenclect some of the earlier work that had been done in this area. He concluded, as clo others, that errors in measurement can sometimes seriously vitiate most stanciard statistical techniques anti at other times have only trivial effects clepencting on the size of the relevant response variances ant!
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In computing the estimated sampling error, Laplace assumed that the birth rate in each commune (and of course in all of France) was the consequence of sampling births and population at random with equal probability from the same urn, a finite superpopulation.
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the use of covariates in experiments and observational studies; (cI) the effect of errors of measurement on regression, analysis of variance, and the analysis of counted ciata; anti (e)
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Cochran limitecI his committee participation to the amount of work he could hancIle. He chaired the committee appointed by the American Statistical Association at the request of the National Academy of Sciences to review the Kinsey, Pomeroy, and Martin stucly of sexual behavior in the human male, work that resulted in a book (1954a)
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Bill received many honors. He was at various times presiclent of four major statistical organizations: the Institute of Mathematical Statistics in 1946, the American Statistical Association in 1953, the Biometric Society (which he helpecI found as a member of the organizing committee)
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L William Gemmell Cochran 1909-1980, A Personal Tribute.
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L11 1936 a. The statistical analysis of field counts of diseased plants.
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F361 b. Relative accuracy of systematic and stratified random samples for a certain class of populations.
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On a simple procedure of unequal probability sampling without replacement.
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F841 b. The planning of observational studies of human populations.
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Cochran.) 1983 Planning and Analysis of Observational Studies, ed.
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