ROBERT S. HOLZMAN, M.D.
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To the editor: It has become a common practice, in the Annals and elsewhere, to describe the duration of a clinical study in patient-years (the sum of the number of years each patient was followed). Thus, if 3 patients were followed for 6 years and 12 for 1 year, we would have 30 patient-years of experience.
The inflationary nature of this procedure is obvious in the example. More important, no adequate estimate of the usual duration of follow-up and its variability can be obtained from the number of patient-years. Dividing by the number of patients does give the mean duration,
ROBERT S. HOLZMAN. Proper Statistics for Clinical Studies. Ann Intern Med. 1971;75:649. doi: 10.7326/0003-4819-75-4-649_2
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Published: Ann Intern Med. 1971;75(4):649.
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