Statistics in medicine
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Statistics in medicine · Aug 1990
Historical ArticleSome historical and methodological developments in early clinical trials at the National Institutes of Health.
This paper reviews five randomized clinical trials with unusual design or analysis features from institutes other than the National Cancer Institute or the National Heart, Lung and Blood Institute. These are: a Cooperative Study of Retrolental Fibroplasia sponsored by the National Institute of Neurological Diseases and Blindness; the Diabetic Retinopathy Study sponsored by the National Eye Institute; the University Group Diabetes Program sponsored by the National Institute of Arthritis and Metabolic Diseases; a Clinical Trial of the Extracranial to Intracranial Arterial Anastomosis (EC/IC bypass) by the National Institute of Neurological and Communicative Disorders and Stroke; and the Clinical Trial of Hereditary Angioedema by the National Institute of Allergy and Infectious Diseases.
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Randomized consent designs were introduced to make it easier for physicians to enter patients in randomized clinical trials. Physician reluctance to participate in randomized clinical trials is often a reflection that the physician-patient relationship could be compromised if the physician makes known to the patient his/her inability to select a preferred therapy. Clinical trials having a no-treatment control or placebo amplify this concern. This paper reviews the main ideas of randomized consent designs (single and double) and the statistical model underlying the analysis, and presents some recent experiences.
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Statistics in medicine · Jan 1990
Randomized Controlled Trial Multicenter Study Clinical Trial Historical ArticlePolio trial: an early efficient clinical trial.
The Salk Vaccine Field Trial was a randomized, placebo-controlled trial designed to test the efficacy of the Salk killed virus vaccine. Although the trial was not without some problems, both in design and analysis, none was important enough to raise serious questions about the results. ⋯ The trial owes its success in a large part to substantial public involvement. In designing future, large-scale, simple trials, we may still be able to benefit from the lessons of the Polio Vaccine Trial.
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Statistics in medicine · Nov 1988
Explanatory and pragmatic estimates of the treatment effect when deviations from allocated treatment occur.
In a randomized clinical trial comparing two treatments it can happen that certain patients receive the treatment other than that determined by random allocation. Significance testing is usually performed by 'intention to treat', that is, comparison of groups as determined by random allocation. ⋯ Thus two distinct estimates are obtained; in many instances both are valid, but have distinct interpretations. Correspondingly, in planning sample size requirements when deviations from allocated treatment can be anticipated, the target treatment difference may be understood in either an explanatory or a pragmatic sense; for the sample size assessment method it is necessary to take this distinction into account.
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Statistics in medicine · Sep 1988
Exposure-response relationship for a dichotomized response when the continuous underlying variable is not measured.
Radiological assessment of pneumoconiosis is an example of a dichotomized variable, namely one that is analysed as a binary response but in fact has an underlying continuum, which in this case is not measurable. Estimates of exposure-response relationships vary greatly for different observers of a dichotomized response variable because of random error of measurement and differences in the threshold implicitly chosen by each observer for categorizing cases. We present a method of using the biserial correlation coefficient and normal distribution theory to estimate exposure-response relationships at any required threshold for each observer. Exposure-response relationships can also be corrected for random observational error using the reliability coefficient, calculated as the tetrachoric correlation between repeat observations by readers.