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PubMed · 7950475

Statistical methods for clinical trials.

A Bailey·A Crook·D Machin
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Abstract

The object of this paper is to describe the essential features for the design and conduct of clinical trials. We include aspects of patient eligibility, random allocation to treatment including the principle of uncertainty, assessment of endpoints including those observed at different time points for each patient and trial size. Indications of appropriate methods of analysis are given, and the intention to treat principle is discussed. Some pointers to difficulties associated with data collection and management are included.

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BibTeXRIS

A Bailey, A Crook, D Machin. 1994. Statistical methods for clinical trials.. https://doi.org/10.1016/s0268-960x(05)80015-3

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The relation between treatment benefit and underlying risk in meta-analysis.

In meta-analyses of clinical trials comparing a treated group with a control group it has been common to ask whether the treatment benefit varies according to the underlying risk of the patients in the different trials, with the hope of defining which patients would benefit most and which least from medical interventions. The usual analysis used to investigate this issue, however, which uses the observed proportions of events in the control groups of the trials as a measure of the underlying risk, is flawed and produces seriously misleading results. This arises through a bias due to regression to the mean and will be particularly acute in meta-analyses which include some small trials or in which the variability in the true underlying risks across trials is small. Approaches which previously have been thought to be more appropriate are to substitute the average proportion of events in the control and treated groups as the measure of underlying risk or to plot the proportion of events in the treated group against that in the control group (L'Abbé plot). However, these are still subject to bias in most circumstances. Because of the potentially seriously flawed conclusions that can result from such analyses, they should be replaced either by statistically appropriate (but more complex) approaches or, preferably, by analyses which investigate the dependence of the treatment effect on measured baseline characteristics of the patients in each trial.

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