Controlled clinical trials
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Control Clin Trials · Apr 1992
Biography Historical ArticleSir Austin Bradford Hill: an appreciation.
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Control Clin Trials · Feb 1992
ReviewImpact of random assignment on study outcome: an empirical examination.
Sixty research investigations published in the biomedical literature were analyzed to examine the effect of design attributes on outcome. All 60 studies included a controlled trial involving a pretest, a therapeutic intervention, and a posttest across at least two groups. Thirty of the trials used random assignment of participants to treatment or control conditions and 30 trials employed some nonrandom method of subject assignment. ⋯ Data analysis revealed that the trial results, as measured by effect size, did not vary across therapeutic trials using random assignment versus those using nonrandom allocation of subjects. The impact of design attributes in the interpretation of multiple clinical trials addressing a similar research question is examined. The argument is made that various design attributes frequently associated with methodological quality should be considered as important moderator variables and their influence on trial outcome should not be assumed a priori but rather examined empirically.
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Control Clin Trials · Dec 1989
Large trials with simple protocols: indications and contraindications.
The design of a clinical trial derives from its objective, which in its turn is dictated by the needs of clinical practice. Therefore, a common condition, a simple treatment, and a simple outcome measure are opportunities rather than design options. ⋯ If the treatment influences an intermediary outcome, which is assumed to have a causal role in the disease process that the treatment eventually seeks to influence, the effect on the intermediary outcome is of great importance--for clinical practice is very much centered around this outcome and the effects on intermediary outcomes may serve as an aid in explaining why there is an effect or why not. In conclusion, there are some research questions that may warrant large and simple trials, but many clinically very relevant research questions require a more complex trial design.
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This is the first of five articles on the properties of different randomization procedures used in clinical trials. This paper presents definitions and discussions of the statistical properties of randomization procedures as they relate to both the design of a clinical trial and the statistical analysis of trial results. The subsequent papers consider, respectively, the properties of simple (complete), permuted-block (i.e., blocked), and urn (adaptive biased-coin) randomization. ⋯ In an unmasked study, the potential for selection bias may be substantial with highly predictable sequences. Finally, the Efron model for accidental bias in the estimate of treatment effect in a linear model is described. This is important because the potential for accidental bias is equivalent to the potential for a covariate imbalance.(ABSTRACT TRUNCATED AT 400 WORDS)