Clinical trial bias research update

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Recommended reading from Anne Taylor-Vaisey: I think this article from the March 2006 issue of the American Journal of Epidemiology is of interest, particularly in light of the NEJM's recent "reaffirmation of concern" re the VIGOR (VIOXX) study.


Gluud LL. Bias in clinical intervention research. Am J Epidemiol 2006;163:493-501.


Abstract: Research on bias in clinical trials may help identify some of the reasons why investigators sometimes reach the wrong conclusions about intervention effects. Several quality components for the assessment of bias control have been suggested, but although they seem intrinsically valid, empirical evidence is needed to evaluate their effects on the extent and direction of bias. This narrative review summarizes the findings of methodological studies on the influence of bias in clinical trials. A number of methodological studies suggest that lack of adequate randomization in published trial reports may be associated with more positive estimates of intervention effects. The influence of double-blinding and follow-up is less clear. Several studies have found a significant association between funding sources and pro-industry conclusions. However, the methodological studies also show that bias is difficult to detect and appraise. The extent of bias in individual trials is unpredictable. A-priori exclusion of trials with certain characteristics is not recommended. Appraising bias control in individual trials is necessary to avoid making incorrect conclusions about intervention effects.

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Excerpt re Competing Interests:


The reason for the association between funding and pro-industry conclusions is not clear. Potential explanations include violation of the uncertainty principle, publication bias, and biased interpretation of trial results. The uncertainty principle means that patients should be enrolled in a trial only if there is substantial uncertainty about which of the treatments in the trial is most appropriate for the patient. Trials may be considered unethical if patients allocated to the control group are not offered a known effective intervention. A violation of the uncertainty principle may be related to selective sponsoring of trials with known beneficial effects.

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