Bias and small-study effects influence treatment effect estimates: a meta-epidemiological study in oral medicine (original) (raw)
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BMJ open, 2014
It is fundamental that randomised controlled trials (RCTs) are properly conducted in order to reach well-supported conclusions. However, there is emerging evidence that RCTs are subject to biases which can overestimate or underestimate the true treatment effect, due to flaws in the study design characteristics of such trials. The extent to which this holds true in oral health RCTs, which have some unique design characteristics compared to RCTs in other health fields, is unclear. As such, we aim to examine the empirical evidence quantifying the extent of bias associated with methodological and non-methodological characteristics in oral health RCTs. We plan to perform a meta-epidemiological study, where a sample size of 60 meta-analyses (MAs) including approximately 600 RCTs will be selected. The MAs will be randomly obtained from the Oral Health Database of Systematic Reviews using a random number table; and will be considered for inclusion if they include a minimum of five RCTs, and...
BMJ, 2008
Objective To examine whether the association of inadequate or unclear allocation concealment and lack of blinding with biased estimates of intervention effects varies with the nature of the intervention or outcome. Design Combined analysis of data from three metaepidemiological studies based on collections of metaanalyses. Data sources 146 meta-analyses including 1346 trials examining a wide range of interventions and outcomes. Main outcome measures Ratios of odds ratios quantifying the degree of bias associated with inadequate or unclear allocation concealment, and lack of blinding, for trials with different types of intervention and outcome. A ratio of odds ratios <1 implies that inadequately concealed or nonblinded trials exaggerate intervention effect estimates. Results In trials with subjective outcomes effect estimates were exaggerated when there was inadequate or unclear allocation concealment (ratio of odds ratios 0.69 (95% CI 0.59 to 0.82)) or lack of blinding (0.75 (0.61 to 0.93)). In contrast, there was little evidence of bias in trials with objective outcomes: ratios of odds ratios 0.91 (0.80 to 1.03) for inadequate or unclear allocation concealment and 1.01 (0.92 to 1.10) for lack of blinding. There was little evidence for a difference between trials of drug and nondrug interventions. Except for trials with all cause mortality as the outcome, the magnitude of bias varied between meta-analyses. Conclusions The average bias associated with defects in the conduct of randomised trials varies with the type of outcome. Systematic reviewers should routinely assess the risk of bias in the results of trials, and should report meta-analyses restricted to trials at low risk of bias either as the primary analysis or in conjunction with less restrictive analyses.
The Journal of the American Dental Association, 2016
ystematic reviews and meta-analyses of randomized controlled clinical trials are considered to be a criterion standard form of evidence to indicate the efficacy and effectiveness of therapeutic interventions in health sciences. 1 The authors of systematic reviews use a comprehensive search strategy to identify all potentially relevant trials, predefine eligibility criteria to minimize the impact of bias in study selection, and use reproducible methods to assess the risk of bias found in individual trials and to consider that risk when synthesizing their results. 2 As with any research design, the value of a systematic review depends on how well its authors conduct and report the results. The endorsement by journal editors, reviewers, and authors of reporting guidelines such as the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement 3 has resulted in increases in both the reporting and the methodological quality of published reviews. 4 In the area of oral health, approximately 50 dentistry-related trials are published per month, and this number increases every year. 5 Similarly, the number of systematic reviews published in oral health and within dental
Journal of dental research, 2017
Emerging evidence suggests that design flaws of randomized controlled trials can result in over- or underestimation of the treatment effect size (ES). The objective of this study was to examine associations between treatment ES estimates and adequacy of sequence generation, allocation concealment, and baseline comparability among a sample of oral health randomized controlled trials. For our analysis, we selected all meta-analyses that included a minimum of 5 oral health randomized controlled trials and used continuous outcomes. We extracted data, in duplicate, related to items of selection bias (sequence generation, allocation concealment, and baseline comparability) in the Cochrane Risk of Bias tool. Using a 2-level meta-meta-analytic approach with a random effects model to allow for intra- and inter-meta-analysis heterogeneity, we quantified the impact of selection bias on the magnitude of ES estimates. We identified 64 meta-analyses, including 540 randomized controlled trials ana...