Evaluation of risk of bias assessment of trials in systematic reviews of oral health interventions, 1991-2014: A methodology study

Abstract

Background: The authors aimed to describe how often and by what means investigators assessed the risk of bias of clinical trials in systematic reviews of oral health interventions and to identify factors associated with risk of bias assessments.

Methods: The authors selected therapeutic oral health systematic reviews published from 1991 through 2014. They extracted data related to the tools used for risk of bias assessment of primary studies and data related to other review characteristics. They descriptively analyzed the data and used multivariate logistic regression.

Results: The authors identified 1,114 oral health systematic reviews (130 Cochrane reviews and 984 non-Cochrane reviews). The investigators of the primary studies assessed risk of bias in 61.4% of the reviews, and the risk of bias assessments occurred more often in Cochrane reviews than in non-Cochrane reviews (100% versus 56.3%; P < .001) and in reviews published after the dissemination of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement (odds ratio [OR], 1.55; 95% confidence interval [CI], 1.17-2.06). Compared with the investigators of reviews of public oral health interventions, investigators of reviews of oral surgery were less likely to assess risk of bias (OR, 0.41; 95% CI, 0.25-0.67). Furthermore, the investigators of systematic reviews published in dental journals were less likely to assess risk of bias of individual trials (OR, 0.28; 95% CI, 0.19-0.41) compared with the investigators of reviews published in nondental journals.

Conclusions: The investigators of primary studies did not undertake risk of bias assessment in a considerable portion of non-Cochrane oral health systematic reviews. The investigators of reviews published in dental journals were less likely to assess risk of bias than the investigators of reviews published in nondental journals. The results of this study provide evidence of the need for improving the conduct and reporting of oral health systematic reviews with respect to risk of bias assessment.

Practical implications: Clinicians should determine to what extent the findings of a systematic review are valid on the basis of whether the investigators assessed and considered risk of bias during the interpretation of findings.

Keywords: Dentistry; bias; meta-analysis; randomized controlled trial; study quality; systematic review.