Dealing with substantial heterogeneity in Cochrane reviews. Cross-sectional study

<p>Abstract</p> <p>Background</p> <p>Dealing with heterogeneity in meta-analyses is often tricky, and there is only limited advice for authors on what to do. We investigated how authors addressed different degrees of heterogeneity, in particular whether they used a fixed effect model, which assumes that all the included studies are estimating the same true effect, or a random effects model where this is not assumed.</p> <p>Methods</p> <p>We sampled randomly 60 Cochrane reviews from 2008, which presented a result in its first meta-analysis with substantial heterogeneity (I²greater than 50%, i.e. more than 50% of the variation is due to heterogeneity rather than chance). We extracted information on choice of statistical model, how the authors had handled the heterogeneity, and assessed the methodological quality of the reviews in relation to this.</p> <p>Results</p> <p>The distribution of heterogeneity was rather uniform in the whole I²interval, 50-100%. A fixed effect model was used in 33 reviews (55%), but there was no correlation between I²and choice of model (P = 0.79). We considered that 20 reviews (33%), 16 of which had used a fixed effect model, had major problems. The most common problems were: use of a fixed effect model and lack of rationale for choice of that model, lack of comment on even severe heterogeneity and of reservations and explanations of its likely causes. The problematic reviews had significantly fewer included trials than other reviews (4.3 vs. 8.0, P = 0.024). The problems became less pronounced with time, as those reviews that were most recently updated more often used a random effects model.</p> <p>Conclusion</p> <p>One-third of Cochrane reviews with substantial heterogeneity had major problems in relation to their handling of heterogeneity. More attention is needed to this issue, as the problems we identified can be essential for the conclusions of the reviews.</p

Improving GRADE evidence tables part 2: a systematic survey of explanatory notes shows more guidance is needed

Objectives: The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) working group has developed GRADE evidence profiles (EP) and summary of findings (SoF) tables to present evidence summaries in systematic reviews, clinical guidelines, and health technology assessments. Explanatory notes are used to explain choices and judgments in these summaries, for example, on rating of the quality of evidence. Study Design and Setting: A systematic survey of the explanations in SoF tables in 132 randomly selected Cochrane Intervention reviews and in EPs of 10 guidelines. We analyzed the content of 1,291 explanations using a predefined list of criteria. Results: Most explanations were used to describe or communicate results and to explain downgrading of the quality of evidence, in particular for risk of bias and imprecision. Addressing the source of baseline risk (observational data or control group risk) was often missing. For judgments about downgrading the quality of evidence, the percentage of informative explanations ranged between 41% (imprecision) and 79% (indirectness). Conclusion: We found that by and large explanations were informative but detected several areas for improvement (e.g., source of baseline risk and judgments on imprecision). Guidance about explanatory footnotes and comments will be provided in the last article in this series. (C) 2016 Elsevier Inc. All rights reservedCochrane Collaboration's Methods Innovation Fund McMaster GRADE Cente

Improving GRADE evidence tables part 2 : A systematic survey of explanatory notes shows more guidance is needed

Objectives: The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) working group has developed GRADE evidence profiles (EP) and summary of findings (SoF) tables to present evidence summaries in systematic reviews, clinical guidelines, and health technology assessments. Explanatory notes are used to explain choices and judgments in these summaries, for example, on rating of the quality of evidence. Study Design and Setting: A systematic survey of the explanations in SoF tables in 132 randomly selected Cochrane Intervention reviews and in EPs of 10 guidelines. We analyzed the content of 1,291 explanations using a predefined list of criteria. Results: Most explanations were used to describe or communicate results and to explain downgrading of the quality of evidence, in particular for risk of bias and imprecision. Addressing the source of baseline risk (observational data or control group risk) was often missing. For judgments about downgrading the quality of evidence, the percentage of informative explanations ranged between 41% (imprecision) and 79% (indirectness). Conclusion: We found that by and large explanations were informative but detected several areas for improvement (e.g., source of baseline risk and judgments on imprecision). Guidance about explanatory footnotes and comments will be provided in the last article in this series