Wednesday, January 22, 2020

Research Shorts: Rating the certainty in evidence in the absence of a single estimate of effect

Contributed by Madelin Siedler, 2019/2020 U.S. GRADE Network Research Fellow

When a pooled estimate from a meta-analysis of several studies is not present to guide the rating of evidence in these domains, how should one make a final determination of the certainty of evidence using GRADE? 

Evidence from a 30,000-foot view

In their 2017 paper published in Evidence-Based Medicine, Murad and colleagues describe methods for applying GRADE when bodies of evidence are either sparse or too disparate to pool. A systematic review, for instance, may only provide a narrative synthesis of the current evidence given these limitations. When a neat estimate of effect presented as part of a tidy forest plot is not available, it is necessary to use one’s best judgment to rate the domains by taking a broader view. In these cases, Murad et al. recommend the following approach:
  • Risk of Bias: Judge the risk of bias across all studies that include the outcome of interest.
  • Inconsistency: Consider the direction and size of the estimates of effect from each study. Generally, do they all tell the same story, or do they vary considerably?
  • Indirectness: Make an overall judgment about the amount of directness or indirectness of the body of evidence, given your specific question (always consider your population, intervention, outcome, and comparator[s] of interest). Generally, are the studies synthesized answering questions similar to yours? Or might the dissimilarities be enough to lower your trust in the estimate of effect as it pertains to your question?
  • Imprecision: Examine the total information size of all studies (number of events for binary outcomes, or number of participants for continuous outcomes) as well as each study’s reported confidence interval for this outcome. If there are fewer than 400 total events or participants, or if the confidence intervals from most studies - or the largest - include no effect, imprecision is likely present.
  • Publication bias: Suspect publication bias if there is a small number of only positive studies, or if data were reported in trial registries but never published.
As always, one may consider rating up the quality of evidence from an observational study if a large magnitude of effect, a dose-response gradient, or plausible residual confounding that would increase the certainty of effect are present in the majority of studies examined.

Murad MH, Mustafa RA, Schünemann HJ, Sultan S, Santesso N. Rating the certainty in evidence in the absence of a single estimate of effect. BMJ Evidence-Based Medicine. 2017 Jun 1;22(3):85-7.

Manuscript available here on publisher's site.

Monday, January 20, 2020

Research Shorts: Assessing the certainty of evidence in the importance of outcomes or values and preferences

Contributed by Madelin Siedler, 2019/2020 U.S. GRADE Network Research Fellow

The rating of outcomes in terms of their importance is a key aspect of GRADE guideline development. So is, of course, the rating of the certainty of evidence that will inform clinical decision-making. However, it is often difficult to rate the certainty of evidence of the importance of outcomes – assuming there is any evidence to draw from at all. In their July 2019 article published in the Journal of Clinical Epidemiology, Zhang and colleagues describe the ways to assess the certainty of a body of evidence used to determine the relative importance of outcomes.

The GRADE domains that present the most challenges when rating the certainty of evidence are inconsistency and imprecision. Assuming there is more than one study, assessment of inconsistency should include judging the amount of variance across studies’ reported importance of outcomes, exploring potential sources for this inconsistency (such as differences in populations or instruments used) and rating down when inconsistency is not explained by these. Imprecision should take into consideration the sample size first. In fact, in cases where there is no available quantitative synthesis, sample size may be the only consideration. In other cases, assuming information size meets a pre-defined threshold, the evidence may still be rated down if the confidence intervals of relative importance outcomes cross a pre-defined decision-making threshold.

Y. Zhang et al. (2019)/Journal of Clinical Epidemiology

The authors warn against attempts to rate the certainty of evidence in the variability of outcome importance – in other words, how much the perceived importance of any outcome varies from one individual to the next. If both inconsistency and imprecision are ruled out as potential sources of observed variance, then true variability may exist. In these cases, guideline panels should consider the formation of a conditional recommendation based on differences in values and preferences.

The article also provides guidance for assessing publication bias and rating up.

Zhang Y, Coello PA, Guyatt GH, Yepes-Nuñez JJ, Akl EA, Hazlewood G, Pardo-Hernandez H, Etxeandia-Ikobaltzeta I, Qaseem A, Williams Jr JW, Tugwell P. GRADE guidelines: 20. Assessing the certainty of evidence in the importance of outcomes or values and preferences—inconsistency, imprecision, and other domains. Journal of clinical epidemiology. 2019 Jul 1;111:83-93.

Manuscript available here on publisher's site.