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.
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.