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.
The article also provides guidance for assessing publication bias and rating up.
Manuscript available here on publisher's site.
