Table 1.
Grading the overall certainty of evidence according to methodological quality, outcome-specific certainty of evidence, biological plausibility and consistency of results, and definition of the overall certainty of evidence in a modified form according to the GRADE approach [23, 26]
| Overall certainty of evidence | Underlying criteria | Definition/explanation |
|---|---|---|
| Convincing |
• At least one SR with or without MA of prospective studies available • If more than one SR with or without MA are available: all overall results must be consistent.1 • In case of a positive or negative association, biological plausibility is given • All included SRs with or without MA must reach at least a “moderate” outcome-specific certainty of evidence2; in addition all included SRs must reach at least a methodological quality3 of “moderate” |
There is high level of confidence that the true effect lies close to that of the estimate(s) of the effect |
| Probable |
• At least one SR with or without MA of prospective studies available • If more than one SR with or without MA are available, the majority of overall results must be consistent.1 • In case of a positive or negative association, biological plausibility is given • The majority4 of included SRs with or without MA must have reached at least a “moderate” certainty of evidence2; in addition all included SRs must reach at least a methodological quality3 of “moderate” |
There is moderate confidence in the effect estimate(s): The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different |
| Possible |
• At least one SR with or without MA of prospective studies available • If more than one SR with or without MA are available, the majority of overall results must be consistent.1 • In case of a positive or negative association, biological plausibility is given • The majority4 of included SRs with or without MA must reach at least a “low” certainty of evidence2; in addition the majority4 of all included SRs must reach at least a methodological quality3 of “moderate” |
Confidence in the effect estimate(s) is limited: The true effect may be substantially different from the estimate of the effect |
| Insufficient |
• No SR is available OR • The majority4 of included SRs with or without MA reach a “very low” certainty of evidence2; in addition the majority of all included SRs reach a methodological quality3 of “low” |
There is very little confidence in the effect estimate (s): The true effect is likely to be substantially different from the estimate of effect |
MA meta-analysis, SR systematic review
1Consistent = overall results of the SR have to be consistently either risk reducing or risk elevating or consistently showing no risk association
2Outcome-specific certainty of evidence refers to the NutriGrade rating
3Methodological quality refers the AMSTAR 2 rating; SRs graded as “critically low” by AMSTAR 2 are not considered
4Majority: > 50% of the included SRs