Certainty index
Every outcome the Institute grades, organised by certainty level rather than by compound.
§1The four levels
A certainty rating describes confidence in an effect estimate for a stated population, comparator and outcome. It is not a recommendation, not an endorsement, and does not transfer to a different population, comparator or outcome.
Table 1. The four certainty levels and their meanings.
| Level | Graded outcomes | Meaning |
|---|---|---|
| High | 62 | The Institute is confident that the true effect lies close to the estimate. Further research is very unlikely to change confidence in the estimate. |
| Moderate | 114 | The true effect is likely to be close to the estimate, but there is a possibility that it is substantially different. Further research is likely to have an important impact on confidence in the estimate. |
| Low | 52 | Confidence in the effect estimate is limited. The true effect may be substantially different from the estimate. |
| Very low | 53 | The Institute has very little confidence in the effect estimate. The true effect is likely to be substantially different from the estimate. In this series a very low rating most often reflects an absence of controlled human evidence rather than conflicting evidence. |
§2How a rating is arrived at
Randomised evidence starts at high certainty. Each serious concern in one of five domains reduces the rating by one level and each very serious concern by two. Observational evidence starts at low and may be upgraded, rarely, where the effect is large, a dose–response gradient is present, or a plausible confounder would have reduced the observed effect.
Table 2. The five domains.
| Domain | What it assesses |
|---|---|
| Risk of bias | Limitations in the design and conduct of the contributing studies. |
| Inconsistency | Unexplained heterogeneity of results across contributing studies. |
| Indirectness | Differences between the population, intervention, comparator or outcome studied and those of the assessment question. |
| Imprecision | Width of the confidence interval relative to the decision threshold, and the number of events. |
| Publication bias | Risk that results were selectively reported or that unpublished studies exist. |