We are very confident that the true association between the factor and the clinical effect lies close to the reported estimates.  Further research is very unlikely to change our confidence in the association.

• Several high-quality studies with consistent results
• In special cases: one large, high-quality multi-centre trial

We are moderately confident that the true association between the factor and the clinical effect lies close to the reported estimates, but there is a possibility that it is substantially different. Further research is likely to have an important impact on our confidence in the estimated association.

• One high-quality study
• Several studies with some limitations

Our confidence in the estimated association between the factor and the clinical effect is limited and the true association may not lie close to the reported estimates. Further research is very likely to have an important impact on our confidence in the estimate of any possible association.

• One or more studies with severe limitations

We have very little confidence in the estimates of an association between the factor and the clinical effect.  If an association exists, it is likely to be substantially different from the current estimates.

• Expert opinion
• No direct research evidence
• One or more studies with very severe limitations