Overall grades of evidence
|
| High |
Further research is very unlikely to change our confidence in the estimate of effect. |
| Moderate |
Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. |
| Low |
Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. |
| Very Low |
Any estimate of effect is very uncertain. |
Above based on criteria for assigning grade of evidence
|
| Types of evidence |
|
| High |
Randomized trial |
| Low |
Observational study (cohort studies, case-control studies, interrupted time series analyses, controlled before and after studies |
| Very low |
Any other evidence |
Decrease grade if:
|
• Serious (–1) or very serious (–2) limitation to study quality
|
• Important inconsistency (–1)
|
• Some (–1) or major (–2) uncertainty about directness
|
• Imprecise or sparse data (–1)
|
• High probability of reporting bias (–1)
|
Increase grade if:
|
• Strong evidence of association–significant relative risk of >2 based on consistent evidence from two or more observational studies with no plausible confounders (+1)
|
• Very strong evidence of association–significant relative risk of >5 based on direct evidence with no major threats to validity (+2)
|
• Evidence of a dose-response gradient
|
• All plausible confounders would have reduced the effect (+1)
|
| Recommendation: |
‘Do it’ or ‘Don’t do it’–indicating a judgment that most well-informed people would make |
| Suggestion: |
‘Probably do it’ or ‘Probably don’t do it’–indicating a judgment that a majority of well-informed people would make but a substantial minority would not |