Table 2. Method of rating the certainty of the evidence for an outcome (2).

Step 1: starting grade according to study design

Randomised trials = high

Observational studies = low

Step 2: lower if

Risk of bias

Serious

Very serious

Inconsistency

Serious

Very serious

Indirectness

Serious

Very serious

Imprecision

Serious

Very serious

Publication bias

Serious

Very serious

Step 3: higher if

Large effect

Large

Very large

Dose response

Evidence of a gradient

All plausible confounding

Would reduce a demonstrated effect

Would suggest a spurious effect when results show no effect

Step 4: determine final grade for quality of evidence

High

Moderate

Low

Very low