Evidence level

Types of studies

1 a

Systematic Review (with homogeneity) of Randomized Controlled Trial;

1 b

Individual Randomized Controlled Trial (with narrow Confidence Interval);

1 c

All or none case-series;

2 a

Systematic Review (with homogeneity) of cohort studies;

2 b

Individual cohort study (including low quality Randomized Controlled Trial; e.g., <80% follow-up);

2 c

“Outcomes” Research; Ecological studies;

3 a

Systematic Review (with homogeneity) of case-control studies;

3 b

Individual Case-Control Study;

4

Case-series (and poor quality cohort and case-control studies);

5

Expert opinion without explicit critical appraisal, or based on physiology, bench research or “first principles”.