Evidence-Based Medicine
Copyright ©The Author(s) 2016.
World J Gastroenterol. Jul 21, 2016; 22(27): 6296-6317
Published online Jul 21, 2016. doi: 10.3748/wjg.v22.i27.6296
Table 2 Oxford Centre for Evidence-Based Medicine evidence levels of evidence scale
LevelStudy questions on therapy/prevention, etiology/harm
1aSystematic review (with homogeneity of RCTs)
1bIndividual RCT (with narrow confidence intervals)
1cAll or none studies
2aSystematic review (with homogeneity) of cohort studies
2bIndividual cohort study (including low quality RCT, e.g., < 80% follow-up)
2cOutcomes research: ecological studies
3aSystematic review (with homogeneity) of case control studies)
3bIndividual case control study
4Case-series (and poor quality cohort an case control studies ++)
5Expert opinion without explicit critical appraisal or based on physiology, bench research or first principles