Table 2.

Levels of evidence for therapeutic studies

Level of evidence	Investigating the results of treatment (therapeutic studies)
1	High-quality randomized trial with a statistically significant difference or no statistically significant difference but narrow confidence intervals; systematic review of level 1 RCTs (the study results were homogenous)
2	Lesser quality RCT (e.g., <80% follow-up, no blinding, or improper randomization), prospective comparative study, systematic review of level 2 or level 1 studies with inconsistent results
3	Case control study, retrospective comparative study, and systematic review of level 3 studies
4	Case series
5	Recommendations