Table 2 Hierarchy of evidence
From: A systematic review of the efficacy and safety of fluoridation
Level | Intervention* | Aetiology/ harms† |
---|---|---|
I‡ | Systematic review of level II studies | Systematic review of level II studies |
II | RCT | Prospective cohort study |
III-1 | A pseudo-RCT (alternate allocation of some other method) | All or none¶ |
III-2 | A comparative study with concurrent controls Non-randomised experimental trial§ Cohort study Case–control study Interrupted time series with a control group | A retrospective cohort study |
III-3 | A comparative study without concurrent controls Historical control study Two or more single arm studies** | A case–control study |
IV | Case series with either pre-test/ post-test outcomes | A cross-sectional study |