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Table 2 National Health and Medical Research Council (NHMRC) levels of evidence

From: Chiropractic care for paediatric and adolescent Attention-Deficit/Hyperactivity Disorder: A systematic review

Level Intervention Studies
I Systematic review of level II studies
II Randomised controlled trial
III-I Pseudo-randomised controlled trial (i.e. alternate allocation or some other method)
III-2 Comparative study with concurrent controls:
  •Non-random, experimental trial
  •Cohort study
  •Case-control study
  •Interrupted time series with a control group
III-3 Comparative study without concurrent controls:
  •Historical control study
  •Two or more single arm study
  •Interrupted time series without a parallel control group
IV Case series with either post-test or pre-test/post-test outcomes
  1. NB. Adapted from NHMRC Levels of evidence [58]