Table 1 Grade Criteria

Grade I (Strong evidence)

 RCTs or review of RCTS

  IA Calculation of sample size and accurate standard definition of appropriate outcome variables

  IB Accurate and standard definition of appropriate outcome variables

  IC Neither of the above

Grade II (Fairly strong evidence)

 Prospective study with a comparison group (non-randomized controlled trial, good observational study or retrospective study that controls effectively for confounding variables)

  IIA Calculation of sample size and accurate, standard definition of appropriate outcome variables and adjustment for the effects of important confounding variables

  IIB One or more of the above

Grade III (Weaker evidence)

 Retrospective or observational studies

  IIIA Comparison group, calculation of sample size, accurate and standard definition of appropriate outcome variables

  IIIB Two or more of the above

  IIIC None of these

Grade IV (Weak evidence)

 Cross-sectional study, Delphi exercise, consensus of experts