Table 2.

Definitions used for the grades of evidence

Grade I: Randomised controlled trial (RCT)
IA Calculation of sample size and accurate, standard definition of outcome variables
IB Accurate and standard definition of outcome variables.
IC Neither of the above
Grade II: Prospective study with a comparison group (non randomised controlled trial, observational study) or retrospective study which controls for confounding variables
IIA Calculation of sample sizea and accurate, standard definition of outcome variables and adjustments for the effects of important confounding variables
IIB One or more of the above
IIC Neither of the above
Grade III Retrospective or observational or cross-sectional studies
IIIA Comparison group, calculation of sample size and accurate, standard definition of outcome variables
IIIB One or more of the above
IIIC Neither of the above.

^aIf sample size above 1000 or more we considered this criteria to have been reached