Table 1 Grading criteria for review of carer intervention studies

   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-randomised 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