Table 1 Critical appraisal questions for a cohort study

   1. Patient/population

   2. Number

   3. Setting

   4. Intervention

   5. Comparison/control

   6. Outcomes

   7. Inclusion criteria

   8. Exclusion criteria

Study validity

   1. Were there any conflicts of interest in the writing or funding of this study?

   2. Does the study have a clearly focused question?

   3. Is a cohort study the appropriate method to answer this question?

   4. Does the study have specified inclusion/exclusion criteria?

   5. If there were specified inclusion/exclusion criteria, were these appropriate?

   6. Other than the exposure under investigation, were the groups selected from similar populations?

   7. Aside from the exposure, were the groups treated the same?

   8. Was exposure measured in a standard, valid and reliable way?

   9. Were outcome assessors blind to the exposure?

   10. Were all outcomes measured in a standard, valid and reliable way?

   11. Were outcomes assessed objectively and independently?

   12. Is the paper free of selective outcome reporting?

   13. Were the outcomes measured appropriate?

   14. Was there sufficient duration of follow up?

   15. Was the study sufficiently powered to detect any differences between the groups?

   16. If statistical analysis was undertaken, was this appropriate?

   17. Were the groups similar at baseline with regards to key prognostic variables?

   18. What percentage of the individuals recruited into each arm of the study were lost to follow up?

   19. What percentages of the individuals were not included in the analysis?

Other

   1. What is the overall risk of bias?

Results

Authors' conclusions

Our comments