Appendix Table 1. Criteria for Grading the Internal Validity of Individual Studies

Randomized, controlled trials

• Clear definition of interventions.
• All important outcomes considered.
• Intention-to-treat analysis.
• Initial assembly of comparable groups.
  • Adequate randomization, including first concealment and whether potential confounders were distributed equally among groups.
  • Similar all-cause mortality among groups.
• Maintenance of comparable groups (includes attrition, crossovers, adherence, contamination).
• Important differential loss to follow-up or overall high loss to followup.
• Equal, reliable, and valid measurements (includes masking of outcome assessment).

Systematic Reviews

• Comprehensiveness of sources considered and search strategy used.
• Standard appraisal of included studies.
• Validity of conclusions.
• Recency and relevance (especially important).

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