LOW RISK • Methods of blinding of outcome assessors described sufficiently and deemed adequate e.g. “The principal investigator saw the patients every day during their stay in the ward, and all complications were recorded by the same investigator. The randomisation code was not broken until all results were available and all patients had been followed up for 30 days after surgery and all complications classified.”

HIGH RISK Any one of the following: • Methods of blinding of outcome assessors described sufficiently but deemed inadequate • No blinding or incomplete blinding, and the outcome or outcome measurement is likely to be influenced by lack of blinding e.g. “This study was limited by small number of cases and the absence of blinding, placebo arm”

UNCLEAR RISK • Insufficient information to permit judgement of ‘Yes’ or ‘No’