Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
Prevention of pressure ulcers
Systematic review	409 people 2 RCTs in this analysis	Pressure ulcer development 13/221 (6%) with alternating-pressure surfaces 31/188 (16%) with standard foam mattress	RR 0.31 95% CI 0.17 to 0.58 P = 0.0002 The first RCT included in the analysis gave no indication of whether allocation concealment or blinded outcome assessment had been used, and in the second RCT, the denominators were numbers presented by the trial after withdrawals and attrition, and the analysis was not by intention to treat	Moderate effect size	alternating-pressure surfaces