Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
Prevention of pressure ulcers
Systematic review	1606 people 10 RCTs in this analysis	Rate of pressure ulcer formation with alternating-pressure surfaces with constant-low-pressure supports Absolute results not reported	RR 0.85 95% CI 0.64 to 1.13 P = 0.28 The meta-analysis pooled trials of several different types of surface and remains underpowered (the wide confidence intervals do not exclude a clinically important treatment effect). The review emphasised that many of the RCTs were small. It reported that further trials are needed to determine whether alternating-pressure devices and constant-low-pressure devices are associated with a clinically important difference in the risk of pressure ulceration		Not significant