Cobb 1997.

Methods	RCT with 40‐day follow‐up.
Participants	Recruitment in hospital wards and intensive care units. Participants > 18 y of age, ≤ 290 pounds, without pre‐existing pressure ulcer, an expected length of stay of 1‐2 weeks and considered at “high risk” on the basis of the Braden Scale. Patients allocated through the selection of a treatment card by an independent nurse. Some baseline imbalance observed with older participants; more participants with co‐morbidities in the KinAir group.
Interventions	1. Low loss air bed (KinAir Bed) (n = 62). 2. Static air mattress overlay (EHOB waffle) (n = 61).
Outcomes	Number of participants with incidence pressure ulcer (ICU participants assessed daily, ward patients assessed every 48 h): Grade 1 1. KinAir Bed 5% (3/62); 2. EHOB waffle 2% (1/61). Grade 2. 1. KinAir Bed 5% (3/62); 2. EHOB waffle 18% (11/61) Eschar 1. KinAir Bed 3% (2/62); 2. EHOB waffle 0/61.
Notes	No higher grades reported. No loss to follow‐up reported.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"Patients were placed into one of the study groups by random selection of a treatment card". Method of randomisation unclear.
Allocation concealment (selection bias)	Low risk	The use of an independent nurse picking a treatment card.
Blinding (performance bias and detection bias) Pressure ulcer incidence	Unclear risk	Not reported.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No numbers/reasons given for exclusions/attrition.
Selective reporting (reporting bias)	Low risk	All pre‐specified outcomes reported.
Free of other bias ‐ were groups similar at baseline regarding the most important prognostic indicators?	High risk	EHOB waffle group had more participants in younger age bracket; KinAir group had more with diabetes and cancer.
Free of other bias ‐ was the timing of the outcome assessment similar in all groups?	High risk	"Patients in the ICUs had skin assessments daily and those on the wards were assessed every 48 hours".