Whitney 1984.

Methods	RCT with 8‐day follow‐up. Method of allocation not reported; patients were "selected at random" for each group.
Participants	Patients on medical‐surgical units who were in bed for 20 h/day. Most patients had relatively little skin breakdown. Ages ranged from 19‐91 y; mean 63.2 y. Majority of patients were confused, lethargic, stuporous. Only 39% classed as mentally alert. Baseline data were not presented.
Interventions	1. Alternating‐pressure mattress (n = 25): consisted of 134 3‐inch diameter air cells. 3‐minute cycle. 2. Convoluted foam pad (Eggcrate) (n = 26). Patients in both groups were turned every 2 h.
Outcomes	Changes in skin condition did not differ significantly between patients using the alternating‐pressure air mattress and the foam mattress (better: 20% vs 19%; same: 60% vs 58%; worse 20% vs 23%).
Notes	4 patients died. Analysis by ITT. Alternating‐pressure mattress: pump maintenance was costly, patients objected to the movement. The alternating mattress was more easily cleaned and retained its original properties over several weeks compared to the foam, which compressed and flattened.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"26 were selected at random and placed in the foam mattress group, 25 in the AP mattress group...".
Allocation concealment (selection bias)	Low risk	"Upon recruitment, the data collector opened the next opaque envelope in sequence..." .
Blinding (performance bias and detection bias) Pressure ulcer incidence	Unclear risk	Not reported. Patients and nurses would not have been blinded.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No statement regarding drop‐outs/withdrawals, but there were 51 patients in the study and Table 3 (from study report) indicates that data for all of these were included (25 +26 = 51).
Selective reporting (reporting bias)	Low risk	The study was conducted to determine "...which mattress is the best choice for pressure sore prevention and under which circumstances".
Free of other bias ‐ were groups similar at baseline regarding the most important prognostic indicators?	Unclear risk	Not reported. Patient characteristics described for the group as a whole, not by mattress group.
Free of other bias ‐ was the timing of the outcome assessment similar in all groups?	Low risk	Description of outcome assessment seems to indicate all patients were treated the same, "Risk factors and skin assessment scores were recorded three times each week". It is noted that, "In most cases patients were assessed by two investigators as a team and occasionally by only one...", but that would not impact on timing of assessment.