Whitney 1984.

Study characteristics
Methods	Study objective: to provide data that will assist nurses in determining which mattress is the best choice for pressure sore prevention, and under which circumstances Study design: randomised controlled trial Study grouping: parallel group Duration of follow‐up: the average length of study 8.9 days in alternating pressure mattress; 7.6 in foam mattress Number of arms: 2 Single centre or multi‐sites: single centre Study start date and end date: not described Setting: medical‐surgical unit
Participants	Baseline characteristics Inclusion criteria: patients on 3 medical‐surgical units who were in bed for 20 out of 24 hours daily Exclusion criteria: not described Sex (M:F): not described Age (years): mean 63.2 (range 19 to 91) Baseline skin status: people with ulcers included (2 had serious decubiti on admission, 1 in each of the groups) Group difference: not reported Total number of participants: n = 51 Unit of analysis: individuals Unit of randomisation (per patient): individuals
Interventions	Intervention characteristics Alternating pressure mattress Description of interventions: an alternating pressure mattress consisting of 134 3‐inch diameter air cells with a 2.5‐inch lift, and micro air vents for air circulation. Adjacent air cells inflated and deflated alternately every 3 minutes. NPIAP S3I classification: powered, alternating pressure (active) air surface Co‐interventions: routine nursing care received including turning every 2 hours Number of participants randomised: n = 25 Number of participants analysed: n = 25 Foam mattress Description of interventions: a 4‐inch polyurethane convoluted foam pad NPIAP S3I classification: non‐powered, reactive foam surface; polyurethane convoluted foam Co‐interventions: routine nursing care received including turning every 2 hours Number of participants randomised: n = 26 Number of participants analysed: n = 26
Outcomes	Proportion of participants developing a new pressure ulcer Outcome type: binary Time points: not described Reporting: partially reported Measurement method (e.g. scale, self‐reporting): not described Definition (including ulcer stage): changes in skin condition; the definition of pressure ulcers not given Dropouts: not described Notes (e.g. other results reported): 20% of 25 with worse skin condition, 20% with better condition, and 60% with the same condition in alternating pressure mattress; 23.1% with worse skin condition, 19.2% with better condition, and 57.7% with the same condition in foam mattress Time to pressure ulcer incidence Reporting: not reported Support‐surface‐associated patient comfort Reporting: not reported All reported adverse events of using allocated support surfaces Reporting: not reported Health‐related quality of life (HRQOL) Reporting: not reported Cost‐effectiveness Reporting: not reported
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "26 were selected at random and placed in the foam mattress group, 25 in the AP mattress group" Comment: unclear risk of bias because it is unclear how random sequence was generated.
Allocation concealment (selection bias)	Unclear risk	Comment: no information provided.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Outcome group: primary outcome Quote: "... the investigators, who assessed the patient and placed him/her in one of the two mattress groups" Comment: high risk of bias because it is likely the investigators, i.e. key study personnel who operated the study, were not blinded.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Outcome group: primary outcome Quote: "In most cases patients were assessed by two investigators as a team, and occasionally by only one of the investigators" Quote: "The investigators who rated patient risk and evaluated skin condition knew the mattress assignment of each patient, making investigator bias possible" Comment: high risk of bias because non‐blinding of outcome assessment is clearly stated.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Comment: no information provided.
Selective reporting (reporting bias)	Unclear risk	Comment: no information provided.
Other bias	Unclear risk	Comment: no information provided.