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‐site: unspecified Study start date and end date: not described Setting: 3 medical‐surgical units.
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 has serious decubiti on admission, 1 in each of the groups) Group difference: 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 three‐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 development Reporting: not reported Support‐surface‐associated patient comfort Reporting: not reported All reported adverse events 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 the 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 performed this study.
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.