Kemp 1993.

Study characteristics
Methods	Study objective: to compare the effectiveness of 2 types of overlays intended to prevent pressure ulcers: a convoluted foam mattress overlay and a solid foam mattress overlay Study design: randomised controlled trial Study grouping: parallel group Duration of follow‐up: 1 month Number of arms: 2 Single centre or multi‐sites: multi‐sites Study start date and end date: March 1989 and November 1989 Setting: a tertiary‐care medical centre (acute setting) and a long‐term care facility
Participants	Baseline characteristics Inclusion criteria: patients without pressure ulcers who are at least 65 years old and had a Braden score of 16 or less (at risk) Exclusion criteria: not described Sex (M:F): 26:58 overall; 14:31 in convoluted foam; 12:27 in solid foam Age (years): overall mean 81 (SD 8); 79.31 (7.54) in convoluted foam and 82.64 (8.60) in solid foam Baseline skin status: mean Braden score 14.00 (SD 1.73) in convoluted foam; 13.85 (1.71) in solid foam Group difference: no difference Total number of participants: 84 Unit of analysis: individuals Unit of randomisation (per patient): individuals
Interventions	Intervention characteristics Convoluted foam mattress overlay Description of interventions: either a 3‐inch overlay with a density of 1.42 Ib per cubic foot or a 4‐inch overlay (density unknown) NPIAP S3I classification: non‐powered, reactive foam surface; foam with a density of 22.7 kg/m3 Co‐interventions: not described Number of participants randomised: n = 45 Number of participants analysed: n = 45 Solid foam mattress overlay Description of interventions: a 4‐inch solid, sculptured overlay with a density of 1.33 lb per cubic foot NPIAP S3I classification: non‐powered reactive foam surface; foam with a density of 21.3 kg/m3 Co‐interventions: not described Number of participants randomised: n = 39 Number of participants analysed: n = 39
Outcomes	Proportion of participants developing a new pressure ulcer Outcome type: binary Time points: 1 month Reporting: fully reported Measurement method (e.g. scale, self‐reporting): assessed by research nurses using NPIAP 1989 system Definition (including ulcer stage): no. of patients with pressure ulcers of any grade Dropouts: no missing data Notes (e.g. other results reported): 21 of 45 in convoluted foam; 12 of 39 in solid foam. All grade 1 and 2 ulcers; no grade 3 or grade 4 ulcers Time to pressure ulcer incidence Reporting: partially reported Notes (e.g. other results reported): hazard ratio for convoluted foam vs solid foam of exp(0.906) = 2.47 and P = 0.018 in a Cox regression model adjusted for mobility score (solid foam as reference); 'The positive coefficient (0.906) for overlay type indicated that the risk of developing a pressure ulcer was greater for patients nursed on convoluted foam than for patients nursed on solid foam when the averaged mobility score was also taken into account'; estimated HR 2.47 (95% CI 1.25 to 4.90) (or lnHR 0.906, se 0.35). Note that the averaged mobility scores were adjusted for by the study authors rather than scores at baseline. 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)	Low risk	Quote: "At each clinical site, a random number table was used to assign study patients to ..." Comment: low risk of bias because of the use of a random number table.
Allocation concealment (selection bias)	Unclear risk	Comment: no information provided.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Outcome group: primary outcome Comment: no information provided.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Outcome group: primary outcome Quote: "The research nurses recorded their skin assessments on a form developed for this study" Comment: unclear risk of bias because no information on blinding provided.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: no missing data.
Selective reporting (reporting bias)	Low risk	Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre‐specified.
Other bias	Low risk	Comment: the study appears to be free of other sources of bias.