Phillips 1999.

Study characteristics
Methods	Study objective: to compare the mattress overlay system with a second dynamic overlay Study design: randomised n‐of‐1 controlled trial, with a series design Study grouping: parallel group Duration of follow‐up: 12 weeks Number of arms: 2 Single centre or multi‐site: single centre Study start date and end date: not described Setting: community care
Participants	Baseline characteristics Inclusion criteria: those aged over 16 years old and did not have established pressure ulcers; in need of a pressure‐redistributing mattress; with a prognosis of remaining medically stable over 12 weeks; able to provide informed consent Exclusion criteria: not given Sex (M:F): overall 11:26 Age (years): overall median 87 (range 21 to 92) Baseline skin status: median Waterlow score 16 (range 13 to 26); without existing ulcers Group difference: no difference due to the use of n‐of‐1 trial design Total number of participants: n = 37 (the use of n‐of‐1 trial design means 37 trials are run) Unit of analysis: observations of each individual Unit of randomisation (per patient): order of treatment sequence
Interventions	Intervention characteristics Viaclin dynamic mattress overlay Description of interventions: Viaclin dynamic mattress overlay (formerly known as the Overture dynamic mattress overlay) consisting of 18 alternating pressure air cells ... manufactured in polyurethane (PU)‐coated nylon ... overlay cells inflate and deflate over a 12‐minute cycle by means of an electro‐pneumatic system NPIAP S3I classification: powered, alternating pressure (active) air surface Co‐interventions: not described Number of participants randomised: 37 participants Number of participants analysed: not given Alternative dynamic overlay Description of interventions: alternative dynamic overlay NPIAP S3I classification: powered, alternating pressure (active) air surface Co‐interventions: not described Number of participants randomised: 37 participants Number of participants analysed: not given
Outcomes	Proportion of participants developing a new pressure ulcer Outcome type: binary Time points: unclear Reporting: partially reported Measurement method (e.g. scale, self‐reporting): not given Definition (including ulcer stage): ulcer incidence Dropouts: unclear Notes (e.g. other results reported): 2 subjects developed an ulcer on the alternative overlay, 0 ulcers reported with the Viaclin mattress Time to pressure ulcer development Not reported Support‐surface‐associated patient comfort Reporting: partially reported Notes: 1 of 6 patients who failed on the alternative overlay was uncomfortable upon the overlay All reported adverse events using allocated support surfaces Not reported Health‐related quality of life (HRQOL) Not reported Cost‐effectiveness Not reported
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "On entry to the study, subjects were randomly allocated to either the Viaclin or an alternative dynamic overlay" Comment: unclear risk of bias because the sequence generation process is not described.
Allocation concealment (selection bias)	Unclear risk	Comment: no information provided.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Comment: no information provided.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: no information provided.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Comment: unclear risk of bias because data prior to cross‐over were not available. During the trials, 19 patients withdrew before the end of the trial.
Selective reporting (reporting bias)	High risk	Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes. We expected to see outcomes reported by randomised group per period, but this was not the case.
Other bias	High risk	Comment: high risk of bias because carry‐over effect is not considered in this study and correlation between repeated measurements on the same individual is not considered in data analysis. Data prior to cross‐over were not available.