Nherera 2017.

Methods	Study design: randomised controlled trial (economic evaluation based on the Karlakki 2016 RCT) Study grouping: parallel Ethics and informed consent: yes Follow‐up period: 6 weeks Sample size estimate: pilot study ITT analysis: yes number randomised: 220 number analysed: 209 Funding: study funded through a grant from Smith & Nephew, UK, to cover the cost of NPWT dressings and data collection costs. 2 investigators declared they had funding and consultancy fees from Smith & Nephew. Pre‐registration: no
Participants	Location: Oswestry, UK Intervention group: n = 110control group: n = 110 Mean age (SD): intervention group = 69 (9.0)control group = 69.2 (9.0) Inclusion criteria: patients undergoing THAs or TKAs (for any indication) with 3 consultant surgeons (SLK, NMG, and RDB – authors of this study) Exclusion criteria: patients who had known allergies to dressing, were undergoing revision joint surgery, were unwilling to attend additional clinics, and those on warfarin were excluded.
Interventions	Aim/s: to evaluate the cost‐effectiveness of incisional NPWT dressing Group 1 (NPWT) intervention: PICO dressing applied over the primarily closed incision by the surgeon in the operating room. Dressing was left on for 4 days, or longer if drainage continued, unless soiled or dislodged. Group 2 (control) intervention: Comfeel dressing applied over the primarily closed incision by the surgeon in the operating room. Dressing was left on for 4 days, or longer if drainage continued, unless soiled or dislodged. Study date/s: July 2012 to April 2014
Outcomes	cost‐effectiveness
Notes	The first 2 authors are employed by Smith & Nephew, UK (manufacturers of the intervention product). Quality rating using the CHEERS checklist was 85.4%.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "the randomisation was performed using sealed opaque envelopes with a block size of 20 shuffled envelopes" Comment: unclear how the random sequence was generated
Allocation concealment (selection bias)	High risk	Quote: "the randomisation was performed using sealed opaque envelopes with a block size of 20 shuffled envelopes" Comment: surgeons knew at the start of the surgery to which group participants had been randomised.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Evidence for participants: not possible Comment: unlikely to affect outcomes Evidence for personnel: not possible Comment: unlikely to affect outcomes
Blinding of outcome assessment (detection bias) All outcomes	High risk	Outcome assessors were aware of group allocation.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	7.3% in intervention group and 2.7% in control group based on a PP analysis Comment: more intervention participants were excluded from the analysis (8 intervention vs 3 control).
Selective reporting (reporting bias)	Low risk	Stated outcomes were reported.
Other bias	Low risk	No other biases detected.