Leaper 1977.

Methods	RCT Methods to control for contributory patient factors: none
Participants	Age: not stated Gender: Group 1 female 54.3% Group 2 female 53% Group 3 female 46.7% Types of incisions: Group 1 paramedian 11.2%, midline 56.9%, transverse 31.9% Group 2 paramedian 10.7%, midline 53.7%, transverse 35.5% Group 3 paramedian 10%, midline 54.1%, transverse 35.8% Types of surgery: Group 1 colorectal 26.7%, biliary 20.7%, gastric 28.4%, miscellaneous 24.1% Group 2 colorectal 26.4%, biliary 28.9%, gastric 22.3%, miscellaneous 22.3% Group 3 colorectal 27.5%, biliary 25.8%, gastric 34.2%, miscellaneous 12.5% Contamination classification of included participants: Preoperative antibiotic use: Prognostic patient factors: Malignancy: Group 1 25.8%, Group 2 34.7%, Group 3 36.7% COPD: Group 1 44%, Group 2 52%, Group 3 42% Hypoproteinaemia: Group 1 11%, Group 2 10%, Group 3 5% Inclusion criteria: major laparotomies Exclusion criteria: appendectomy through muscle‐splitting incision, lumbar sympathectomy, renal bladder and prostatic surgery, incisions through previous scars
Interventions	Comparisons reported: Group 1: Sutures: nylon (monofilament, non‐absorbable) Suture technique: continuous Closure method: layered (peritoneum and posterior sheath closed with chromic catgut, anterior sheath by nylon) Group 2: Sutures: PGA (multifilament, fast absorbable) Suture technique: interrupted (Smead Jones) Closure method: mass closure Group 3: Sutures: steel (monofilament, non‐absorbable) Suture technique: interrupted (Smead Jones) Closure method: mass closure Characteristics of surgeons: Consultant: Group 1 25.8%, Group 2 28.9%, Group 3 30%
Outcomes	Hernia: bulge noticeable by patient and assessor upon standing Follow‐up duration: 6 months Wound infection: primary sepsis is discharge of pus from a previously dry wound, secondary sepsis is acquisition of infection by a discharging wound. Major sepsis involves the deep layers of the wound and is accompanied by constitutional symptoms Dehiscence: separation of deep layers, heralded by discharge of ascites Sinus or fistula: not defined
Notes	Hernia data excluded from analysis due to inadequate follow‐up duration Group 2 compared with group 3 for 'absorbable versus non‐absorbable' and 'monofilament versus multifilament' as they share a common closure technique and method Group 2 and 3 analysed together as 'interrupted', 'mass'
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomisation was by "means of instructions in a sealed envelope"
Allocation concealment (selection bias)	Low risk	Sealed envelope
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Not described
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants accounted for and analysed
Selective reporting (reporting bias)	Low risk	There was no evidence of selective reporting
Other bias	High risk	Surgeons refused randomisation in 17 cases