Adloff 1987.

Methods	Randomised clinical trial Generation of the allocation sequence: unclear. Allocation concealment: adequate. Sealed box. Blinding: none (inadequate). Follow‐up: adequate. Intention‐to‐treat analysis: no. Sample size calculation: no.
Participants	Country: France. Number randomised: 200. Mean age: 49.9 years. Females: 164. Inclusion criteria: Elective cholecystectomy. Exclusion criteria: CBD exploration.
Interventions	Participants were randomly assigned to two groups. Group 1: closed passive drain (n = 100). Group 2: no drain (n = 100). Co‐interventions: Drain brought through: separate wound. Antibiotic use: not stated. Duration of drain: not stated.
Outcomes	The main outcome measures were wound infection, chest infection, and hospital stay.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment?	Low risk	A ‐ Adequate