Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
Postoperative outcomes
Systematic review	3090 people with acute cholecystitis 17 RCTs in this analysis	Proportion of people with wound infection 85/1594 (5%) with drain 51/1496 (3%) with no drain	OR 0.61 95% CI 0.43 to 0.87 P = 0.006	Small effect size	no drain
Systematic review	2128 people with acute cholecystitis 12 RCTs in this analysis	Proportion of people with chest infection 91/1138 (8%) with drain 53/990 (5%) with no drain	OR 0.84 95% CI 0.49 to 1.44 P = 0.52		Not significant