Mennigen 1989.

Methods	Sequence generation: random number tables Allocation concealment: not described Blinded: not described
Participants	Inclusion criteria: elective resection, intra‐abdominal anastomosis Exclusion criteria: obstruction, perforation or sepsis present at time of performing anastomosis, i.e. emergency operation Type of disease: 77/100 carcinoma, 6/100 adenoma, 7/100 diverticular disease, 9/100 inflammatory colon disease, 1/100 type of disease not reported (for 1 drop‐out) Type of anastomosis: 59/100 left hemicolectomy, 33/100 right hemicolectomy, 7/100 subtotal colectomy, 1/100 not described Number of participants: 100 Age range: 15‐87 years Gender: 49 male, 50 female Place of study: Germany (single centre) Time of study: June 1984 to November 1986
Interventions	Treatment: silicone drain Control: no drain
Outcomes	Primary outcome: anastomotic dehiscence Secondary outcomes: mortality, surgical re‐intervention, radiological anastomotic dehiscence and wound infection
Notes	Publication: journal article
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Random number tables
Allocation concealment (selection bias)	Unclear risk	No description
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Unclear
Blinding of participants and personnel (performance bias) All outcomes	High risk	No description
Blinding of outcome assessment (detection bias) All outcomes	High risk	No description
Incomplete outcome data (attrition bias) All outcomes	Low risk	Drop‐out 1/100 (1%)
Selective reporting (reporting bias)	Low risk	Reported all outcomes that were pre‐stated in the methods section
Other bias	Unclear risk	No studies reported substantial baseline differences in the treatment and control groups. We found no other potential sources of bias within the included studies Sample size calculation not described. Source of bias