Peterli 2012.

Methods	Parallel randomised controlled clinical trial Randomisation ratio: not reported Superiority design
Participants	Inclusion criteria: BMI > 40 kg/m2 or BMI > 35 kg/m2 with presence of at least one comorbidity, age 18‐65 years, failure of conservative treatment over 2 years. Exclusion criteria: contraindications to major abdominal surgery, severe symptomatic gastro‐oesophageal reflux disease despite medication, large hiatal hernia, expected dense adhesions at the level of the small bowel, the need for endoscopic follow‐up of the duodenum, patients with inflammatory bowel disease. Diagnostic criteria: BMI > 40, or BMI > 35 with comorbidity.
Interventions	Number of study centres: 4 Treatment before study: not reported Titration period: not reported Interventions: 1: Laparoscopic Roux‐en‐Y gastric bypass (LRYGB) 2: Laparoscopic sleeve gastrectomy (LSG) Stated that vitamin supplementation and postoperative thrombosis prophylaxis were performed according to the policy of each participating centre (no further details reported).
Outcomes	Outcomes reported in abstract of publication: weight loss, co‐morbidities, complications and additional procedures
Study details	Run‐in period: not reported Study terminated before regular end: no; however, note that follow‐up was intended to be 5 years but to date results have only been published up to 1 year for most outcomes and 3 years for weight and BMI; at the time of analysis, median follow‐up was 2 years.
Publication details	Language of publication: English Funding: commercial and non‐commercial Publication status: peer reviewed journal
Stated aim for study	Quote: “… to perform a large multicentre RCT assessing the efficacy and safety of LSG and LRYGB…” (Peterli in press, p.4)
Notes	BMI: body mass index; LSG: laparoscopic sleeve gastrectomy; LRYGB: laparoscopic Roux‐en‐Y gastric bypass; n/a: not applicable
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote from publication: "Patients were assigned to either LSG or LRYGB using a computer based randomization with sealed envelopes"
Allocation concealment (selection bias)	Unclear risk	Comment: sealed envelopes were used, but it is unclear if they were sequentially numbered
Blinding of participants and personnel (performance bias) All outcomes	High risk	Comment: no information about blinding provided. ClinicalTrials.gov record describes the trial as ‘open label’
Blinding of outcome assessment (detection bias) All outcomes	High risk	Comment: no information about blinding provided. ClinicalTrials.gov record describes the trial as ‘open label’
Incomplete outcome data (attrition bias) Weight	Unclear risk	Comment: data presented are for an interim analysis during an ongoing study. Follow‐up data not presented for all the patients randomised – this is probably because it is not available yet as data is for an interim analysis at one year, but this is not fully explained in the publication (i.e. no information about the number of participants who had completed one‐year follow‐up)
Incomplete outcome data (attrition bias) Quality of life	Unclear risk	Comment: authors have not provided the number of patients included in the quality of life analysis. This is an interim analysis
Incomplete outcome data (attrition bias) Comorbidities	Unclear risk	Comment: authors have not provided the number of patients included in the co‐morbidities analyses. This is an interim analysis
Selective reporting (reporting bias)	Unclear risk	Comment: results for outcomes pre‐specified in the protocol have been reported. The only measure pre‐specified that results were not provided for was an additional measure of quality of life, BAROS QoL, and the authors explained in their answers to our request for clarifications that data were not provided for this as not all study centres delivered the results. BAROS QoL data are provided in a conference abstract for a small number of patients only
Other bias	High risk	Comment: interim analysis, that does not present data on all patients randomised.