There are now newer statistical methods to compare two or more groups in an observational study in a good and statistically significant manner and Stata version 13 can handle it well by matching the so-called covariates (e.g., in our study may be covariates following variables at baseline: age, gender, preoperative weight, BMI, concomitant disease such as diabetes). Patients were matched and then the comparison is done between the matched groups. Calculation of treatment effects , including so-called propensity score exploitation has already been used in a comparative study between GBP and other bariatric surgery for obesity where neither has been able to randomize patients (Carlin et al Annals of Surgery, Vol. 257, Number 5, May 2013: 791-7)