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In developing a formula for manual use in clinical settings, simplicity is as important as accuracy. Whole-liver (WL) mass is often estimated using demographic and anthropometric information to calculate the standard liver volume or recommended graft volume in liver transplantation. Multiple formulas for estimating WL mass have been reported, including those with multiple independent variables. However, it is unknown whether multivariable models lead to clinically meaningful improvements in accuracy over univariable models. Our goal was to quantitatively define clinically meaningful improvements in accuracy, which justifies an additional independent variable, and to identify an estimation formula for WL graft weight that best balances accuracy and simplicity given the criterion. From the Japanese Liver Transplantation Society registry, which contains data on all liver transplant cases in Japan, 129 WL donor-graft pairs were extracted. Among the candidate models, those with the smallest cross-validation (CV) root-mean-square error (RMSE) were selected, penalizing model complexity by requiring more complex models to yield a ≥5% decrease in CV RMSE. The winning model by voting with random subsets was fitted to the entire dataset to obtain the final formula. External validity was assessed using CV. A simple univariable linear regression formula using body weight (BW) was obtained as follows: WL graft weight [g] = 14.8 × BW [kg] + 439.2. The CV RMSE (g) and coefficient of determination (R2) were 195.2 and 0.548, respectively. In summary, in the development of a simple formula for manually estimating WL weight using demographic and anthropometric variables, a clinically acceptable trade-off between accuracy and simplicity was quantitatively defined, and the best model was selected using this criterion. A univariable linear model using BW achieved a clinically optimal balance between simplicity and accuracy, while one using body surface area performed similarly.

To assess the use of laparoscopic surgeries (LS) and the association between its performance and hospitals' preference for LS over open surgeries.LS is increasingly used in many abdominal surgeries, albeit both with and without solid guideline recommendations. To date, the hospitals' preference (LS vs. open surgeries) and its association with in-hospital outcomes has not been evaluated.We enrolled patients undergoing 8 types of gastrointestinal surgeries in 2011-2013 in the Japanese National Clinical Database. We assessed the use of LS and the occurrences of surgery-related morbidity and mortality during the study period. Further, for 4 typical LS procedures, we assessed the hospitals' preference for LS by modeling the propensity to perform LS (over open surgeries) from patient-level factors, and estimating each institution's observed/expected (O/E) ratio for LS use. Institutions with O/E>2 were defined as LS-dominant. Using hierarchical logistic regression models, we assessed the association between LS preference and in-hospital outcomes.Among 1,377,118 patients undergoing gastrointestinal procedures in 2,336 participating hospitals, use of LS increased in all 8 procedures (35.1% to 44.7% for distal gastrectomy (DG), and 27.5% to 43.2% for right hemi colectomy (RHC)). Those operated at LS-dominant hospitals were at an increased risk of operative death (OR 1.83 [95%CI, 1.37-2.45] for DG, 1.79 [95%CI, 1.43-2.25] for RHC) compared to standard O/E level hospitals (0.5≤O/E