Statistical analysis
Categorical variables were expressed as frequencies and percentages
(%), and continuous variables were expressed as mean ± standard
deviation (SD). The Shapiro–Wilk test was used to assess the normality
assumption for the continuous variables. The Student’s t-test or
Mann–Whitney U test was used between groups, whether the statistical
hypotheses were fulfilled or not. The Chi-squared test was used to
compare the distribution of categorical variables in groups. Simple
logistic regression was used for bivariate analysis to identify
individual associations with stone-free status (Yes/No), hospitalization
time (1 day versus more than 1 day) and postoperative complications
(Yes/No). A p value of < .25 was accepted as significant in
the selection of the factors whose efficacy would be assessed with
multiple logistic regression analysis, which was performed stepwise.
Significant results are presented as odds ratios (ORs) and 95%
confidence interval (CI). Multiple regression was run to predict
operation time. Non-significant covariates were removed from the model.
There was linearity as assessed by a plot of studentized residuals
against the predicted values. The area under the receiver operating
curve (AUC) was calculated. All statistical analyses were performed
using SPSS 19.0 software (IBM Corp., Armonk, NY, USA). All statistical
tests had a statistical significance level of p value < .05
(two-tailed).