Sample size and statistical analysis
SD
The study sample size was calculated based on the result of a pilot study. The mean postoperative 48 h cumulative morphine consumptions were (16.8 ± 13.5) mg in the paravertebral block group and (32.7 ± 19.2) mg in the control group. Thirty-five patients were required in each group to achieve an α level of 0.01 and β level of 0.9. Considering possible dropouts, a total of 80 patients were enrolled.Statistical analysis was performed using SPSS for Mac version 23.0 (IBM Corp., Armonk, NY, USA). Normality was tested using the Q-Q plots. Normally distributed variables were expressed as mean ± SD, non-normally distributed variables were expressed as median (quartile), and categorical variables were expressed as frequency (percentage). Normally distributed continuous data were analyzed using the independent 