Data analysis
The statistical analyses were performed using PASW Statistics for Windows, version 18.0 (SPSS Inc., Chicago, IL, USA) and Stata, version 15 (StataCorp LLC., College Station, TX, USA). The demographic data were analyzed with descriptive statistics.; the categorical data were expressed as number (%), whereas the continuous data were presented as mean (± standard deviation). The Kaplan–Meier method was used to examine the time to improvement during follow-up, while Cox regression was employed to analyze the correlated time-to-event data. After a univariable analysis was performed, the selection of variables for a multivariable analysis was based on a univariable p-value of < 0.1. Results were shown as adjusted hazard ratio (HR), 95% CI, and p-value. P-values of < 0.05 were considered statistically significant.