2.3. Statistical analysis
Stepwise multiple linear regression was performed to identify the best predictor among various parameters of the IOS by using height, age, body weight, and gender as potential independent variables. The 5th percentile and 95th percentile was calculated using parametric methods. All statistical analyses were performed using IBM SPSS Statistics version 20 (IBM, Armonk, NY, USA).P <0.05 was considered statistically significant.