Statistical analysis
SPSS 15.0 for Windows was used for statistical analysis. Descriptive statistics were given as numbers and percentages for categorical variables, and as median and interquartile range for numeric variables. The rates in independent groups were compared using the Chi-Square Test. When the numerical variable did not meet the normal distribution condition, comparisons of two independent groups were made using the Mann Whitney U Test. Relationships between numerical variables were analyzed using Spearman Correlation Analysis. Statistical significance level of alpha was accepted as p <0.05.