SAS9.2 statistical analysis software was used for the calculation of all the statistical analyses. The number of cases, mean, standard deviation, median value, maximal value and minimal value should be calculated for the descriptions of the qualitative parameters. Number of cases and percentages are used for the descriptions on the classification parameters.Two side test is used for all the statistical tests, P<0.05 indicates that the difference is statistically significant (unless indicated otherwise), and 95% confidence is used as the confidence interval.