Statistical methods; Statistical analysis were performed usingstatistical SPSS software, x2 test? nonparametic Mann - Wilcoxon test, linear regression were used.

• 六、统计：应用 SPSS统计分析软件，两组间率的比较用 x‘检验，MFI的比较用秩和检验，MFI经对数转换后用一元线性回归法分析其与PI之间的相关性。·2·结 果