Symmetric Measures
                                                  Value        Asymp. Std. Errora         Approx. Tb      Approx. Sig.
Ordinal by Ordinal Gamma        0.544                  0 .060                       8.043                0.000
N of Valid Cases                         400   
a. Not assuming the null hypothesis.
b. Using the asymptotic standard error assuming the null hypothesis.

如上,在伽玛值分析的输出结果中, Asymp. Std. Errora ,Approx. Tb,Approx. Sig,分别代表什么意思,还有底下a,b的注解是什么意思...