A Wald test calculates a Z statistic, which is:
z=b/se
This z value is then squared, yielding a Wald statistic with a chi-square distribution. However, several authors have identified problems with the use of the Wald statistic. Menard (1995) warns that for large coefficients, standard error is inflated, lowering the Wald statistic (chi-square) value. Agresti (1996) states that the likelihood-ratio test is more reliable for small sample sizes than the Wald test.
註：wald開平方根 可得z值
參考網址：http://online.sfsu.edu/~efc/classes/biol710/logistic/logisticreg.htm