我也不知咋回事，于是google了一下，发现估计是因为因素只有2个水平导致的。

Mauchly's test is assessing the condition of sphericity, which is when the variance of differences between levels of repeated measures factors are equal. It is a way of addressing assumptions about the structure of the covariance matrix in repeated measures designs.

If all your repeated measures factors have only two levels, there is only one covariance for each repeated measure. Therefore, the assumption about the covariance matrix is always met and a test of sphericity is not relevant. Unfortunately, the GLM command of SPSS appears to print the test of sphericity even under these conditions, which creates the confusion you seem to be having.

嗯 也认为如果因素水平小于3，球形度检验的结果就不显示。