老师,我新发现"wald chiz()" 显示的字体是浅蓝色,而不是通常的绿色,于是点击了一下,并得到了如下信息:
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The F or chi2 model statistic has been reported as missing
    Your estimation results show a F or chi2 model statistic reported to be
    missing.  Stata has done that so as not to be misleading, not because
    there is something necessarily wrong with your model.
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但还是不明白为什么怕misleading.