请问SAS中proc mixed为什么没有Rsquare的输出？ 理论上可以自及计算吗？

请问SAS中proc mixed为什么没有Rsquare的输出？ 理论上可以自及计算吗？有谁可以提供一下现成的程序吗？

如果没有Rsquare怎么判断模型好坏呢？

You can calculate Rsquare based on Wald statistics or Likelihood Ratio. But we do not use that often.
Usually, we use AIC/BIC/Likelihood Ratio to evaluate the fitness of the model.
In SAS, you can find these statistics under Fit Statistics.
When you want to compare nested models, Likelihood Ration Test is good and it can provide you the significant level.
When you want to compare models that are not nested, AIC/BIC are good. You just choose the small one. In SAS, the smaller is better.