看下这个例子：
SAS gives the likelihood-based pseudo R-square measure and its rescaled measure. Categorical Data Analysis Using The SAS System, by M. Stokes, C. Davis and G. Koch offers more details on how the generalized R-square measures that you can request are constructed and how to interpret them.
proc logistic data = hsb2;
  class prog(ref='1') /param = ref;
  model hiwrite(event='1') = female prog read math / rsq lackfit;
run;


from http://www.ats.ucla.edu/stat/sas/seminars/sas_logistic/logistic1.htm