用SAS做格兰杰检验真是太虐了！
我的代码很简单，
/*--- Causality Testing ---*/
proc varmax data=a;
model x1 x2/ p=1 noprint;
causal group1=(x1) group2=(x2);
causal group1=(x2) group2=(x1);
run;quit;


但是log显示
ERROR: No nonmissing observations. The VARMAX procedure stopped processing further steps.


求求各位大神解读，拜谢了。