proc freq data=multi order=data;
  weight n;
  table ldose*symptoms / out=os;
  run;
proc transpose data=os out=tran;
  by ldose; var count;
  run;
data a; set tran;
  const=0;
  c1=log((sum(of col1-col1)+const)/(sum(of col2-col3)+const));
  c2=log((sum(of col1-col2)+const)/(sum(of col3-col3)+const));
  run;
proc sgplot;
  series y=c1 x=ldose;
  series y=c2 x=ldose;
  yaxis label="Empirical Logits";
  run;