Thanks for your answer. I appreciate it.
As I said, I got four equations (by M ) from the four different methods and I would like to plot the predicted values from all the four equations in one graph, join them and show the trends. With your proposal SAS disabled the By statement.
proc reg outest=est1 outsscp=sscp1 data=WDDGS.fractionsWDDGS24;
eq1: model Y=PS;
eq2: model Y=PS PSSQ / r cli clm;
plot Y*PSsq='a' predicted.*pssq='p' u95.*pssq='u' l95.*pssq='1' / overlay;