libname sasdata2 "e:\sasdata2\";

proc sort data=sasdata2.autism_demog ;
  by newinit;
run;

proc sort data=sasdata2.autism_socialization ;
  by newinit cohort;
run;

data sasdata2.autism_combined;
  merge sasdata2.autism_demog(in=a)  
        sasdata2.autism_socialization(in=b);
  by newinit;
  if a and b;
run;