libname sasdata2 "e:\sasdata2";

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

data sasdata2.autism_socialization_lag;
  set sasdata2.autism_socialization;

  by newinit;

  lagvsae = lag1(vsae);
  lagage  = lag1(ageauto);

  if first.newinit then do;
     lagvsae=.;
	 lagage=.;
  end;

  change_vsae = vsae-lagvsae;

  ageyears=ageauto/12;
  lagageyears=lagage/12;
  change_years = ageyears-lagageyears;

  rate_vsae_chg = change_vsae/change_years;

  drop lagageyears change_years lagvsae change_vsae;
  
run;

proc print data=sasdata2.autism_socialization_lag(obs=30);
*var newinit cohort ageyears lagageyears change_years 
            vsae lagvsae change_vsae rate_vsae_chg;

run;

proc means data=sasdata2.autism_socialization_lag;
  where cohort in (3,5,9,13);
  class cohort;
  var rate_vsae_chg;
run;