/* laftemps.sas */
/* regressions of yearly mean mid temp on year */
/* early: 1893-1940 late: 1941-2003 */
options ls=72 ps=60;
data temps;
   infile 'laftemps.dat';
   input obs year type days low high mid;
   early = 1;
   if year > 1940 then early = 0;
   late = 1 - early;
   year1 = year*early;
   year2 = year*late;
   drop obs type days low high;
proc glm data=temps;
   model mid = early late year1 year2 / noint;
      estimate 'Eslope-Lslope' year1 1 year2 -1;
title 'mean mid temperatures: 2 lines';
proc glm data=temps;
   model mid = early late year / noint ss1 ss2 clparm;
      output out=new predicted=yhat residual=resid;
      estimate 'Emean-Lmean' early 1 late -1;
      estimate 'early mean' early 1 year 1916.5;
      estimate 'late mean' late 1 year 1972;
title 'mean mid temperatures: parallel lines';
proc plot data=new;
   plot resid*yhat/vref=0;
run;