options nocenter ps=65 ls=80; 

title1 'Increasing Variance Example';

data one; 
 infile 'c:\saswork\data\boxcox.dat';
 input trt resp;

proc glm data=one;
 class trt;
 model resp=trt;
 output out=diag p=pred r=res;

title1 'Residual Plot';
symbol1 v=circle i=none;
proc gplot data=diag; 
 plot res*pred /frame;

/* This computes the sample mean (mu) and standard deviation (sigma) at 
   each treatment level and outputs this information to SAS file "two" */
proc univariate data=one noprint;
 var resp; by trt;
 output out=two mean=mu std=sigma;

/* This creates a new SAS data set "three" which contains the natural 
   logs of both the sample means and standard deviations */
data three;
 set two;
 logmu = log(mu);
 logsig = log(sigma);

/* Perform a regression analysis on these log transformed values */
proc reg;
 model logsig = logmu;

title1 'Mean vs Std Dev';
symbol1 v=circle i=rl;
proc gplot;
 plot logsig*logmu;
run;