Date:         Wed, 13 Apr 2011 13:59:53 -0400
Reply-To:     Trish Bous <tboussard@GMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Trish Bous <tboussard@GMAIL.COM>
Subject:      barletts test

Hi All,

I was looking for some help to test changes in variance.

I have a hospital rates for a disease over 5 years.  I want to see if the
variance over time is decreasing.

If I had 2 years I would use a ttest and look at the ftest.

However, as I am looking over several years, I am using a GLM, i am using
the HOVTEST, which just tells me that the variances are different.  Is there
a way to see if there is a decreasing trend in the variances?

Thanks for the help!


proc glm data = tmp;
   class year;
   model spp_rate = year;
 means year / hovtest welch;
run;
quit;