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
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;
model spp_rate = year;
means year / hovtest welch;