Date:         Sat, 14 Mar 2009 14:31:43 -0700
Reply-To:     KW <kristenw3@YAHOO.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         KW <kristenw3@YAHOO.COM>
Organization: http://groups.google.com
Subject:      proc mixed - predicted values the same
Comments: To: sas-l@uga.edu
Content-Type: text/plain; charset=ISO-8859-1

I am running a Proc mixed to look at the effects of a procedure on 11
animals on 7 different behaviors over 4 days (day is the repeated
variable). I am working with proportion data and performing an arcsine
sq. root transformation on the data since some of the values lie
outside the .3-.7 range. I run each of my dependent variables in
separate mixed models. When I plot my residuals everything looks
great, however when I plot my residual vs. predicted values for 3 of
my behaviors I am getting predicted values that are the same for each
day. The raw data looks fine, no missing values. I am wondering why
SAS calculates the same predicted values for each day for the
particular behaviors? I also get in the log statement that the G
matrix is not positive definite. I have changed the covariance
structure from ar(1) to cs, un, and simple, however the predicted
values are still the same. Does anyone have any suggestions for why
the predicted values might be the same for each day and what type of
covariance structure might help to correct this?

Thanks!
Kristen