Hi Alex,

At this stage I don't know for sure. I'm just trying to replicate the SAS model that I have the short description and results for. The results indicate that the model includes the 5 random components I listed, but is that not enough to uniquely identify the model that they used?

I am not familiar with SAS' conventions for MIXED output, but it looks to me that there is are indeed heterogenous time and intercept variance components for each level of period. Is this the feature that SPSS can not handle?

Thanks again, Kylie.

Quoting "Reutter, Alex" <areutter@spss.com>:

> Just to be sure I understand what kind of covariance setup you've got: are > you fitting an AR(1) random effects structure with time and intercept as > effects, and and period as a grouping variable to define heterogenous > variance estimates for time and intercept for each level of period? MIXED > does not explicity support grouping variables, and at the moment I can't > think of a way to trick it into doing so. > > Alex > > > -----Original Message----- > From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of > Kylie Lange > Sent: Friday, July 11, 2008 12:17 AM > To: SPSSX-L@LISTSERV.UGA.EDU > Subject: Re: variance structures in MIXED > > Hi Alex, > > Just to clarify in case I wasn't clear - I'm quite comfortable with running > these kinds of repeated measures mixed models in SPSS. It's just the > additional 'period' difference in variances that I haven't been able to work > out how to define. > > Re your specific questions, the data file is indeed as you illustrate > however all rows with time=1,2 or 3 will have period=1. Subjects underwent > the four conditions in random order. During each condition 23 repeated > measures were taken. > > Thanks again, > Kylie. > > > -----Original Message----- > From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of > Reutter, Alex > Sent: Friday, 11 July 2008 12:54 pm > To: SPSSX-L@LISTSERV.UGA.EDU > Subject: Re: variance structures in MIXED > > What's the structure of your data? Something like: > > subject time condition period response > 1 1 1 1 ### > 1 1 2 1 ### > 1 1 3 1 ### > 1 2 1 2 ### > 1 2 2 2 ### > 1 2 3 2 ### > 1 3 1 2 ### > ... > 1 23 1 2 ### > 1 23 2 2 ### > 1 23 3 2 ### > 2 1 1 1 ### > 2 1 2 1 ### > 2 1 3 1 ### > ... > > Or perhaps time and condition reversed? Precisely how were the experimental > conditions administered (i.e., were subjects assigned a condition and then > followed for 23 time periods, then assigned another condition and followed > for 23 time periods, then the third condition and followed for the final 23 > time periods?) > > Alex > > > -----Original Message----- > From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of > Kylie Lange > Sent: Thursday, July 10, 2008 8:42 PM > To: SPSSX-L@LISTSERV.UGA.EDU > Subject: variance structures in MIXED > > Hi all, > > > > I am trying to replicate some analyses that were originally done in SAS. I > do not have the code that was used, but do have the analysts writeup of the > analysis method and results. I am trying to confirm if the variance > structure they used is also possible in SPSS. > > > > It is a doubly repeated measures design - multiple time points (23) per > experimental condition (3) per subject. The model includes fixed effects for > time (entered as a factor), condition and the time*condition interaction. > The description of the previous analysis includes this statement regarding > the variances: > > > > "Due to different variances in the outcome across time, variances were > estimated separately for baseline measures (the first three time points), > and then for all measures after." > > > > From the output provided I can see that a variable was created ('period') > that equalled 1 for the observations at the three baseline timepoints, and 2 > for all the others. The 'Covariance Parameter Estimates' table from SAS > includes 5 parameters: > > > > Cov Parm Subject Group > > > > Intercept id period 1 > > Intercept id period 2 > > time id period 1 > > time id period 2 > > AR(1) id > > Error > > > > Can anyone suggest how to define this kind of model in SPSS' MIXED > procedure? > > > > Thanks, > > Kylie. > > ===================== > To manage your subscription to SPSSX-L, send a message to > LISTSERV@LISTSERV.UGA.EDU (not to SPSSX-L), with no body text except the > command. To leave the list, send the command > SIGNOFF SPSSX-L > For a list of commands to manage subscriptions, send the command > INFO REFCARD >

===================== To manage your subscription to SPSSX-L, send a message to LISTSERV@LISTSERV.UGA.EDU (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD