Re: UN vs. UNR [was Re: SPSS Syntax MIXED Model]

Posted by Ryan on
URL: http://spssx-discussion.165.s1.nabble.com/SPSS-Syntax-MIXED-Model-tp5713934p5714093.html

Alex,

 

The abbreviated answer is that I misspoke previously. In general, yes, UNR should simply be a reparameterization of UN. I do know that there have been reported incidents where the MIXED procedure in SAS has produced different results. However, I have never encountered that phenomenon in SPSS. Frankly, those inconsistencies reported from the MIXED procedure in SAS had nothing to do with why I suggested to use UN instead of UNR. However, a quick simulation experiment shows that my thinking was off as to what would happen to the elements along the main diagonal. No time to discuss or explore further.

 

The idea of fitting a growth curve via a random coefficient regression model is an interesting topic, and I believe that a detailed discussion around its utility can push the boundaries a bit as to what's been discussed on SPSS-L previously regarding some of the real potential of the MIXED procedure in SPSS. I'll try to kick start such a discussion sometime in the near future.

Best,

 

Ryan

 

On Tue, Jul 3, 2012 at 9:00 AM, Alex Reutter <[hidden email]> wrote:

Regardless of how the conversation with the OP unfolds, I'd be interested in your thoughts on this when you have time.  UNR should simply be a reparameterization of UN that yields the same model, but perhaps there are some cases where that breaks down?

Cheers,
Alex




From:        R B <[hidden email]>
To:        [hidden email]
Date:        07/02/2012 07:35 PM
Subject:        Re: SPSS Syntax MIXED Model
Sent by:        "SPSSX(r) Discussion" <[hidden email]>

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I might take issue with using a "UNR" structure instead of
a "UN" structure to start but I'll save my reasoning for another time.