Hi Colleagues,
I have gone through Sphericity Tests in RMD using SAS Proc GLM, and have used SAS Proc Mixed to analyse RM experiments as well. My question is how to pupulate the Greenhouse-Geisser (G-G) and the Huynh-Feldt (H-F) adjustments in Proc Mixed procedure SAS results if sphericity fails in the data set. Kindly share the code or explanation please.
Specifying TYPE=HF in the REPEATED statement can accomplish this. However, I suspect you missed the point I was trying to make. Consider other covariance structures - I really doubt that HF will lead to the smallest corrected AIC - it will probably not be the best fit for your model. This avoids making a sphericity assumption, which is really not necessary (see the chapter on Repeated Measures in any edition of SAS for Mixed Models for a discussion).
SteveDenham
Hello,
Does this paper help?
Comparing the SAS GLM and MIXED Procedures for Repeated Measures
Russ Wolfinger and Ming Chang, SAS Institute Inc., Cary, NC
https://support.sas.com/rnd/app/stat/papers/mixedglm.pdf
( Russ Wolfinger is the original developer of PROC MIXED. )
Koen
One of the reasons for using PROC MIXED is that the F tests are valid whether or not the sphericity assumption is met, provided a valid covariance structure is fit and that there are no issues with the convergence. If you are truly concerned about sphericity, then you should stick with PROC GLM, and not use ML/REML methods.
SteveDenham
Specifying TYPE=HF in the REPEATED statement can accomplish this. However, I suspect you missed the point I was trying to make. Consider other covariance structures - I really doubt that HF will lead to the smallest corrected AIC - it will probably not be the best fit for your model. This avoids making a sphericity assumption, which is really not necessary (see the chapter on Repeated Measures in any edition of SAS for Mixed Models for a discussion).
SteveDenham
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