```Date: Tue, 11 Dec 2001 19:15:30 -0800 Reply-To: Scott Marion Sender: "SAS(r) Discussion" From: Scott Marion Organization: http://groups.google.com/ Subject: PROC MIXED code for split-plot ANOVA? Content-Type: text/plain; charset=ISO-8859-1 SAS users, I'm seeking help with the appropriate SAS code for an analysis. Any assistance will be greatly appreciated. The analysis is a split-plot ANOVA design with two between-subjects factors and one within-subjects factor, but since the term 'split-plot' seems to mean different things to different people, I'll specify it as clearly as possible: The data are abundances of animals in vegetated plots at two sites. There are three plot sizes, with three replicates of each plot size at each site for a grand total of 18 plots. In every plot, two estimates of animal abundance are made: one near the edge and one near the interior of the plot. So in split-plot parlance SITE and SIZE are between-plots factors, and POSITION is the within-plots factor. All three factors are fixed. There are no missing cells. I have heard that in a split-plot design PROC GLM does not estimate standard errors for the within-subjects factor and its interaction, so I've been pointed toward PROC MIXED. Considerations: (1) I'd like to include a covariate (plant density). (2) If the SITE*SIZE interaction is significant, I plan to analyze each site separately. How would the code change? (3) If Proc Mixed is the answer, is it capable of creating an output table with the analysis results (as can be accomplished in Proc GLM with the 'outstat=' option)? (4) When structuring the dataset, should I include a unique identifier for each plot (as in the first case below), or will the procedure interpret the correct relationship between the variables if instead I designate replicates 1, 2, and 3 within each site (as in the second set): | PLOT# SITE SIZE POSITION | SITE SIZE REP POSITION 1 1 small edge | 1 small 1 edge 1 1 small interior | 1 small 1 interior 2 1 small edge | 1 small 2 edge 2 1 small interior | 1 small 2 interior 3 1 small edge |vs. 1 small 3 edge 3 1 small interior | 1 small 3 interior 4 1 med edge | 1 med 1 edge 4 1 med interior | 1 med 1 interior 5 1 med edge | 1 med 2 edge etc... | THANKS MUCH for any help; I could wander around in the manuals for a long time without resolving this. -Scott Marion smarion@vims.edu [posted to comp.soft-sys.sas and sci.stat.consult] ```

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