Programming the statistical procedures from SAS

Proc MIXED with a repeated measure and nested factor

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Proc MIXED with a repeated measure and nested factor

[ Edited ]

I have a split-plot design: main-plot is fertilizer (Fert), sub-plot is the presence or absence of an N-fixing species (Nfix). We are testing the flux of gases from the soil. I have used PROC MIXED to analyze this design and that worked fine. Additionally, we included a Repeated statemnet due to measuring the same plots 4 times.

The complications arise when introducing what i believe is a hierarchical twist. In the Nfix sub-plot, i sampled by tree species: in both the Y and N levels of Nfix 2 trees were selected for sampling, with I and nI in the Y treatment and n1 and n2 in the N treatment.

I used the following code and the results do not return any value for Nfix or any interactions including Nfix. Additionally, all LSMeans values returned are P<0.00001, which absolutely cannot be true. PROC MIXED correrctly identifies 3 DF for the Fert level, but incorrectly assigns 497 DF for everything else.

So, how can i write a code that will correctly identify the DF in this split-plot analysis that includes the analysis by tree type in the sub-plot?

 


proc mixed;
Class Block Fert Nfix Tree Date PlotID;
Model logCH4=
Fert
Nfix
Tree
Fert*Nfix
Date
Date*Fert
Date*Nfix;
Random Block Fert*Block;
Repeated Date / subject=plotID Type=CS;
lsmeans Fert Nfix Nfix*Fert Date Date*Fert Date*Nfix/pdiff adjust=tukey;
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