topic Re: Split plot repeated measures help? in Statistical Procedures

Split plot repeated measures help?

Tree — Wed, 27 May 2015 22:02:39 GMT

I am working on sas code to test for treatment effects on soil pH through time.

I have 4 plots (reps), two of which are fertilized, and two that are not fertilized (Treat)

1/2 of each plot was plowed (plow)

I measured soil pH at four uneven time intervals (DOY), so end up with 32 data points.

Here is the code I developed - am I missing something? Thanks!

proc mixed data=soil; class treat plow reps doy;

model pH = treat|plow|doy / Lcomponents;

repeated doy / sub=treat type=cs;

run;

Re: Split plot repeated measures help?

plf515 — Thu, 28 May 2015 10:56:49 GMT

Looks OK to me

Re: Split plot repeated measures help?

SteveDenham — Thu, 28 May 2015 18:21:13 GMT

I agree with Peter, the code formulation is perfect. I would hesitate on specifying a compound symmetry error structure, as it assumes equal correlations between days, no matter how far separated in time, and equal covariances at each time point. However, because of the small N for timepoints, and unequal spacing in time, this may be the only candidate that will be able to be fit.

Steve Denham

Re: Split plot repeated measures help?

Tree — Fri, 29 May 2015 14:22:57 GMT

Thanks!