V [R for BE/BA]

posted by ElMaestro  – Denmark, 2011-01-28 12:14 (3918 d 12:34 ago) – Posting: # 6507
Views: 62,891

Dear d_labes,

» where are the intra-individual (error or residual) variances or sd for Test and Reference?
» You have only one residual.
» The trt1 and trt2 variances (and corr) in your output are the between subject covariance parameter.

Interesting. Let us discuss for a moment the covariance matrix V (not Z and not G, and at this point also not discussing which syntax SAS applies for the given problem (leaves disussions about CSH, FA(0) out here)).
V holds the key.
Further, let us assume for simplicity we only look at the first subject which is the first 4x4 of V where the data are ordered as TRTR (i.e. per1-per2-per3-per4 for the first subject; in the original dataset above they were ordered differently but the order in this context does not change the point):

Data in per1 and per3 correlate within the subject as (s)he gets T (within variance VT).
Data in per2 and per4 correlate within the subject as (s)he gets R (within variance VR).
To this we add a common error variance on the diagonal (V0).

Having no particular mathematical understanding, the first 4x4 of V I think will be:
V0+VT     0         VT       0
0         V0+VR     0        VR
VT        0         V0+VT    0
0         VR        0        V0+VR


Both of the models discussed above correspond to a fit with this V, as far as I can see.

Pass or fail!
ElMaestro

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