Open issues [🇷 for BE/BA]

posted by ElMaestro  – Denmark, 2020-08-06 23:11 (1777 d 18:09 ago) – Posting: # 21827
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Hi PharmCat,

I really like your idea. I don't have a good understanding of this as a whole but I know that when I work with a little these things they become easier for me to grasp, so I am giving it a try. :-)

Let us turn to Gurka 2006 equation 3 and 5 and remembering that the rank of our overall design matrix X is 6:
Gurka requires me to derive Xi, the design matrix for fixed effects of subject i.
They mention that "Xi is a (ni × p) known, constant design matrix for the i' th subject
with rank p"

At just three observations per subject we cannot have a rank of p=6 for Xi. The maximum rank is naturally 3. I don't see a way to handle Xi on a subject by subject basis, but perhaps you have some insight. Possibly I could do it by lumping subjects together so that the "smaller" X of sorts still has more rows thank columns and thus a rank of p=6.


Do you see my issue with Xi? Could you indicate your view on Xi here? Is lumping subjects together a way to go to ensure the right rank of the reduced design matrices? Many thanks in advance.
—
Pass or fail!
ElMaestro

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