Not understood [🇷 for BE/BA]

posted by ElMaestro  – Denmark, 2020-08-05 10:13 (1415 d 10:39 ago) – Posting: # 21824
Views: 14,578

Thanks PharmCat,

funny, I read the ref. you mention (Lindstrom & Bates) yesterday and I did not understand much of it. Will try again.

❝ Problem1: when you have big matrix invercing is slow as hell, but if you inverce by blocks (you can do it because it block-diagonal) it can be done faster.


Sounds neat, will check if I can somehow do such a thing.

❝ Problem2: In BE case you have many equal Zi matrices, so in logREML calculation (if you calc by subject) you inverce one matrix many times (because V = ZGZ'+R, Z can be different, G and R not changing subject by subject). If you cache result - you can seriously increase performance.


My approach is very simple: I make a case for saying that when T is not replicated while R is replicated, then it is not possible to make a meaningful model when V=ZGZt+R (as long as we count on R having the withins and G having the betweens). If we insest on ZGZt+R then we get irrelevant variance components associated with T whichever way we parameterise the covariance matrix. Therefore, I am working in V directly, meaning I am writing the blocks into it directly.
This may still be compatible with your proposal, though.

Pass or fail!
ElMaestro

Complete thread:

UA Flag
Activity
 Admin contact
23,059 posts in 4,841 threads, 1,646 registered users;
34 visitors (0 registered, 34 guests [including 10 identified bots]).
Forum time: 20:53 CEST (Europe/Vienna)

Friends don’t let friends use Excel for statistics!    Jonathan D. Cryer

The Bioequivalence and Bioavailability Forum is hosted by
BEBAC Ing. Helmut Schütz
HTML5