Re: [R] Multiple comparisons when interacction

From: Jorge Lampurlanes Castel <jlampur_at_eagrof.UdL.es>
Date: Tue 30 Jan 2007 - 18:27:23 GMT

As I understand from the WoodEnergy example in package HH, You are proposing to compute a separate lm for each level of YEAR factor to compare TIL means.
This is the way I used to do this kind of analysis.

But now, it is also possible, with PROC GLM, to adjust only the general model (variable ~ BLOC + TIL * YEAR ) and then to compare TIL means inside every YEAR with the SLICE option.

I am not statistician but I think the difference is that, in the first approach, we use a different error term for every YEAR, whereas in the second approach, we use the same error term for all comparisons.

Perhaps the differences between both approaches are negligible. If not, it is possible to do this analysis in R?

Thanks a lot.

-- 
**************************************************
Jorge Lampurlanés Castel
Departament d'Enginyeria Agroforestal
Escola Tècnica Superior d'Enginyeria Agrària
Universitat de Lleida
Avinguda Rovira Roure, 191
25198-LLEIDA
SPAIN

Tl.: +34 973 70 25 37
Fax.:+34 073 70 26 73
e-mail: jlampur@eagrof.udl.es

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Received on Wed Jan 31 06:46:03 2007

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