[R] Multiple comparisons when interacction

Jorge Lampurlanes Castel jlampur at eagrof.UdL.es
Tue Jan 30 19:27:23 CET 2007

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

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

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