[R] problem in a glm model.
Simona Avanzo
ibanez27 at inwind.it
Sat Apr 26 00:32:31 CEST 2003
Hallo all,
I have a problem in a glm model.
The glm model has, among the other variables, 4 dummy variables:
flg.a2 (takes values 0 or 1)
flg.d.na2 (takes values 0 or 1)
flg.v2 (takes values 0 or 1)
flg.cc2 (takes values 0 or 1)
In addition to these variables, I have included their interaction, with the order:
(flg.a2+flg.d.na2+flg.v2+flg.cc2)^2
In the model´s summary there are not some interactions (flg.a2:flg.cc2 e flg.d.na2:flg.cc2), because there are not cases that present these interactions.
Then, the model´s summary shows that the p-value of the interaction flg.a2:flg.d.na2 is 0.66, and so this interaction can be eliminated.
But when I apply the test anova between the model whit this interaction and the model without this interaction, the p-value is 0.004, and so, the interaction is significative.
Why I obtain this difference?
Many thanks for any help,
Simona
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