[R] delta AIC for models with 2 variables using MuMIn

[Gavin Simpson]

On Tue, 2010-10-12 at 19:37 +0800, elaine kuo wrote:
> Dear List,
> 
> I want to ask a AIC question based on package library(MuMIn)
> 
> The relative importance of 16 explanatory variables
> 
> are assessed using delta AIC in a generalized linear model.
> 
> 
> Please kindly advise if it is possible to show models

Using the below example you quote:

dd <- dredge(lm1, subset = X1 & X2)

> 
> with any two only certain variables.

If you are now going to ask how can I select only those models with two
variables in, this:

dd <- dredge(lm1)
parms <- !is.na(dd[, -c(1, (ncol(dd) - c(0:7)))])
want <- which(rowSums(parms) == 2)
dd[want, ]

will do it, again using the example you quote.

HTH

G

> Thank you.
> 
> 
> Elaine
> 
> I asked a similar question and got a great help for models
> 
> with only one variable as below.
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> In effect, you want
> 
> data(Cement)
> lm1 <- lm(y ~ ., data = Cement)
> dd <- dredge(lm1, subset = X1)
> 
> want <- with(dd, is.na(X) & is.na(X2) & is.na(X3) & is.na(X4))
> want
> ## how many models selected?
> sum(want)
> ## OK selected just 1, show it
> dd[want, , drop = FALSE]
> 
> Oh, actually, I suppose you could automate this, so it will return all
> models with single variable:
> 
> dd <- dredge(lm1)
> parms <- !is.na(dd[, -c(1, (ncol(dd) - c(0:7)))])
> want <- which(rowSums(parms) == 1)
> dd[want, ]
> 
> Having said all this, I don't think this is a good way to do model
> selection.
> 
> G
> 
> 	[[alternative HTML version deleted]]
> 
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