dredge function error - R package MuMln

Question

I have to do statistical analyses on a data set. I would like to create all the possible models and to test them with the dredge function but it doesn't work. Indeed, when I type:

glm1<-glm(presabs~dca1+dca2+se1+se2, family=binomial(logit))
dredge(glm1)

I got this error:

Erreur in dredge(glm1) : 
'global.model''s 'na.action' argument is not set and options('na.action') is "na.omit"

Can someone help me?

Answer 1

The issue with using options(na.action = "na.fail") is that it changes the global settings of R. If you have a large script, changing the global settings will potentially impact on other sections of your code where you implicitly rely on R's default settings. There are two ways to avoid this:

1. After using dredge change the settings back via options(na.action = "na.omit").

OR the better way...

2. Utilise the regression function's ability to set the na.action argument. In your case:

glm1 <- glm(presabs ~ dca1+dca2+se1+se2,
            family=binomial(logit),
            na.action = "na.fail")

Answer 2

See ?dredge:

# Example from Burnham and Anderson (2002), page 100:
data(Cement)
options(na.action = "na.fail")   #  prevent fitting models to different datasets

fm1 <- lm(y ~ ., data = Cement)
dd <- dredge(fm1)

If you skip the second line, your described error pops up, as the models are fitted to different datasets (due to removal of NAs).