[R] How to use quasibinomial?
Henric Nilsson
hennil at statisticon.se
Fri Jul 4 18:33:45 CEST 2003
I think I can now answer my own questions:
Henric Nilsson (hennil at statisticon.se) wrote*:
>1. I can't seem to get the correct p-values from anova.glm() for the F-tests when
>supplying the dispersion argument and having fitted the model using
>family=quasibinomial.
Using family=quasibinomial does exactly what it says: It fits a quasi-likelihood
model with mean=mu and variance=mu(1-mu). Hence, supplying the dispersion argument
results in R treating this as a known value, i.e. not estimated from data, in which
case the F-test shouldn't be used and therefore returns the same p-value as the Chi-
squared test.
>2. When using summary.glm() on a glm object fitted using family=quasibinomial the
>reported tests are t-tests. Why?
This makes sense since we're estimating the dispersion parameter. Can't really
remember what confused me here...
//Henric
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