例によって
getS3method("vif", "lm")
などと内部をみてみると
(getS3method("vif", "glm") は定義されていなかった)，
function (mod, ...)
{
if (any(is.na(coef(mod))))
stop("there are aliased coefficients in the model")
v <- vcov(mod)
assign <- attributes(model.matrix(mod))$assign
if (names(coefficients(mod)[1]) == "(Intercept)") {
v <- v[-1, -1]
assign <- assign[-1]
}
else warning("No intercept: vifs may not be sensible.")
terms <- labels(terms(mod))
n.terms <- length(terms)
if (n.terms < 2)
stop("model contains fewer than 2 terms")
R <- cov2cor(v)
detR <- det(R)
result <- matrix(0, n.terms, 3)
rownames(result) <- terms
colnames(result) <- c("GVIF", "Df", "GVIF^(1/(2*Df))")
for (term in 1:n.terms) {
subs <- which(assign == term)
result[term, 1] <- det(as.matrix(R[subs, subs])) * det(as.matrix(R[-subs,
-subs]))/detR
result[term, 2] <- length(subs)
}
if (all(result[, 2] == 1))
result <- result[, 1]
else result[, 3] <- result[, 1]^(1/(2 * result[, 2]))
result
}
<bytecode: 0xa729af0>
<environment: namespace:car>
……
ってなかんじで，
family = gaussian
にだけ対応しているように見えるんだけど，
どうなんだろう?
