[R] delta-beta's

[JEB Halliday]

Hi there

I have created a multivariate logistic regression model looking at the
presence/absence of disease on farms.  I would like to plot the diagnostic
plots recommended by Hosmer & Lemeshow to look particularly for any points of
high influence.  In order to do this I need to extract values for delta-beta.
The function dfbeta gives a value for change in each coefficient but I am
looking for a composite value that gives an overall measure of change to the
coefficients.  It may be that dffits is this function but I cannot gather what
this is or what it is calculated from?

If anyone has any advice re plotting H&L logistic regression diagnostics in R
that would be greatly appreciated.
Also, can any of these functions be applied to glmmPQL mixed models?

Thanks very much
Jo Halliday