Friday, July 20, 2007

Variance-Covariance Matrix in glm

This is a small function Venables and Ripley provide in their MASS book. You don't need it anymore because vcov() has a method for the glm class. However, it is useful to see how to extract bits from a fitted model object.

#return the variance-covariance matrix of a glm object
#from p. 188 in Venables and Ripley. 2002.
#Modern Applied Statistics With S. Springer. New York.
so <- summary(obj,corr=F)
so$dispersion * so$cov.unscaled

Wednesday, July 18, 2007

Visualizing Data

Sometimes it is helpful to see the plots created from the example
files within R libraries. Of course you can paste them directly
into R, but this web page allows you to view the images within the
context of the help files:

R Graphical Manuals

Also, check out this link for the R Graph Gallery.