Grouping binary data
On Thu, 19 Jun 2003, Henric Nilsson wrote:
Dear all, I'm analyzing a binary outcome using glm() with a binomial distribution and a logit link, and have now reached the point where I'd like to do some model checking. Since my data are in binary form I'd like to collapse over the cross-classification of the factors before the model checking. Are there any nice and simple ways doing this? If so, how? If not, I'd be grateful for receiving some hints on how this can be accomplished.
Look at loglm1.data.frame in package MASS, or xtabs: each work by setting up a suitable call to table. If you want to sum up over cases with the same factors (not what is usually meant by collapsing), take a look at multinom (package nnet) which has options to do this for multinomials (and Bernoulli is a special case).
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595