Logistic Regression: number of positives and negatives

[Svetlomir Kasabov]

Hello,

I plan using logistic regression for predicting the probability that a 
patient will be given a drug Y. The problem is, that patients don't get 
that drug so often and I have many more training examples with Y=0 than 
examples  with Y=1. Do you think I should keep the number of negative 
examples equal to that of positive examples? Or should I ignore that 
number difference and give my logistic regression model all of the 
training examples ?

Thanks!

Svetlomir.