[R] Classification with GBM and imbalanced class sizes

Hi all I'm dealing with a supervised binary classification issue. I'd like to use the GBM package to classify individuals as uninfected/infected. I have 15 times more uninfected than infected individuals. I was wondering if GBM models suffer in the case of imbalanced class sizes? I didn't find an

[R] Classification of Cluster-Correlated data

Dear R-Help, I'm dealing with a supervized binary classification issue. My dataset is composed of 1500 individuals, living in 600 households. I have approximately 4000 variables to classify my subjects as "infected/uninfected". I was wondering how would it be possible to account for the hierarchi