CART®

The original CART monograph discusses a study the authors performed working with 215 observations and 19 predictors, where 37 records were of class 1 and 178 of class 0. We think that this is example, with 37 examples in the smaller class is close the smallest sample size you can usefully work with CART.

Recommendation: We suggest using a minimum of 100 records, with the target variable distributed not more unbalanced than in proportions (1/3, 2/3) for up to 30 predictors. We recommend repeated cross-validation to estimate the out-of-sample (previously unseen data) performance.