Improving Generalization Error Estimates Alexander Nicholson Learning Systems Group California Institute of Technology Pasadena, CA, 91125 Abstract: We introduce an algorithm for estimating the out-of-sample error for a learning problem without reserving a large independent test set. Existing theoretical results are used for the estimates, but are not directly applicable to a practical problem. We show how to use a two stage learning process to overcome the limitation of a random learning algorithm and a required probability distribution is estimated from the training data. The process is illustrated with a series of experiments and is shown to produce estimates that can improve on those calculated on a small test set.