Artificial neural networks (ANNs) are computer-based algorithms capable of pattern recognition particularly suited to making diagnoses. ANNs do not require explicit encoding of process knowledge in a set of rules and can be trained from examples to recognize and categorize complex patterns. ANNs learn more efficiently when the data to be input into the neural network is preprocessed. Various ANN approaches to the analysis of data have seen extensive application to biomedical problems, including those in the areas of diagnosis and drug development. Unsupervised neural networks are also extensively used for the analysis of DNA microarray data.