1. A method of identifying an aberrant feature on a nucleic acid array, comprising: a) obtaining a log transformed normalized value indicating the amount of hybridization of a test sample to a first feature on said nucleic acid array; b) calculating a z-score for said first feature using: i. said log transformed normalized value; and ii. the distribution of reference log transformed normalized values that indicate the amount of hybridization of control samples to the corresponding feature on a plurality of reference arrays; and c) identifying said test feature as aberrant if it has a z-score that is above or below a defined threshold.