1. A method of calibrating a scoring function, the method comprising: accessing a scoring function, wherein the scoring function provides a score indicating a degree to which an input relates to a classification; receiving a first classification; accessing a set of background inputs that have no more than an incidental relation to the first classification; applying the scoring function to each of the background inputs in connection with the first classification so as to create a first distribution of background scores; receiving a first input that is not included in the set of background inputs; altering the scoring function in accordance with the first distribution of background scores to create a first calibrated scoring function; and determining a first calibrated score for the first input in connection with the first classification using the first calibrated scoring function.