A method for determining accuracy of a classifier which provides an indication of the degree of correctness of the classifier rather than a mere correct/incorrect indication. The accuracy of the classifier is determined by determining a set of categories of an arrangement of categories selected for an item by the classifier and determining a set of categories of the arrangement selected for the item by an authoritative classifier. An accuracy measure which indicates a degree of correctness of the classifier is then determined based on the categories selected by the classifier and the categories selected by the authoritative classifier.