1. A computer-implemented defect classification method to classify defects, by using a classifier constructed based on features of defects extracted from detected signals acquired from a defect inspection apparatus, the computer-implemented defect classification method comprising: constructing the classifier by using a classifier construction process commanded by a computer processor to set a branch condition for each of at least one branch point of the classifier, based on instruction of defect classes and feature data previously associated with the defect classes, the branch condition of each branch point including: one or more defect classes located on each side of the at least one branch point, a feature to be used to branch, and a discriminant reference, wherein the classifier construction process includes a priority order specification process configured to display a user selection panel configured to obtain the following data from a user, for each of a plurality of defect classes: a preferred parameter of one of purity and accuracy, a target performance value for said preferred parameter, and a priority ranking in comparison to other defect classes, and wherein the classifier construction process is configured to construct the classifier based on data obtained by the priority order specification process; using the computer processor to input unclassified defects into the classifier, receive classification results from the classifier, and store the classification results and/or exhibit the classification results via a user interface.