1. A method for locating an arrhythmogenic focus in a heart of a living subject, comprising the steps of: obtaining training electrical signal data from respective training locations of a training set of hearts; automatically analyzing said training electrical signal data to identify training complex fractionated electrograms therein; recording determinations of medical significance of a plurality of observers with respect to said training complex fractionated electrograms; generating first estimations of medical significance at said respective training locations by fitting a mixed regression model to said training complex fractionated electrograms and said determinations of medical significance; obtaining patient electrical signal data from respective locations of a patient heart; automatically analyzing said patient electrical signal data to identify patient complex fractionated electrograms in said patient heart; applying said mixed regression model to said patient complex fractionated electrograms to obtain second estimations of medical significance at said respective locations of said patient heart; and displaying an indication that one or more of said respective locations of said patient heart are medically significant.