1. A method of targeting particular service users, wherein characteristics of the users are represented in a plurality of records of a data set, the method comprising: identifying records of the data set representing users who have exhibited particular desirable characteristics, based on supervised classification processing; based on identification of the records, processing the records of the data set to indicate a bias for application in unsupervised clustering processing; and clustering the records, processed to indicate a bias, using the unsupervised clustering process, including determining a particular clustering among alternate possible clusterings of the records of the data set; and targeting particular service users based on the result of the clustering step.