7. The method of claim 6 wherein at least a first one of the attributes has a respective first range of values including at least three possible values.
6. A method of training at least a first machine learning system of a candidate selection system, the method comprising: identifying by at least one processor a first entity and a second entity, out of a plurality of entities, that are a historically successful pairing; generating by the at least one processor a plurality of hypothetical entities, each of the hypothetical entities based on the second entity in the historically successful pairing, and each of the hypothetical entities having a plurality of attributes which are based on a corresponding plurality of attributes for the second entity upon which the hypothetical entity is based, at least one attribute of the plurality of attributes of the hypothetical entity modified to be different from the corresponding attribute of the second entity in the historically successful pairing; generating by the at least one processor a plurality of hypothetical alternative pairings, each of the plurality of hypothetical alternative pairings comprising: an alternative pairing between the first entity and one of the plurality of hypothetical entities based on the second entity; providing the first machine learning system of the candidate selection system with the historically successful match as one training example; and providing the first machine learning system of the candidate selection system with at least one of the hypothetical alternative pairings as an additional training example.