Classification is the systematic assignment of entities to homogeneous categories, groups, or types according to specified rules or parameters. By formulating classification systems for crimes, criminals, and patterns of criminal behavior, criminologists hope to increase their understanding of these phenomena. Taxonomies are comprehensive [Page 119]systems that seek to categorize a broad array of phenomena. Syndromes are narrower in scope. Categories can be formulated heuristically on the basis of psychological or criminological theory or empirically on the basis of observations. Any shared characteristic can serve as the basis for a classification system as long as those assigned to each category have more in common with each other than those placed in other groups. Successful systems are valid, are reliable, and make a contribution to knowledge, as ...