The validity of a classification or typology can be established in a variety of ways. The approach most frequently emphasized in clinical research is predictive validity, which refers to the ability of a classification scheme to suggest the most likely course and treatment response for a given member of a class. Another approach is construct validity, which refers to the “goodness of fit” between a theoretical construct (e.g., an ideal type of homeless family) and a set of statistical relationships observed empirically. Discriminative validity means that the subgroups classified by a typological theory can be clearly discriminated from one another in terms of major defining characteristics and correlates of homelessness, such as demographic factors, situational variables, service utilization or exogenous factors.
The following is an example of a validation procedure that can be applied to subtypes derived from empirical clustering procedures. Once a satisfactory solution has been achieved: (1) compare the clusters using variables excluded from the original analysis as evidence of discriminant validity; (2) compare clusters on measures of clinical course following a service intervention (predictive validity); (3) examine subtypes in terms of their fit with theoretical constructs of homelessness (construct validity); (4) determine whether there are differential outcomes for subtypes matched to optimal services. Other criteria for evaluating a typology are homogeneity within subgroups, comprehensiveness, simplicity, and practical utility.