Comments on integrating person-centered and variable-centered research on problems associated with the use of alcohol.

For any sample of m different variables obtained on a sample of n different persons, there is an identity transformation between classifications of persons (types) that are defined with person-centered methods and classifications of variables (factors) defined with variable-centered methods: types are manifested in factors and factors are expressed in types. Both kinds of methods analyze the variability-the same variability-in a persons-by-variables data matrix. Person-centered types can be transformed into variable-centered factors. Thus, at a basic level there is a basis for integrating person-centered and variable-centered research. But there are many different ways to implement person-centered methods, just as there are many different ways to resolve variables into factors, and generally any model for analysis directed at identifying types will not be the complement of a model selected for analysis leading to factors. Thus, while the results from the two kinds of analysis can be related to one another, the results they produce in applications can be quite different. Also, in practice, one method is used before the other. For example, person-centered methods might be used to form types, which are then studied with multiple-group, variable-centered methods to test hypotheses specifying invariance or differences of relationships across types. There are good reasons to think in terms of types as one contemplates analysis in terms of variables. But the reverse also is true. In typological analysis, it must be assumed that types exist and that samples of subjects and indicator variables are drawn in ways that can reveal this. Different typologies indicated by person-centered research are most concretely compared if the different studies use comparable sets of persons, indicator variables, and other variables that can indicate correlates. Strictly speaking, none of these sets were comparable in the three substantive studies reviewed here. Nevertheless, at an abstract level it was possible to see that the results of the three studies agreed in indicating that there is a type of adolescent and young adult that, by and large, does not have-or at least does not report having-problems associated with the use of alcohol. This type is in the majority, accounting for approximately 60% of the youth sampled in the reviewed studies. The studies agree also in suggesting that types may emerge along a continuum of maladjustment characterized by increasing use of alcohol and other drugs, failures in school, problems at home, interpersonal difficulties, delinquency, and legal problems. Variable-centered dynamic analyses might further describe phenomena of this kind.