In the field of developmental, psychology researchers may have several competing theories with respect to their research subject. In this paper an approach will be proposed that can be used to select the best of these theories. It will be shown that a theory can be translated in a constrained latent class model using inequality constraints. This can be done for several (possibly competing) theories. Subsequently, fit-measures can be used to determine which model (and thus which theory) is supported most by the data. The approach will be introduced using data with respect to self-reported child and adult antisocial behaviour. It will be further illustrated using data obtained using the figural intersection task.Exploratory latent class analysis (ELCA) (Clogg, 1981;Goodman, 1974;Haberman, 1988;Vermunt, 1996) latent classes. In developmental psychology, for example, data with respect to some cognitive ability of children, like responses to items on Piaget's balance scale task, Piaget's water level task or the figural intersection task can be subjected to an ELCA. This can result in groups of children using different strategies (e.g., Boom, Hoijtink, & Kunnen, 2001;Jansen & van der Maas, 1997;Pascual-Leone & Baillargeon, 1994) and the transitions between the groups (Hoben & Hettmansperger, 2001). For a methodological overview and applications see von Eye and Clogg (1994).A key question in ELCA is: into how many homogeneous subgroups should the sample be divided? Usually fit measures (Everitt, 1988;Lin & Dayton, 1997) are used to determine which number of classes is optimal. Furthermore, the resulting classes have to be interpreted. To illustrate this, consider an ELCA of the responses of 2001 women to several items with respect to self-reported child and adult antisocial behaviours. In order to assess maternal antisocial disorder, the mothers were asked about five childhood antisocial behaviours and four adult behaviours. In Table 1 the items (responses to either ''yes'' or ''no'' questions) and the response percentages can be found. The women were mothers of 5-month-old infants 2 LAUDY ET AL.from a population-based longitudinal study of the development of children of the province of Quebec, Canada (Jette, Desrosiers, Tremblay & Thibault, 2000;Zoccolillo, 2000).In the top panel of Table 2, three fit measures for exploratory analyses with two, three, and four classes are displayed. Hoijtink (1998Hoijtink ( , 2001 developed these fit measures to be able to select the best of a number of exploratory and confirmatory (see below) latent class models. The first measure is 72 log of the marginal likelihood (Kass & Raftery, 1995). This measure can be seen as the Bayesian counterpart to information criteria like AIC, CAIC and BIC (Kass & Raftery, 1995). It is a relative (with respect to the corresponding numbers for other models) fit measure: the smaller the number the better the model. If, a priori, each model is considered to be equally good, 72 log of the marginal likelihood can be transformed to posterior probabilities ...