A third possibility is that there are discrete classes of individuals and that within each class there is a dimensional trait that allows for within-class degrees of severity. This combination of classes and dimensions has only recently been examined through factor mixture models (otherwise known as hybrid models). The fit of these models can be compared with the fit of dimensional and latent class models using fit indices such as likelihood-based tests or information criteria [27, 28]. Such an approach has been used with alcohol, tobacco, and performance and image enhancing drugs (PIEDs). These studies have found that the factor mixture models provided the best fit when compared to dimensional and categorical models [29-32].
