Chunk #11 — Some general methodological considerations — Selection of symptoms or questionnaire items — Item content: severity

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Does nature have joints worth carving? A discussion of taxometrics, model-based clustering and latent variable mixture modeling.

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To illustrate, suppose a disorder is in fact continuous in a general population. If we select symptom indicators only at the high end of the continuum (see Fig. 2a), then the majority of subjects are likely not to endorse any of the items. As a result, these subjects are lumped into a single group, and individual differences within that group are masked. The subjects on the high end of the continuum would be most likely to endorse all items, thus also forming a group that has negligible within-group differences. The grouping of the subjects in this example would be artificially induced by the item selection, and not represent the true nature of the latent construct.