Distinguishing Categories from Continua

Psychologists are interested in knowing whether psychological constructs are categorically or continuously distributed in the population, as the two types of models have distinct implications for the etiology, diagnosis, and treatment of mental disorders. Categorical models are based on the assumption that differences between normal and abnormal psychological functioning are qualitative; that is, symptoms of psychopathology are distinct and differentiable from normative psychological phenomena. Dimensional models, on the other hand, describe differences between normal and abnormal psychological phenomena as quantitative. In continuous models, clinically significant symptoms represent the extremes of traits that are present in every individual to some extent. Methods frequently used to discriminate between categorical and continuous models of psychopathology include cluster analysis, taxometrics, and latent variable modeling. However, no method is foolproof. It is also important to consider how continuous and categorical models differ in terms of their reliability and validity. Continuous measures are generally more reliable than categorical measures.