There are two kinds of diagnostic models used in psychological research. A categorical model is used most commonly, but dimensional models have also been studied (Skinner, 1979;Strauss, 1973). When developing or using a model, it is important to determine when the model is appropriate for a particular setting. Unfortunately, methods for carrying out this kind of evaluation are only applied infrequently, particularly with categorical models. This paper reviews the importance of evaluating diagnostic models, and empasizes a Bayesian method for evaluating categorical models. An illustration of the method with previously published data is given.S. Atr. J. Psychol. 1982, 12: 61 -64 Daar word twee soorte diagnostiese modelle in psigologiese navorsing gebruik. 'n Kategoriese model word die meeste gebruik, alhoewel dimensionele modelle ook bestudeer is (Skinner, 1979;Strauss, 1973). Wanneer 'n model ontwikkel of gebruik word, is dit belangrik om te bepaal of dit 'n geskikte model is vir die spesifieke situasie en/of omstandighede. Ongelukkig word metodes om hierdie soort evaluering te doen, veral by kategoriese model Ie, seide toegepas. In hierdie artikel word 'n oorsig van die belangrikheid van evaluering van diagnostiese modelle gegee en word 'n Bayesiese metode vir evaluering van kategoriese mode lie beklemtoon. Die metode word ge"illustreer met behulp van reeds gepubliseerde data.