The Evaluation of Verbal Models

A verbal model is a model that allows for linguistic rather than numerical variables, and for causal relationships between the variables to be formulated verbally rather than mathematically (Wenst0p, 1976). Examples for such include Kickert's model (1979) in which Mulder's theory of power is reformalized verbally, Wenst0p's (1976) deductive verbal models of organizations, and Yager's (1979; 1984), Kwakernaak's (1978; 1979), and Zadeh's (1968; 1981) models of fuzzy probabilities (Zwick & Wallsten, 1989). A fundamental issue in the theory of modelling is validation of a model. In the conventional modelling exercise this rarely consists of more than the calculation of some accuracy measure between the model and the data. However, with verbal models this approach encounters several difficulties. Several authors (Wenst0p, 1975; Yager, 1978; Tong, 1980) have discussed methods for comparing linguistic values--empirical and predicted--for validation purposes. However, these techniques suffer from several problems that will be discussed next.