A pragmatic basis for judging models and theories in health psychology: the axiomatic method.

Psychology and its subfield of health psychology suffer from a lack of standardized terminology and a unified theoretical framework for the prediction and explanation of health behaviour. Hence, it is difficult to establish whether a given theory is logically consistent and to compare different theories. Science involves both empirical and conceptual issues. It is asserted that psychology has overemphasized the former and underemphasized the latter. Empirical psychology needs an explicit, shared conceptual system in order to develop its theories. An example of an axiomatic method (Psycho-Logic; see e.g. J. Smedslund.Psychological Inquiry 1991a; 2: 325-338) is applied to show how the Health Belief Model,the Theory of Planned Behaviour and Social Cognitive Theory all conform to the a priori conditions of acting. One implication is that studies of the predictive power of theories stated as definitional truths only assess auxiliary hypotheses, i.e. the extent to which the measuring instruments are reliable and valid. On the other hand, the introduction of logic into health psychology can facilitate genuine empirical studies by helping to avoid so-called 'pseudoempirical' work (Smedslund, J. In Smith, Harré & Van Langenhove (Eds.) Rethinking psychology, 1995). Systems such as Psycho-Logic can also enhance conceptual integration by using logic to explicate and demonstrate intuitive relations. Implications for practitioners are discussed briefly.