Prescribers' beliefs and values as predictors of drug choices.

A cognitive model of the drug-prescribing process, which incorporates prescribers' attitudes (valences) about treatment outcomes and beliefs (instrumentalities) about drug effects, was tested. Twelve physicians were interviewed to identify common outcomes associated with drug therapy; six distinct outcomes were identified. Then 50 family practice residents were given a hypothetical description of a mildly hypertensive patient and three treatment choices. The physicians completed a questionnaire that identified (1) the instrumentalities of each of the alternative treatments for each of the six outcomes and (2) the valences for each outcome. The physicians were also asked to respond to an open-ended question on how they would treat the patient described in the case. Forty-six physicians proposed 39 treatments that corresponded to the three treatments for which instrumentalities and valences were available. The drug-choice model correctly predicted 28 of 39 (72%) therapeutic decisions, which was significantly more than would be expected by chance (p less than 0.01). Both valences and instrumentalities appear important for predicting prescribing intention. Pharmacists can use this model in their attempts to influence prescribing.