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Fuzzy logic could well be a description of what goes on in many a doctor's brain when the telephone rings at three in the morning but, more formally, it is a mathematical system introduced in 1965 which deals with imprecision, uncertainty, and partial truth. Since all of these attributes are part of the staple fare of medical practice most doctors would no doubt want to buy into such a system. In São Paulo, Brazil it was used to arrive at a successful measles mass vaccination strategy when they had a limited number of doses of vaccine available (Eduardo Massad and colleagues. International Journal of Epidemiology1999;28:550–7).
The fuzzy logic system of decision making requires a set of goals, a set of possible actions, and a set of constraints, from which a decision can be made about the action that best satisfies the goals and constraints. The team in Brazil were faced with a rise in measles notifications despite a previously successful vaccination programme. They took as their goal the control of measles in children under 14 and considered 8 possible vaccination strategies. They obtained a series of constraints from an expert medical panel. Using fuzzy logic one strategy was chosen: selective vaccination of children aged 9 months to 6 years at fixed sites in the primary care network. The strategy proved successful in São Paulo city but a second mass vaccination campaign in the interior of the state was necessary 2 months later.