ABSTRACT
Principles of logic in medicine as outlined in Chapter 3 are not important solely for the theory of medicine. Often, we do not realize how much of our reasoning and decisionmaking depends on a solid logical discourse. Let us take an example: As a specialist in community medicine, you notice that cases of meningitis are suddenly unusually frequent in adolescents living in a given urban area. You also know that an effective immunizing agent is available. Hence, you conclude that a vaccination program in the area should be implemented to solve this public health problem. This kind of reasoning and decision can be seen as a syllogism or logical discourse:
Medical practiceLogical discourseEvidence You have received information about new cases of meningitis
Our conclusion will be only as good as the logical postulates that precede it. The best decisions will be based on evidence-based postulates. To know if our postulates are solid, we must know the appropriate criteria of good evidence and be familiar with the methods used to obtain it. In our example, valid evidence of a significant spread of meningitis, Postulate A, will be based on a well-designed occurrence (descriptive) study and surveillance of this disease in the community. We will read about these studies further in the present chapter. Valid evidence of the effectiveness of the vaccine Postulate B will depend on clinical and field trials of the vaccine, which will produce a quantifiable measure of vaccine effectiveness (see Chapter 9). Our choice of vaccination as a preventive measure (Conclusion C) will depend on the results of our decision analysis where competing strategies are taken into account and vaccination emerges as the best possible strategy to control this outbreak.
