SYSTEM Research note on: Using formal logic for illustrating coherence of systematic review evidence

CONTEXT: Clinical knowledge, as any other type of knowledge, can be regarded as justified belief. The justification of belief follows two cognitive strategies: coherence of logic and correspondence of facts.

PROBLEM: Coherence strategy has been traditionally favoured in the justification of beliefs concerning medical interventions throughout the centuries and is today still preferred by many clinicians as providing “logical sense” for or against the application of therapies, diagnostics or preventive measures. The use of correspondence strategy has only recently being emphasized within the medical field as evidence-based medicine (EBM). There is a risk that evidence from EBM, i.e. as appraised through systematic reviews, concerning clinical questions is ignored by clinicians, if no deeper logical integration of such evidence through coherence strategy is given.

SUGGESTED SOLUTION: In order to explore how coherence strategy in regard to systematic review evidence may be applied, basic principles of formal logic were used on an example concerning systematic review evidence regarding the assumed active anticaries effect of xylitol. The example shows how a coherent Web-of-Beliefs (WoB) may be structured that way and how systematic review evidence may in turn serve as empirical support for such a coherent web-of-beliefs. The presented example also shows how strict logical coherence alone can be no guarantee for correctness of beliefs concerning medical interventions.