Essay 1 Integrating multiple sources of evidence: a Bayesian perspective

Policies and interventions in the health-care system may have a wide range of effects on multiple patient outcomes and operate through many clinical processes. This presents a challenge for their evaluation, especially when the effect on any one patient is small. In this essay, we explore the nature of the health-care system and discuss how the empirical evidence produced within it relates to the underlying processes governing patient outcomes. We argue for an evidence synthesis framework that first models the underlying phenomena common across different health-care settings and then makes inferences regarding these phenomena from data. Bayesian methods are recommended. We provide the examples of electronic prescribing and increased consultant provision at the weekend.