Using natural experiments to evaluate population health and health system interventions: new framework for producers and users of evidence.

Natural experiments are widely used to evaluate the impacts on health of changes in policies, infrastructure, and services. The UK Medical Research Council (MRC) and National Institute for Health and Care Research (NIHR) have published a new framework for conducting and using evidence from natural experimental evaluations. The framework defines key concepts and describes recent advances in designing and planning evaluations of natural experiments, including the relevance of a systems perspective, mixed methods, and stakeholder involvement. It provides an overview of the strengths, weaknesses, applicability, and limitations of the range of methods now available, and makes good practice recommendations for researchers, funders, publishers, and users of evidence.