Evidence-based health care is the conscientious use of current best evidence in making decisions about the care of individual patients or the delivery of health services.
Current best evidence is up-to-date information from relevant, valid research about the effects of different forms of health care, the potential for harm from exposure to particular agents, the accuracy of diagnostic tests, and the predictive power of prognostic factors.
Evidence-based healthcare "takes place when decisions that affect the care of patients are taken with due weight accorded to all valid, relevant information".
World Health Organization. European Observatory on Health Systems and Policies. Glossary. 2009.
The evidence base refers to a body of information, drawn from routine statistical analyses, published studies and “grey” literature, which tells us something about what is already known about factors affecting health.