This book is for users of comparisons in health care and for researchers. More clinicians managers and patient groups are using research to make comparisons. Information technology and new databases make comparisons easier but not necessarily better. Comparisons can help us discover the causes of disease whether a treatment is effective if it is worth the cost whether a service is performing badly and the value of a health reform or policy. Comparisons can help us learn from other cultures and understand the implications for our own health services. Yet it is all too easy to misinterpret or uncritically accept a study and reach invalid conclusions. This book encourages decision-makers to make more use of comparative research but with an awareness of the limitations of comparisons. Its practical approach enables researchers to plan and carry out better comparative research and to develop new methodologies for this fast growing field of research.