it is generally agreed that structure, meaning the way a health system is set up ,has an important bearing on how persons in that system behave and, consequently, on the quality of care offered and enjoyed. In some ways, structure could be the major determinant of the quality of care that the system, on the average , is able to offer, But detailed variations in many system characteristics have a rather weak relationship to corresponding variations in quality. Therefore, variations in system characteristics, unless they are unusually large, yield only presumptive judgments on the quality of care