[Studies of cost-effectiveness and cost-usefulness in radiology]

In the current context of significant increase of health care costs over the last decades, and in a system of global budget for health care, the concept of cost-effectiveness is one of the leading elements in the political decision making process for a given strategy. Therefore, it is important for the physician to be able to understand and critically interpret cost-effectiveness and cost-utility analyses. This article tries to illustrate comprehensively some of their key concepts. The perspective and the time horizon of the study should be clearly specified. The cost-effectiveness ratio is a synthetic summary based on a micro-costing approach in order to determine the true costs (numerator), and on an effectiveness (utility) assessment which should take into account the preferences of the community (denominator) in order to allow comparisons between interventions of different natures. Advances in the development of decision analysis softwares and in the standardization of the methodology of these studies have yielded considerable improvement in the reliability of their results. Several persisting methodological problems are the scope of current research, such as the discounting rate and the calculation of the minimal sample size required to reach a statistically significant threshold.