[Costs, costs and more costs: which one should we use?].

A cost is not an intrinsic feature of a product in the same way as temperature is for water and air. It is a calculation based on theory and convention. Costs may be characterised by their object (an hospital admission, a hospitalization day, a diagnostic related group, a treatment phase), their contents (costs directly attributable to the patient, controllable costs, including not only departmental operating costs but also costs resulting from the department's activity, full costs including administrative and infrastructure overhead costs), the point of reference from where the costs are considered (from the point of view of the family, the health professionals suppliers, the buyers, the health care system, or society) and the time when the costs were calculated. The cost framework which must be considered in any economic evaluation must relate to the budgetary concerns of the party whose involvement is sought in a health care project. There is no all encompassing study in this field; an evaluation performed for one type of contributor must only consider this party's point of view.