A method for evaluating the relationship between the cost and the effectiveness of an activity or to compare similar or alternative activities to determine the relative degree to which they will produce the desired objectives or outcomes. The degree of effectiveness is understood to be the extent to which a given activity or programme contributes to attaining the objectives of reducing the dimension of a problem or improving an unsatisfactory situation. The preferred action is the one that requires the least cost to produce a given level of effectiveness. In the health care field, the cost is expressed in monetary terms but the consequences may be expressed in physical units such as healthy life-years gained, the number of cases of disease detected or the improvement in health status of a population.