Unrelated medical care in life years gained and the cost utility of primary prevention: in search of a ‘perfect’ cost–utility ratio

An important subject of debate in cost–utility analysis of health care programmes is whether to include costs of unrelated medical care in life years gained. The inclusion of such costs is likely to be of consequence in the case of primary prevention. This paper presents different strategies regarding the inclusion not only of the costs, but also of the health effects of unrelated medical care in economic evaluations. Four different cost–utility ratios are presented and related to the criterion of internal consistency. In addition, the possibility to relate the ratios to a well‐posed decision problem is analysed. An example computes the different ratios for smoking cessation interventions in different age groups. Including health care costs of unrelated medical care in life years gained increases cost utility ratios, but excluding unrelated medical costs favours smoking cessation interventions targeted at older smokers over those at younger smokers. We conclude that for primary prevention only a cost utility ratio that includes both the costs and effects of unrelated medical care meets the criterion of internal consistency and is related to a meaningful decision problem. Therefore, this type of cost–utility ratio should be preferred even if the data requirements may be substantial. Copyright © 2006 John Wiley & Sons, Ltd.