1. Department of Evaluation of Innovation and New Technologies; Fundació Clínic per a la Recerca Biomédica; Barcelona 08036; Spain
2. Department of Health Sciences; University of Leicester; Adrian Building, University Road, Leicester LE1 7RH; U.K.
3. Department of Community Based Medicine; University of Bristol; Cotham House, Cotham Hill, Bristol BS6 6JL; U.K.