1. Pain Treatment Unit, Doña Mercedes Primary Health Care Centre, Andalusian Public Health System, Dos Hermanas, Spain
2. Carlos III Health Institute, Network of Research in Health Services in Chronic Diseases (REDISSEC), Madrid, Spain
3. San Andrés Torcal Primary Health Care Centre, Andalusian Public Health System, Malaga, Spain
4. Registre de Càncer, Servei d'Epidemiologia, Direcció General de Salut Pública, Palma, Spain
5. El Lugar Primary Health Care Centre, Andalusian Public Health System, Chiclana de la Frontera, Spain
6. Support Research Unit, Andalusian Public Health System, Costa del Sol Hospital, Marbella, Spain
7. Doña Mercedes Primary Health Care Centre, Andalusian Public Health System, Dos Hermanas, Spain