1 Preventive Medicine and Public Health Training Unit, Parc de Salut Mar, Universitat Pompeu Fabra, Agència de Salut Pública de Barcelona, Spain Institute of Environmental Assessment and Water Research, Spanish Council for Scientific Research, Barcelona, Spain, aurelio.tobias@idaea.csic.es GREMPAL Research Group, Idiap Jordi Gol and CIBERFes, Universitat Autonoma de Barcelona and Instituto de Salud Carlos III, Barcelona, Spain Centre for Statistics in Medicine, Botnar Research Centre, NDORMS, University of Oxford, United Kingdom.