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Funding This work was partially supported by RETICS Program, RD08/0075 (RIER) from Instituto de Salud Carlos III (ISCIII), within the VI PN de I+D+i 2008–2011 (FEDER). L-MD-G was supported by the ‘Ayudas Predoctorales de Formación en Investigación en Salud (PFIS—FI09/00544)’ from the ‘Instituto de Salud Carlos III’.
Competing interests None.
Ethics approval The study was approved by the local ethical committees of all participating centres.
Provenance and peer review Not commissioned; externally peer reviewed.
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