He received a doctoral degree in Statistics from the University of Oviedo (north of Spain). He has worked on different topics including kernel density estimators, k-sample problems, and survival analysis. Currently, he focusses on diagnostic/prognosis problems and on instrumental variables procedures on Cox regression models. His works have been published in prestigious journals including Statistical Methods in Medical Research, Biostatistics, New England Journal of Medicine and Lancet, with more than 150 papers published in peer review journals. In addition, he acts as reviewer in a number of methodological and medical journals including The Lancet.