Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. calza@med.unibs.it|Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. calza@med.unibs.it|Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. calza@med.unibs.it