Determinants of underdiagnosis of COPD in national and international surveys by Lamprecht, B, Soriano, JB, Studnicka, M, Kaiser, B, Vanfleteren, LE, Gnatiuc, L, Burney, P, Miravitlles, M, García-Rio, F, Akbari, K, Ancochea, J, Menezes, AM, Perez-Padilla, R, Montes de Oca, M, Torres-Duque, CA, Caballero, A, González-García, M, Buist, S