Impairment of health-related quality of life in patients with inflammatory bowel disease: a Spanish multicenter study - Casellas, F; Arenas, J I; Baudet, J S; Fabregas, S; Garcia, N; Gelabert, J; Medina, C; Ochotorena, I; Papo, M; Rodrigo, L; Malagelada, J R (Inflamm Bowel Dis, 2005)