Protocol of a multicentric prospective cohort study for the VALIDation of the IBD-disk instrument for assessing disability in inflammatory bowel diseases: the VALIDate study oleh C. Le Berre, A. Bourreille, M. Flamant, G. Bouguen, L. Siproudhis, M. Dewitte, N. Dib, E. Cesbron-Metivier, T. Goronflot, M. Hanf, P.-A. Gourraud, E. Kerdreux, A. Poinas, C. Trang-Poisson