Using systematic data categorisation to quantify the types of data collected in clinical trials: the DataCat project by Crowley, E, Treweek, S, Banister, K, Breeman, S, Constable, L, Cotton, S, Duncan, A, El Feky, A, Gardner, H, Goodman, K, Lanz, D, McDonald, A, Ogburn, E, Starr, K, Stevens, N, Valente, M, Fernie, G