Cost and outcome of behavioural activation versus cognitive behaviour therapy for depression (COBRA): study protocol for a randomised controlled trial. by Rhodes, S, Richards, D, Ekers, D, McMillan, D, Byford, S, Farrand, P, Gilbody, S, Hollon, S, Kuyken, W, Martell, C, O'Mahen, H, O'Neill, E, Reed, N, Taylor, R, Watkins, E, Wright, K