“…The effectiveness of the treatment programme depends on the patient’s individual characteristics at admission and on the treatment process itself [ 17 , 20 , 27 , 28 ]. In most studies, the best predictor of the effectiveness of TCs is the length of stay (treatment retention) [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ], mainly because a longer stay implies that the patients will receive more therapeutic interventions, which may increase the likelihood of positive change [ 28 , 39 , 40 ]. Numerous studies have found that the minimum length of stay needed to obtain clinically relevant results is approximately three months [ 34 , 37 , 41 , 42 , 43 , 44 , 45 , 46 ].…”