“…In the studies on DRA included in this review, preferred foods or drinks were always used as positive reinforcers, either alone or in combination with social praise (Brown, Spencer, & Swift, 2002;Cooper et al, 1999;Levin & Carr, 2001;Riordan, Iwata, Wohl, & Finney, 1980;Riordan, Iwata, Finney, Wohl, & Stanley, 1984). Thus, the effectiveness of stimuli other than preferred foods or drink remains unclear.…”