The ADD/WO and ADDH boys also participated in a placebo-drug crossover study of methylphenidate (Ackerman et al.
In another sample, ADD/WO and ADDH subjects were contrasted on tasks selected to tap either automatic or effortful information processing (Ackerman, Anhalt, Dykman, & Holcomb, 1986a, 1986b).
In our latest and largest ADD sample (Dykman & Ackerman, 1991), we contrasted three subgroups: ADD/WO, ADDH, and ADDH plus aggression (ADDHA).
Three clusters were identified: ADD/WO (N = 49), ADDH (N = 63), and ADDHA (N = 47).
But the boys with ADD/WO had more marked deceleration to the warning signal and greater acceleration to the tones than did the boys with ADDH and ADDHA.
Still, we have used timed tests to little avail; these tests theoretically encourage impulsive responding or attention lapses, which should sort out the ADD/WO and ADDH groups.
OTHER INVESTIGATIONS WITH ADD/WO AND ADDH SUBGROUPS
Studies using both school-based and clinic-referred samples have consistently shown children with ADDH to be rated more adversely on impulsivity and aggressive/defiant symptomatology than children with ADD/WO, whereas the latter children are rated more adversely on internalizing symptomatology such as anxiety, depressed mood, and withdrawal or shyness (Barkley, DuPaul, & McMurray, 1990; Berry, Shaywitz, & Shaywitz, 1985; Cantwell & Baker, 1992; Edelbrock, Costello, & Kessler, 1984; Lahey, Schaughency, Strauss, & Frame, 1984; Shaywitz, Shaywitz, Schnell, & Towie, 1988).
Both ADD/WO and ADDH samples exhibit more difficulties in academic areas than controls, but neither group has been consistently found to have greater problems than the other (Carlson, Lahey, & Neeper, 1986; Lahey et al.