This paper is an argument, not a new study. The author makes the case that emotional impulsiveness, and the trouble managing emotion that follows from it, should be treated as a core part of ADHD rather than a merely associated feature. He builds this from the history of the disorder and from studies done elsewhere, not from data he collected himself.
The studies he points to looked at different groups. One followed hyperactive children in Milwaukee into adulthood. Another compared adults who had ADHD with both clinical and community control groups. A third was a survey used to set norms for a rating scale, covering 1,249 adults ages 18 to 81. Across this work he reports that emotional impulsiveness showed up more in the ADHD groups than in the control groups, was about as common as the standard inattention and hyperactive-impulsive symptoms, and helped predict impairment beyond those two usual dimensions. In children with the combined type of ADHD, he notes these emotional symptoms make up three to four of the eight symptoms on the oppositional defiant disorder list.
The author is careful about the limits. He says far less is known about the emotion-regulation side than about impulsiveness itself, that the evidence is limited, and that several of the studies he leans on were still in press.
Source: Barkley R. Why Emotional Impulsiveness Should Be a Central Feature of ADHD. The ADHD Report (2010). doi:10.1521/adhd.2010.18.4.1