 Swerdlow highlights the importance of studies in new areas such as behavioral techniques, and says that "the whole-cloth dismissal of psychologic forces in the pathobiology of TS was a strategic error".Questions remain about whether co-occurring (comorbid) conditions should be part of the core definition, and why sensory phenomena, which are a core part of Tourette's, are not part of the diagnostic criteria.Dropping the criteria for impairment from the diagnosis resulted in higher estimates of the prevalence of TS (the question of "who has it?