title: The Prevalence of Tic Disorders and Clinical Characteristics in Children.
abstract: BACKGROUND
  Prevalence is a simple statement about the frequency of a disease in the population. For many medical conditions, including Tourette syndrome, there are true cases that have not been previously diagnosed due to problems of access to appropriate clinical services. Therefore, to obtain a trustworthy estimate of prevalence, it is necessary to go beyond cases identified in clinical settings and evaluate community samples.
  
  
  METHODS
  We reviewed 11 community surveys in children with Tourette syndrome (TS) published since 2000. We also examined the frequency of co-occurring psychiatric conditions in community samples and large clinically-ascertained samples.
  
  
  RESULTS
  Transient tics are relatively common affecting as many as 20% of school-age children. The 11 studies reviewed here offer a wide range of estimates from 2.6 to 38 per 1000 children for TS. Six studies provide estimates in a narrower range from 4.3 to 7.6 per 1000, but the confidence interval around this narrower range remains wide. Six studies provided results on chronic tic disorders ranging from 3 to 50 per 1000 for Chronic Motor Tic Disorder and 2.5 to 9.4 per 1000 for Chronic Vocal Tic Disorder. Community samples and large clinically-ascertained samples consistently show high rates of ADHD, disruptive behavior and anxiety disorders in children with TS.
  
  
  CONCLUSIONS
  The wide range of prevalence estimates for TS and chronic tic disorders is likely due to differences in sample size and assessment methods. The best estimate of prevalence for TS in school-age children is likely to fall between 4 and 8 cases per 1000. Clinical assessment of children with chronic tic disorders warrants examination of other problems such as ADHD, disruptive behavior and anxiety.
authors.affiliation: Emory School of Medicine, Marcus Autism Center, Atlanta, GA.
authors.forename: Lawrence
authors.initials: L
authors.lastname: Scahill
authors.affiliation: Johns Hopkins School of Medicine, Baltimore, MD.
authors.forename: Matthew
authors.initials: M
authors.lastname: Specht
authors.affiliation: Emory School of Medicine, Marcus Autism Center, Atlanta, GA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Page