title: Impact of placebo assignment in clinical trials of tic disorders.
abstract: BACKGROUND
  Understanding the impact of placebo treatment is pivotal to the correct interpretation of clinical trials. The aim of present study was to examine the placebo effect in tic disorders.
  
  
  METHODS
  Raw data were obtained for 6 placebo-controlled parallel and cross-over trials that involved medical interventions for tic disorders. Tic severity was measured using the Yale Global Tic Severity Scale. Placebo effect was defined as an improvement of at least 30% over baseline scores in the total tic score and was considered clinically relevant when at least 10% of patients in the placebo-arm met that benchmark.
  
  
  RESULTS
  In total, 91 placebo-treated patients (80% males; mean age, 16.5 years; standard deviation, 10.5 years) were included. Although there was a trend toward improvement in the total tic scores after placebo administration (P=0.057), the magnitude of the placebo effect was small (Cohen's d=0.16) but relevant (19% of the sample). Females were more likely than males to have a placebo effect.
  
  
  CONCLUSIONS
  The magnitude of the placebo effect in tic disorders appeared to be small. Further longitudinal studies using objective assessments for tic disorders are warranted to confirm the current results. © 2013 Movement Disorder Society.
authors: Neurology Department, Complejo Asistencial Universitario of Burgos, Burgos, Spain.
authors: Esther
authors: E
authors: Cubo
authors: Miguel
authors: M
authors: González
authors: Harvey
authors: H
authors: Singer
authors: E Mark
authors: EM
authors: Mahone
authors: Lawrence
authors: L
authors: Scahill
authors: Kirsten R
authors: KR
authors: Müller-Vahl
authors: Raul
authors: R
authors: de la Fuente-Fernández
authors: Diana
authors: D
authors: Armesto
authors: Katie
authors: K
authors: Kompoliti
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D018592:Cross-Over Studies; D016206:Databases, Bibliographic / Q000706:statistics & numerical data; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015990:Placebo Effect; D016032:Randomized Controlled Trials as Topic; D013981:Tic Disorders / Q000188:drug therapy*; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult
keywords: Tourette syndrome; clinical trials; movement disorders; placebo; tics