title: The Gini coefficient as a measure for understanding accrual inequalities in multicenter clinical studies.
abstract: OBJECTIVE
  Clinical sites participating in multicenter trials may have unequal performance in recruiting subjects. We propose using the Gini coefficient as a quantitative measure of site accrual inequalities.
  
  
  METHODS
  We evaluated the relationship of this metric to other study characteristics across 166 clinical studies (27,865 subjects) conducted by the AIDS Clinical Trials Group between 1986 and 1999.
  
  
  RESULTS
  Overall there was a modest recruitment inequality among clinical centers (mean Gini=0.33). In multivariate modeling, site accrual inequalities were higher when there was more protracted enrollment, and a larger number of sites and were lower in antiretroviral studies than other studies. In long-term studies, the site accrual inequality increased significantly over time (P=0.004). In efficacy trials, a higher Gini coefficient was associated with higher likelihood of the study results being statistically significant (P=0.010).
  
  
  CONCLUSIONS
  The Gini coefficient may be easily and routinely incorporated in the description of the characteristics of a clinical study and may provide insights about its enrollment pattern.
authors.affiliation: Clinical Trials and Evidence-Based Medicine Unit, Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina 45110, Greece.
authors.forename: Anna-Bettina
authors.initials: AB
authors.lastname: Haidich
authors.forename: John P A
authors.initials: JP
authors.lastname: Ioannidis
mesh_terms: D000328:Adult; D002986:Clinical Trials as Topic / Q000379:methods*; D015658:HIV Infections / Q000628:therapy; D006801:Humans; D016015:Logistic Models; D015337:Multicenter Studies as Topic / Q000379:methods*; D018579:Patient Selection; D016032:Randomized Controlled Trials as Topic / Q000379:methods; D012107:Research Design