title: The effect of parity-induced copayment reductions on adolescent utilization of substance use services.
abstract: OBJECTIVE
  The purpose of this study was to determine if the reduction in copayment amount by a large self-insured state employer increased utilization of adolescent services. Specifically, the study sought to discover if the number of unique adolescent users of substance use outpatient services increased as a result of reductions in cost-sharing arrangements.
  
  
  METHODS
  The data utilized in this study were 31,585 records from administrative claims data on utilization of mental health and substance abuse services from members of a state indemnity plan fromJuly 1998 through December 2001, translating to 36 months of pre-intervention data and 6 months of postintervention data. Monthly longitudinal data before and after benefit design change were analyzed using a quasi-experimental time series design, using Box and Jenkins' autoregressive, integrated, moving-average time-series modeling methods. The primary outcome measure was the number of unique users of services.
  
  
  RESULTS
  The hypothesis that service utilization would increase following the implementation of a reduction in copayment amount (the intervention) was supported in these analyses for adolescents' substance use service utilization. A significant increase in the number of unique adolescent users of substance use services was detected in the month following the intervention (p < .01).
  
  
  CONCLUSIONS
  The results of this study suggest that a reduction in adolescents' substance use service copayment requirements to a level equal to those for general medical services may be a step toward assuring full parity between such types of services. These findings provide potentially important information regarding the possible effects of broader policy changes, as parity in benefit design is a common component of laws that attempt to ensure "full parity."
authors.affiliation: Health Services and Policy Analysis, School of Public Health, University of California, Berkeley, Berkeley, California, USA. elc28@uclink.berkeley.edu
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: Ciemins
mesh_terms: D000293:Adolescent; D002648:Child; D016001:Confidence Intervals; D017047:Cost Sharing / Q000191:economics* / Q000706:statistics & numerical data; D006801:Humans; D007349:Insurance, Health, Reimbursement / Q000191:economics* / Q000706:statistics & numerical data; D016320:Substance Abuse Treatment Centers / Q000191:economics* / Q000706:statistics & numerical data*; D019966:Substance-Related Disorders / Q000191:economics* / Q000628:therapy