title: Further validation of a marijuana purchase task.
abstract: BACKGROUND
  A valid measure of the relative economic value of marijuana is needed to characterize individual variation in the drug's reinforcing value and inform evolving national marijuana policy. Relative drug value (demand) can be measured via purchase tasks, and demand for alcohol and cigarettes has been associated with craving, dependence, and treatment response. This study examined marijuana demand with a marijuana purchase task (MPT).
  
  
  METHODS
  The 22-item self-report MPT was administered to 99 frequent marijuana users (37.4% female, 71.5% marijuana use days, 15.2% cannabis dependent).
  
  
  RESULTS
  Pearson correlations indicated a negative relationship between intensity (free consumption) and age of initiation of regular use (r=-0.34, p<0.001), and positive associations with use days (r=0.26, p<0.05) and subjective craving (r=0.43, p<0.001). Omax (maximum expenditure) was positively associated with use days (r=0.29, p<0.01) and subjective craving (r=0.27, p<0.01). Income was not associated with demand. An exponential demand model provided an excellent fit to the data across users (R(2)=0.99). Group comparisons based on presence or absence of DSM-IV cannabis dependence symptoms revealed that users with any dependence symptoms showed significantly higher intensity of demand and more inelastic demand, reflecting greater insensitivity to price increases.
  
  
  CONCLUSIONS
  These results provide support for construct validity of the MPT, indicating its sensitivity to marijuana demand as a function of increasing cost, and its ability to differentiate between users with and without dependence symptoms. The MPT may denote abuse liability and is a valuable addition to the behavioral economic literature. Potential applications to marijuana pricing and tax policy are discussed.
authors.affiliation: Center for Alcohol and Addiction Studies, Brown University School of Public Health, Box G-S121-4, Providence, RI, 02912, USA. Electronic address: Elizabeth_Aston@Brown.edu.
authors.forename: Elizabeth R
authors.initials: ER
authors.lastname: Aston
authors.affiliation: Providence Veterans Affairs Medical Center, Providence, RI, 02908, USA; Center for Alcohol and Addiction Studies, Brown University School of Public Health, Box G-S121-4, Providence, RI, 02912, USA.
authors.forename: Jane
authors.initials: J
authors.lastname: Metrik
authors.affiliation: Department of Psychiatry and Behavioural Neurosciences, McMaster University, Hamilton, Ontario, L8N 3K7, Canada; Center for Alcohol and Addiction Studies, Brown University School of Public Health, Box G-S121-4, Providence, RI, 02912, USA.
authors.forename: James
authors.initials: J
authors.lastname: MacKillop
mesh_terms: D000067290:Behavior Rating Scale; D003132:Commerce / Q000191:economics*; D003365:Costs and Cost Analysis; D066249:Craving; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000175:diagnosis / Q000191:economics*; D008385:Marijuana Smoking / Q000191:economics*; D012054:Reinforcement, Psychology; D057566:Self Report
keywords: Behavioral economics; Cannabis dependence; Demand curve; Marijuana; Purchase task