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Item Response Theory Analysis of Lifetime Cannabis-Use Disorder Symptom Severity in an American Indian Community Sample
David A. Gilder, Philip Lau, Cindy L. Ehlers
Objective: The aim of this study was to use Item Response Theory to assess Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised (DSM-III-R), lifetime cannabis-use disorder (CUD) symptom severity and its relationship to first cannabis use before age 15 years, male gender, and childhood conduct disorder in an American Indian community sample. Method: The Semi-Structured Assessment for the Genetics of Alcoholism was used to determine demographic information, age at first use, and DSM-III-R childhood conduct disorder and lifetime CUD symptoms in a community sample of 349 American Indian participants who had used cannabis at least 21 times in a single year. Two-parameter Item Response Theory models generated marginal maximum likelihood estimates for discrimination (a) and threshold (b) parameters for nine DSM-III-R CUD symptoms along an underlying latent CUD severity continuum. Differential Item Functioning (DIF) analysis was used to assess for differences in symptom severity in groups defined by presence versus absence of age at first use before 15 years, male gender, and childhood conduct disorder. Results: CUD symptoms of "use in larger amounts or over longer periods of time," "activities given up," and "role failure" were the most severe symptoms. All CUD symptoms fell on the moderate portion of the severity continuum. "Time spent" was more severe in individuals who first used cannabis after age 15 years, "hazardous use" was more severe in females, and "use in larger amounts or over longer periods of time" was more severe in individuals with co-morbid childhood conduct disorder. Conclusions: Specific risk factors for the development of lifetime CUD are associated with increased severity of several CUD symptoms in this high-risk group. (J. Stud. Alcohol Drugs 70: 839-849, 2009)