The construct and measurement equivalence of cocaine and opioid dependences: A National Drug Abuse Treatment Clinical Trials Network (CTN) study.

Although DSM-IV criteria are widely used in making diagnoses of substance use disorders, gaps exist regarding diagnosis classification, use of dependence criteria, and effects of measurement bias on diagnosis assessment. In this study, the authors examined the construct and measurement equivalence of diagnostic criteria for cocaine and opioid dependences, including whether each criterion maps onto the dependence construct, how well each criterion performs, how much information each contributes to a diagnosis, and whether symptom-endorsing is equivalent between demographic groups. Item response theory (IRT) and multiple indicators-multiple causes (MIMIC) modeling were performed on data from public-use files from a sample of stimulant-using methadone maintenance patients enrolled in protocol CTN-0007 of the Clinical Trials Network (“Motivational Incentives for Enhanced Drug Abuse Recovery: Methadone Clinics”). IRT modeling showed that symptoms of cocaine and opioid dependences, respectively, were arrayed along a continuum of severity. All symptoms had moderate to high discrimination in distinguishing drug users between severity levels. “Withdrawal” identified the most severe symptom of the cocaine dependence continuum. MIMIC modeling revealed some support for measurement equivalence. Study results indicate that dependence on cocaine or opioids represents a unidimensional continuum of risk. “Withdrawal” measures the most severe symptom of the cocaine dependence construct and is less likely to be exhibited by cocaine users. On the other hand, “withdrawal” and “tolerance” appear to indicate lower severity levels of the opioid dependence construct. Overall, this study suggests that self-reported clinical symptoms of cocaine and opioid dependences and their underlying constructs can be measured appropriately among treatment-seeking polysubstance users.

Supported by the Duke Clinical Research Institute (CTN DSC 1).

Related protocols: CTN-0007