Quantifying cannabis use with the timeline followback approach: a psychometric evaluation

Area of Science:

• Cannabis research
• Substance use measurement
• Psychometrics

Background:

• Accurate quantification of cannabis use is challenging due to the lack of standardized units.
• Self-report instruments often prove inadequate for precise cannabis use measurement.
• This study explores the feasibility of a cannabis substitute for reliable and valid quantity assessment.

Purpose of the Study:

• To assess the reliability and validity of using Marijuanilla, a cannabis substitute, for quantifying cannabis use.
• To determine if Marijuanilla can improve the accuracy of self-reported cannabis consumption.
• To evaluate the potential of Marijuanilla in clinical and epidemiological cannabis research.

Main Methods:

• A 90-day Timeline Followback interview was conducted with 98 adult Australian cannabis users.
• Participants used Marijuanilla to report the quantity of cannabis consumed.
• Interviews were repeated for reliability testing, and collateral reports were obtained for validation.

Main Results:

• Excellent inter-rater and good to excellent test-retest reliability were observed.
• Participant and collateral reports showed unacceptable intra-class correlation coefficients.
• Cannabis quantity, alongside frequency, significantly predicted cannabis problems and dependence severity.
• Concurrent and discriminant validity were established.
• Marijuanilla use did not increase participants' cravings.

Conclusions:

• Marijuanilla may be a reliable and valid tool for reporting grams of cannabis use.
• This comprehensive assessment method is particularly relevant for clinical trials and epidemiological studies requiring precise cannabis use estimates.
• Further research may be needed to refine collateral corroboration methods.