Researchers found that conducting surveys at medical marijuana dispensaries produced data with minimal selection or respondent bias, validating this as a reliable method for studying medical cannabis patients.
Read this if you work in cannabis research methodology or want to know whether dispensary-based studies can be trusted.
Both selection bias and respondent bias were minimal in dispensary-based surveys of medical cannabis patients.
What the researchers found
Medical marijuana users are a "hidden population" that is difficult to access through traditional survey methods. Researchers from UCLA evaluated whether conducting surveys at dispensaries introduces systematic biases that would undermine the results.
They used a two-stage venue-based sampling approach and tested for two types of bias: selection bias (whether participating dispensaries differed systematically from non-participating ones) and respondent bias (whether patients who completed surveys differed from those who declined).
Both types of bias were generally absent. The dispensaries that participated were representative of dispensaries overall, and the patients who responded were representative of the broader patient population. This validation means that research findings from dispensary-based surveys can be used to inform policy and clinical practice with reasonable confidence.
Why it matters
Reliable data on medical cannabis patients is essential for evidence-based policy. This study validates a practical method for collecting that data, showing that dispensary-based research can produce findings that represent the broader population of medical cannabis users in a given area.
The numbers in context
Selection bias was generally absent among participating dispensaries. Respondent bias was minimal among survey completers. Results were from the UCLA Medical Marijuana Study in Los Angeles.
How the study worked
The study used the venue-based sampling procedures from the UCLA Medical Marijuana Study, employing a two-stage approach. Statistical analyses compared participating vs non-participating dispensaries and responding vs non-responding patrons on available characteristics.
What this study cannot tell us
The study was conducted in Los Angeles, where dispensary culture and patient demographics may differ from other regions. Patients who obtain medical cannabis outside of dispensaries (home growing, online) are not captured. The methodology assumes dispensaries are the primary access point, which may not hold in all jurisdictions.
How to read the evidence
Moderate evidence from a methodological validation study using established statistical approaches to assess bias.
When this study was published
Published in 2016. Dispensary-based research has since become common in medical cannabis studies.
The bigger picture
As medical cannabis programs expand, policymakers need reliable data on who uses medical cannabis, why, and with what outcomes. This methodological validation makes the case that dispensary-based surveys are a viable and trustworthy data source.
Questions still open
- Does this methodology work in states with different dispensary models? Would online surveys of medical cannabis patients complement dispensary-based approaches? How should researchers handle states where home cultivation is the primary access method?
Common questions
Can we trust research done at dispensaries?
Why is this important?
Read the original research
Assessing Sample Bias among Venue-Based Respondents at Medical Marijuana Dispensaries.
Journal of psychoactive drugs, 48(1), 56-62
Citation
Thomas, Crystal; Freisthler, Bridget. (2016). Assessing Sample Bias among Venue-Based Respondents at Medical Marijuana Dispensaries.. Journal of psychoactive drugs, 48(1), 56-62. https://doi.org/10.1080/02791072.2015.1127450
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