Triangulating web & general population surveys: Do results match legal cannabis market sales?

Background: This paper combines complementary attributes of web and general population surveys to estimate cannabis consumption and spending in Washington State. It compares those estimates to legal sales recorded by the state's seed-to-sale tracking system, and thus exploits a rare opportunity to contrast two independent estimates for the same cannabis market. This sheds light on the question of whether nontrivial amounts of black market sales continue even after a state allows licensed production and sale. Methods: Prevalence of past-month use is estimated from the 2015/16 U.S. National Survey on Drug Use and Health, adjusted for under-reporting. Estimates of consumption and spending per user broken down by age, gender, and frequency of use are developed from RAND's 2013 survey of cannabis users in Washington State. Supply side estimates come from the Washington State Liquor and Cannabis Board's seed-to-sale tracking system. They are expressed in terms of spending, equivalent-weight of flowers, and THC, with THC for edibles imputed using a machine learning technique called random forests. Results: For the period July 1, 2016 to June 30, 2017, Washington's seed-to-sale data record sales from licensed cannabis stores of $1.17B and across all products an amount of THC that is equivalent to roughly 120-150 MT of flower. Survey responses suggest that amounts spent and quantities consumed are larger than that, perhaps on the order of $1.66B and over 200 MT, respectively. Conclusion: A perfect match is not expected because of sales to tourists, residual black market activity, production for medical purposes, and diversion across state lines. Nonetheless, the results suggest that three years after state-licensed stores opened, there remained considerable consumption of cannabis supplied outside of the licensed system.