Reliability of an Adaptive Marijuana Purchase Task

Purchase tasks are used to measure the value, or demand, for various substances by assessing the amount of a substance individuals would purchase across a series of escalating prices. Marijuana purchase task (MPT) has been previously developed; however, cannabis can be consumed in various forms and measurements, thus raising questions about the applicability of the MPT across cannabis users. An adaptive MPT was developed to allow participants to select their preferred product (e.g., herbal, dabs) and division (e.g., hits, grams). Little research has been done to assess the temporal stability of these measures. Participants (N = 50, Mage = 35.3) who reported at least monthly cannabis use were recruited via Amazon's Mechanical Turk and completed a baseline and repeated original and adaptive MPT. Seventy-two percent (N = 36) of the sample reported the same preferred product and division. Results indicated that the baseline and repeated original MPT were significantly correlated across all indices (rrange = .37-.73), while the baseline and repeated adaptive MPT was significantly correlated with Pmax (r = .31, p = .029) and Omax (r = .57, p < .001). Permutation testing comparing the difference between the original and adaptive MPT on all indices demonstrated a difference for break point (rdifference = .52, p = .004) and elasticity (rdifference = .94, p = .005). Correlations were lower between participants who switched their preferences on the adaptive MPT. Only elasticity was significantly different (rdifference = .93, p = .012) between tasks among participants who did not switch their preferences. Results provide support that both the original and adaptive MPT are reliable across repeated measurement and demonstrate the importance of assessing cannabis product and division preferences. Public Health Significance This study provides support that the original and adaptive marijuana purchase tasks (MPT) are reliable across repeated measurements for studying associations with cannabis use demand. Further, the adaptive MPT provides additional utility by allowing researchers to compare behavioral and demand associations by cannabis product.