The aim of this study was to inform the debate leading up to the New Zealand cannabis referendum by conducting an MCDA with a range of key national stakeholders to identify their preferences for cannabis reform outcomes and in doing so rank cannabis policy reform options. A central aim of our study was to involve a broader range of stake- holders in the MCDA assessment as suggested in recent critiques of MCDA. While these stakeholders possessed practical experience of different aspects of cannabis outcomes, they did not necessarily have de- tailed knowledge of the evidence related to the outcomes of cannabis policy reforms implemented overseas, or the wider research literature on the health and social risks of cannabis use. They also had limited time to digest this research literature and attend a multi-day decision-making workshop . Consequently, to ensure as many stakeholders as possible were able to attend the workshop, much of the development of the MCDA model was completed in advance via a collaborative process with domestic and international cannabis policy experts.

This preliminary work allowed the MCDA workshop to be completed in a single day as stakeholder participants were able to go straight to normative trade-offs assessing projected out- comes from different reform options. From the perspective of the stake- holders,ebb and flow table the MCDA was therefore largely a group discrete choice experiment where they were asked to make comparisons between two alternative projected outcomes that differed in a specified way on a key criterion and reach consensus on the preferred outcome. Developing an MCDA model for evaluating cannabis policy reform options entails four broad stages:  defining the policy reform options,specifying the decision-making criteria and their outcome levels,  determining the relative weights for the different decision-making criteria and related levels, and  ranking the policy reform options based on the relative weighting of the criteria and levels .The two cannabis policy researchers based in New Zealand  initially identified the five key cannabis policy reform decision making criteria  and related levels, by drawing on New Zealand Government documents dis- cussing the overarching policy objectives of cannabis reform , previous New Zealand reports estimating cannabis harms and assessing law reform options, available New Zealand statistics on cannabis use and harm, and the policy evaluation literature from overseas cannabis reforms , 2020 ; Sense Partners, 2018. Criteria 1 – Health and social harm.

The baseline figure of the “health and social harm ”of cannabis use in New Zealand used in the MCDA model of $1.3 billion per year  was taken from the 2016 New Zealand Drug Harm Index commissioned by the New Zealand Ministry of Health . The NZ-DHI provides a comprehensive evaluation of the costs of cannabis use in New Zealand, including the personal and community harm of use and related costs of interventions . The NZ-DHI was written in collaboration with the New Zealand Ministry of Health and other government agencies who provided national statistics on drug use and harm for the report. This method- ology was adapted to New Zealand in 2008 and updated in 2016. The NZ-DHI authors acknowledge a number of gaps and limitations of official statistics which require simplifying assumptions to complete the estimates, including difficulty assigning harms from poly-drug use to individual drug types , quantifying the harm of drug dependency on families, and establishing the causal role of drug use in crime . A limitation specific to cannabis was New Zealand health statistics did not separate natural cannabis from synthetic cannabinoids,flood table recording them together as a combined “cannabinoid ”category . There is evidence from U.S. national data of increasing adult use, frequency of use and cannabis use disorder in legal recreational cannabis states . It has subsequently been noted that only four US states  had established cannabis retail outlets during the period of this study , and those had only been open for a relatively short period of time, suggesting that the longer-term impact of commercial legalization and higher potency legal products on harm is yet to be fully experienced . Evaluations of the impact of cannabis legalisation on youth in the early U.S. recreational legalization states  who implemented largely commercial regimes have found mixed results with meta-analyses suggesting small increases in use .