Evaluating possible intended and unintended consequences of the implementation of alcohol minimum unit pricing (MUP) in Scotland: a natural experiment protocol

Introduction Scotland is the first country to carry out a national implementation of Minimum Unit Pricing (MUP) for alcohol. MUP aims to reduce alcohol-related harms, which are high in Scotland compared to Western Europe, and to improve health equalities. MUP is a minimum retail price per unit of alcohol. That approach targets high-risk alcohol users. This work is key to a wider evaluation that will determine whether MUP continues. There are three study components. Methods and Analysis Component 1 sampled an estimated 2800 interviewees at a baseline and each of two follow ups from four Emergency Departments in Scotland and Northern England. Research nurses administered a standardised survey to assess alcohol consumption and the proportion of attendances that were alcohol-related. Component 2 covered six Sexual Health Clinics with similar timings and country allocation. A self-completion survey gathered information on potential unintended effects of MUP on alcohol source and drug use. Using a natural experiment design and repeated cross-sectional audit, difference in difference between Scotland (intervention) and North England (control) will be tested for outcomes using regression adjusting for differences at baseline. Differential impacts by age, gender and socioeconomic position will be investigated. Component 3 used focus groups with young people and heavy drinkers and interviews with stakeholders before and after MUP implementation. The focus groups will allow exploration of attitudes, experiences and behaviours, and the potential mechanisms by which impacts arise. The interviews will help characterise the implementation process. Ethics and Dissemination Study components 1 and 2 have been ethically approved by the NHS, and component 3 by the University of Stirling. Dissemination plans include peer-reviewed journal articles, presentations, policy maker briefings and, in view of high public interest and the high political profile of this flagship policy, communication with the public via media engagement and plain language summaries. Strengths and limitations of this study This evaluation adopts multiple methods to help establish whether MUP has caused changes in alcohol-related attendances using a natural experiment design, which is the most appropriate for this topic as a randomized controlled trial would not be feasible. Our study exploits divergences in Scottish and English alcohol policy to evaluate the effectiveness of an all-beverage MUP for the first time, and evaluates both positive and possible negative impacts of minimum unit pricing of alcohol; such negative impacts might include use of other sources of alcohol, other substances, or reduction in money available for essentials. The Northern English control group is likely to be comparable to Scotland because of geographical proximity and similar levels of deprivation, but we also assess the external validity of our sample by reference to routine data on attendances at Emergency Departments and Sexual Health Clinics. There is the potential to follow up individuals through longer term data linkage, for which we will obtain respondents’ permission, thus adding a cohort dimension to the initial cross-sectional approach. The main limitation is that the non-randomised design risks selection bias, for example in the differential selection of intoxicated attendees for interview