Evaluating the effects of minimum unit pricing in Scotland on the prevalence of harmful drinking: a controlled interrupted time series analysis
Original Research
Abstract
Objectives
In May 2018, the Scottish Government introduced a minimum unit price (MUP) for alcohol of £0.50 (1 UK unit = 8 g ethanol) to reduce alcohol consumption, particularly among people consuming alcohol at high risk levels.
This study aimed to evaluate MUP’s impact on the prevalence of high risk alcohol use among adults in Scotland.
Study design
This was a controlled interrupted monthly time series analysis of repeat cross-sectional data collected via 1-week alcohol consumption diaries from adult alcohol users in Scotland (N = 38,674) and Northern England (N = 71,687) between January 2009 and February 2020.
Methods
The primary outcome was the proportion of alcohol users consuming at high risk levels (>50 [men] or >35 [women] units in diary week).
The secondary outcomes included the proportion of alcohol users consuming at hazardous (≥14–50 [men] or ≥14–35 [women] units) and low risk (<14 units) levels and measures of beverage preferences and alcohol use patterns.
Analyses also examined the prevalence of high-risk alcohol use in key subgroups.
Results
There was no significant change in the proportion of alcohol users consuming at high risk levels or moderate levels after the introduction of MUP.
The proportion consuming alcohol at hazardous levels fell significantly by 3.5 percentage points.
There were no significant changes in other secondary outcomes or in the subgroup analyses after correction for multiple testing.
Conclusions
Introducing MUP in Scotland was not associated with reductions in the proportion of alcohol users consuming at high risk levels but did reduce the prevalence of hazardous alcohol use (≥14–50 [men] or ≥14–35 [women] units).
This adds to previous evidence that MUP reduced overall alcohol consumption in Scotland and consumption among those consuming alcohol above low risk levels.
Background
The Scottish Government introduced a minimum unit price (MUP) for alcohol on May 1, 2018. This means retailers in Scotland cannot sell alcohol to consumers for less than £0.50 per unit (1 UK unit = 8 g/10 mL ethanol).
In 2018, 44% of off-trade alcohol units were sold below £0.50 per unit in Scotland. The associated legislation includes a ‘sunset clause’ that requires MUP to end after 6 years unless the Scottish Parliament votes for it to continue. To inform this vote, the Scottish Government commissioned NHS Health Scotland (now part of Public Health Scotland [PHS]) to conduct a wide-ranging evaluation of MUP and report its findings in mid-2023.
MUP is a well-targeted policy that concentrates price increases on the cheapest alcohol that is disproportionately purchased by those consuming alcohol at hazardous levels (i.e. 14−35 units a week for women or 14–50 units a week for men; approximately 20% of the population) or high-risk levels (approximately 5% of the population).
Evidence is required on whether MUP effectively reduces high-risk alcohol consumption.
Evaluation findings to date suggest the policy was implemented largely as intended and reduced off-trade alcohol sales in Scotland by 3.5%.
However, analyses of changes in alcohol consumption among heavier alcohol users report mixed findings. Analyses of household panel data show that the fifth of households that purchased most alcohol pre-MUP reduced their purchasing by more than the remaining four-fifths after the policy was introduced.
In contrast, an analysis of market research alcohol consumption diary data suggests MUP led to reduced alcohol consumption for the lightest alcohol use 90% of women but no statistically significant change for the highest consuming 10%, whereas consumption among men did not change significantly except for an increase among the highest consuming 5%.
However, these previous studies were limited by short pre- and post-intervention time series (e.g. 2015–2018) and in some cases had full-year breaks in the series where data were not available.
They also focus only on levels of consumption in different groups rather than the overall prevalence of hazardous and high-risk alcohol use across the population.
This study aims to provide further evidence regarding the impact of MUP on people consuming alcohol at high-risk levels by
- evaluating the impact of the policy on the prevalence of high-risk alcohol use among adult alcohol consumers in Scotland,
- also evaluating the impact of MUP on the prevalence of low-risk and hazardous alcohol use, and
- developing understanding of the mechanisms of any identified effects by evaluating the impact of MUP on the beverage preferences and alcohol use occasion dynamics (e.g. occasions per week) of people drinking at high-risk levels and of how impacts differ across sociodemographic groups.
Primary outcome
There was no significant change in the proportion of alcohol users consuming at high-risk levels in Scotland.
This finding was consistent across the sensitivity analyses that used the subsequent data point in the series as the intervention point (June 2018), controlled for the rollout of Universal Credit in Scotland and included a term to capture a change in the postintervention trend (Supplementary Table 2).
Secondary outcomes
Immediately after the introduction of MUP, there was a significant reduction in the proportion of alcohol users consuming at hazardous levels in Scotland.
However, there was no significant change in the proportion of alcohol users consuming alcohol at low-risk levels. This model controls for a breakpoint in the data series at the beginning of 2017.
There were no significant changes in the mean proportion of alcohol consumption in the diary week that is accounted for by strong beer, strong cider, vodka, or consuming alcohol in the off-trade. These findings were consistent in sensitivity analyses using an uncapped measure of alcohol consumption (Supplementary Table 2).
There were also no significant changes in the patterns of alcohol consumption during the diary week for most outcome measures, specifically, the number of alcohol consumption days per week, maximum number of units consumed in a single occasion during the week and the number of occasions involving consuming alcohol alone, including in sensitivity analyses using uncapped alcohol consumption.
The direction of effect indicated a reduction in the mean number of alcohol consumption days per week, the mean number of units per occasion and the mean number of units per week for alcohol users consuming alcohol at high-risk levels.
The magnitude of these reductions was similar to the 3.0–3.5% fall in alcohol sales by volume found in analyses of population-level sales data, although the uncertainty around the effect estimates was high and the direct of effect reversed in sensitivity analyses.
For people consuming alcohol at high-risk levels, there was a statistically significant drop in the mean number of units consumed per occasion and mean number of units consumed per week.
However, these results were not robust based on the sharpened q-values, which adjust for multiple testing (q = 0.172) or the sensitivity analysis using uncapped alcohol consumption, which found no significant change.
Interpretation and meaning
The results suggest the introduction of MUP in Scotland did not lead to a decline in the proportion of adult alcohol users consuming alcohol at high-risk levels. It also did not lead to any change in the types of alcoholic beverage consumed by this group, their alcohol use patterns, the extent to which they consumed alcohol while on their own or the prevalence of high-risk alcohol use in key subgroups.
However, the secondary analyses suggest the proportion of alcohol users consuming at hazardous levels did decline.
The key strengths of this study are the large sample size and long time series provided by Alcovision, the controlled interrupted time series design and the testing of a wide range of secondary outcomes.
The decline in the prevalence of hazardous alcohol use in this study’s findings is consistent with the decline in alcohol consumption found in previous evaluations of MUP in Scotland.
However, the lack of evidence for a decline in the prevalence of high-risk alcohol use arising from MUP is contrary to model-based evidence that informed the introduction of the policy. It also adds to previous inconsistent evidence on the impact of MUP in Scotland on those consuming at high-risk levels.
One important caveat is the measures used here and in previous studies do not map directly onto the standard measures of hazardous and high-risk alcohol use used in key studies that informed the policy decisions on MUP. Although those standard measures relate to individuals’ typical weekly alcohol use, the evaluation studies use measures of household purchasing or individuals’ alcohol consumption in the previous week. Moreover, the standard measures typically find approximately 5% of Scottish adults consume alcohol at high-risk levels, but the studies of household purchasing only disaggregate the population into quintiles, while Table 1 suggests approximately 10% of adults consume alcohol at high-risk levels. This implies caution is needed when comparing findings and translating categories of alcohol users between evidence sources.
Nonetheless, the study’s findings add to consistent evidence that MUP led to reductions in alcohol consumption among those consuming alcohol above low-risk levels but offers less certainty regarding the impact on those consuming alcohol at high-risk levels.
The lack of change in the prevalence of high-risk alcohol use may arise for several reasons.
First, people consuming alcohol at high-risk levels may be less responsive to price changes than alcohol users with lower levels of consumption. Previous qualitative research and studies of purchasing behaviour among people with alcohol dependence (i.e. a group that comprises approximately 20% of those consuming alcohol at high-risk levels in the United Kingdom and thus 1% of the overall population) supports this view.
However, the very large price increases imposed by MUP on people consuming alcohol at high-risk levels, their inability to switch to cheaper products and clear evidence of successful policy implementation and compliance, mean their price responsiveness would need to be extremely low to negate any impact on consumption.
Second, the changes in high-risk alcohol use may have primarily affected those consuming at the highest levels and thus not affected the prevalence of high-risk alcohol use.
However, a recent study of the impact of MUP on people with alcohol dependence found no clear evidence of reduced alcohol consumption. The researchers have not presented any analyses examining this hypothesis because of small sample sizes and unreliable measurement of very high alcohol consumption levels.
Third, people consuming alcohol at high-risk levels may have adopted unsustainable strategies to temporarily manage the price rises caused by MUP.
For example, there is evidence a minority of people with alcohol dependence responded to MUP by reducing spending on essentials, borrowing money and using their savings. Longer term evaluation may therefore be required to fully understand the policy’s impact on consumption.
Finally, the current MUP may be set too low to generate detectable impacts.
The £0.50 was initially proposed circa 2011 and would have affected approximately 70% of off-trade alcohol units sold at that time compared with 44% in 2018 when the policy was introduced. The real-term value of the MUP has also fallen over time due to inflation.
A review of the current £0.50 level is currently underway, with public health organisations calling for MUP to be uprated in 2024. Although this weakens the effectiveness of the policy, it is not sufficient to explain the null results identified here because those consuming alcohol at high-risk levels still faced significant price increases.
Further research that would strengthen understanding of the impact of MUP on people using alcohol at high-risk levels include studies of alcohol-related harm.
Such analyses have recently been published, showing a 13.4% reduction in alcohol-attributable deaths and a 4.1% reduction in alcohol-attributable hospitalisations in Scotland.
This provides the most direct evidence on the public health impact of MUP to date. Evidence from other jurisdictions that have introduced MUP, including Wales, Ireland and Australia’s Northern Territory, would ideally strengthen conclusions, but a combination of the confounding from the COVID-19 pandemic and lower availability of high-frequency time series data for evaluation research in other jurisdictions means the Scottish evaluation offers the most robust evidence.
Finally, further understanding of how those consuming alcohol at high-risk levels managed the price rises caused by MUP, if they did not reduce their consumption, would strengthen the understanding of the impact of pricing policies on people at greatest risk from alcohol intake.
Conclusions
MUP in Scotland was not associated with reductions in the prevalence of high-risk alcohol use but was associated with reductions in the prevalence of hazardous alcohol use.
This adds to a wider evidence base that MUP led to a reduction in overall alcohol consumption and consumption among those drinking above moderate levels.