Evaluating the impact of a multi-buy discount ban on off-trade alcohol sales: a natural experiment in Scotland
A ban on multi-buy discounts of off-trade alcohol was introduced in Scotland in October 2011. The legislation aimed to reduce population alcohol consumption levels and related levels of morbidity and mortality. The aim of this study was to assess the impact of the intervention on alcohol sales, which provide the best indicator of population consumption.
METHODS:
We obtained weekly data on the volume of pure alcohol sold off-trade in Scotland and England & Wales between January 2009 and September 2012. Interrupted Autoregressive Integrated Moving Average (ARIMA) time-series models were used to test for change in off-trade alcohol sales. Models accounted for underlying seasonal and secular trends and were adjusted for disposable income, alcohol prices and on-trade alcohol sales. To provide a concurrent control group, we performed the same analyses using data for England & Wales, where the legislation does not apply. The contrast between effect estimates in Scotland and England & Wales will be measured using a bootstrapping method for multivariate time series models.
RESULTS:
The introduction of the legislation was associated with a 2.6% decrease in per adult off-trade alcohol sales in Scotland (95% CI -5.3 to 0.2%). This decline was largely due to a 4.0% (95% CI -5.4 to -2.6%) decline in wine sales. There were no associated changes in other drink types in Scotland, or in sales of any drink type in England & Wales. Results contrasting effect estimates will also be presented.
CONCLUSIONS:
A ban on multi-buy discounts of alcohol in Scotland was associated with reduced population alcohol consumption. Similar changes were not observed in England & Wales, where the Act does not apply, and potential confounders could not explain the differences in trends. Thus, it is likely that the Scottish decline was due to the legislation rather than unmeasured factors or biases.