Evaluating the effect of minimum unit pricing for unit of alcohol on road traffic accidents in Scotland: a controlled interrupted time-series study

Abstract

Background: Scotland was the first country to implement on May 1, 2018, a minimum unit pricing (MUP) for alcohol volume in beverages to tackle alcohol-related harms. In this study, we assessed the effect of MUP on road traffic accidents (RTAs) after 20 months of its implementation. We hypothesise that MUP would be associated with decreases in RTAs-ie, rises in alcohol prices and consequent decreases in consumption could lead to reductions in drink driving episodes, leading to reductions in RTAs.

Methods: Interrupted time-series regression was used to evaluate the effect of MUP on RTAs (ie, total, fatal, nighttime) and any effect modification across socioeconomic deprivation groups. Data were obtained from the UK Department for Transport. As well as Scotland, RTAs in England and Wales were used as the control group. Covariates for severe weather events, bank holidays, and seasonal and underlying trends were included.

Findings: The number of weekly RTAs per 100 000 population decreased over time in Scotland (2·52 in the 20 months before the intervention and 2·15 after the intervention-ie, a reduction of 15%) and in England and Wales (4·00 in the 20 months before the intervention and 3·76 after the intervention-ie, a reduction of 6%). Inferentially, in Scotland, the introduction of MUP was associated with a 7·2% (95% CI 0·9-13·7; p=0·03) increase in the total number of RTAs. For the corresponding period in England and Wales, a 0·9% (95% CI -2·3 to 3·2; p=0·75) increase was reported. Similar results not supporting the a priori hypothesis were seen for other RTA categories, and no evidence for effect modification was found.

Interpretation: The decrease in alcohol consumption due to MUP found in other studies was not translated into a reduction in the number of RTAs. Because MUP is unlikely to be causally linked to increased RTAs, the most likely explanation of these results is that unmeasured time-varying confounding was present and affected Scotland as well as England and Wales differently.

Funding: None.