The District Health Boards in New Zealand are busy cancelling elective surgeries and non-urgent care in order to deal with the ongoing surge in coronavirus cases. In 2020 and 2021, South Africa took things much further, on a number of occasions banning the sale of alcohol in order to reduce alcohol-related hospital presentations and injuries (see here). This new working paper by Kai Barron (Wissenschaftszentrum Berlin für Sozialforschung) and co-authors looks at the impact of the second ban (from 13 July to 18 August 2020) on mortality and other related outcomes. This particular ban makes a good natural experiment because:
...it was unexpected. The alcohol ban was announced in the evening of Sunday, July 12, 2020, and came into immediate effect from Monday morning on July 13, 2020. Second, it was implemented in the middle of the so-called “Level 3” COVID-19 policy response period during which time other policies and regulations were largely held constant.
In other words, no one could have anticipated the ban and adjusted their behaviour beforehand, so it provides a clean 'break' in the time series data, and no other policy could make it difficult to isolate the effect of the alcohol ban. [*]
Barron et al. focus on the effect on mortality due to unnatural causes (which includes road traffic injuries, interpersonal violence, and suicides) in the first instance. They use data on daily mortality from 2017 to 2020, and employ a difference-in-differences approach. I haven't seen it employed in quite this way before. They essentially treat the alcohol ban dates in each year from 2017 to 2019 as a control, and the same dates in 2020 as the treatment period. So, their difference-in-differences is the difference between the alcohol ban dates and the rest of the year in 2020 compared with the difference between the alcohol ban dates and the rest of the year in 2017 to 2019. In one of the footnotes, they argue that this approach:
...can be justified when there is strong year-on-year temporal regularity in the outcome of interest.
There does seem to be a persistent trend across the years 2017 to 2019, and Barron et al. control for day-of-the-week effects, week-of-the-month effects, and month fixed effects, which should capture most of the regularities over time. Their key results are best summarised in Figure 2 from the paper:
Notice that there's a drop in mortality from unnatural causes in 2020/21 every time there was an alcohol ban in 2020. Barron et al. are focused on the middle period, where the ban was unanticipated, and not correlated with other policy changes. The effect looks smaller there, but in their preferred econometric model they find that:
...the alcohol ban reduced unnatural mortality by 21.99 deaths per day...
That doesn't sound like a lot, but it represents about a 14 percent reduction in deaths from unnatural causes. Barron et al. then go on to show that:
For men, the pattern is similar to that observed in the population as a whole, with the estimates indicating that the alcohol ban reduced mortality by approximately 21 deaths per day... For women, we find no significant impact of the alcohol ban on mortality.
That shouldn't be too surprising, given that men are at greater risk of deaths from unnatural causes. And then when they look at young adults (aged 15 to 34 years) they find that:
...the alcohol ban reduced mortality amongst men in this age-group by approximately 12 deaths per day... and may have had a small impact on the mortality of younger women.
So, overall, the alcohol ban reduced mortality from unnatural causes, almost entirely among men, and over half of the reduction was among young men. Barron et al. then go on to report results week-by-week using an event study, and it looks like most of the effect is concentrated in the first few weeks of the ban. That suggests that there might be some adaptation, or that there was less compliance with the ban as it extended over time. Those results should caution us from assuming that a complete prohibition on alcohol would lead to a large improvement in mortality.
Finally, using police data Barron et al. find that there were:
..at least 77 fewer homicides, 790 fewer assaults and 105 fewer rape cases reported per week during the alcohol ban period in comparison to the preceding five weeks. These constitute a drop in each outcome of 21%, 33% and 19% respectively.
Altogether, this supports a conclusion that the alcohol ban reduced interpersonal violence, leading to less alcohol-related harm, and lower mortality. We know that alcohol is associated with harm. This study has given us a particularly clean estimate of just how much harm it can cause.
[HT: Marginal Revolution]
*****
[*] Actually, that's not quite true, as there was also a curfew put in place, but the curfew lasted much longer than the alcohol ban, and Barron et al. show that removing the ban but leaving the curfew in place was associated with a bounce back in mortality and other outcomes.
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