Wednesday, 12 June 2019

The alcohol made them do it

Alcohol has well-documented effects on a range of harms such as drunk driving (almost by definition), violence, poor health, and mortality. However, the causal evidence for alcohol's effect on a range of less serious harms is less clear - things like risky sexual activity and other substance use. A new article by Jason Fletcher (University of Wisconsin-Madison), published in the journal Contemporary Economic Policy (ungated earlier version here), aims to fill that gap.

It is trivial to show that access to alcohol is correlated with measures of harm. The challenge with any study like this is to show that access to alcohol has a causal effect on the harm. That is, that the observed correlation represents a causal effect, and is not the result of some other factor. Fletcher does this by exploiting the Minimum Legal Drinking Age in the U.S. (of 21 years of age), and using a regression discontinuity approach. Essentially, that involves looking at the measures of harm and how they track with age up to age 21, and then after age 21. If there is a big jump upwards between the time before, and the time after, age 21, then plausibly you could conclude that the sudden jump upwards is due to the onset of access to alcohol at age 21. This approach has previously been used to show the impact of access to alcohol on arrests and on mortality. In this paper, Fletcher instead focuses on:
...drinking outcomes, such as any alcohol use, binge use, and frequency of use as well as drinking-related risky behaviors, such as being drunk at work; drunk driving; having problems with friends, dates, and others while drinking; being hung over; and other outcomes.
He uses data from the third wave of the Add Health survey in the U.S., which occurred when the research participants were aged from 18-26 years old. He analyses the results all together, and separately by gender, and finds that:
...on average, access increases binge drinking but has few other consequences. However, the effects vary considerably by gender; where females (but not males) are more likely to initiate alcohol use at age 21, males substantially increase binge drinking at age 21. In addition, males (but not females) face an increased risk of problems with friends and risky sexual activity at age 21. There is also some evidence of an increase in drunk driving and violence.
Interesting results, but not particularly surprising. Fletcher then tries to draw some policy implications on what would happen if the MLDA was reduced, by looking at differences between young people living with their parents and those not living with their parents. He finds that: harm reduction associated with binge drinking for those individuals living with their parents around age 21; in fact, individuals living with their parents (regardless of whether they are in school) have larger increases in alcohol-related risky behaviors than individuals living away from their parents.
He uses that result to suggest that parents are not good at socialising their children into safer drinking behaviours (and the results, on the surface, suggest this because those living at home engage in more risky behaviour after they attain age 21. However, there is another interpretation that Fletcher doesn't consider. Those who are not living at home might be more likely to be drinking alcohol before age 21, and so experiencing some of the negative impacts earlier. So, those living at home may be simply catching up to their peers, when they are 'allowed' to drink. Maybe that strengthens his other results.

Overall, the paper doesn't tell us much that wasn't already known, although the causal aspect of the study is a nice touch. The differences by gender were a bit more surprising, and hopefully there are other studies that can work further in this area to test them further.

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