Thursday, 8 May 2014

Drinking behaviour, drink driving, and more on the drinking age

I found this article on texting yourself to moderate your drinking behaviour interesting. From the article:
A University of Auckland researcher is about to begin a full research trial where the participants will get a text message like this, written by themselves, to remind them not to drink too much...
"My premise is most of us are reasonably intelligent people. So why don't we tap into that and allow people to create their own messages."
The premise is that people compose text messages to themselves that they will receive later in the night, reminding them not to over-indulge, and that messages from themselves are more likely to be successful than messages from others. Karen Renner (PhD candidate at the University of Auckland claimed that her initial study showed a 23 percent reduction in alcohol-related harms. I can't find any published study thus far, but if you're interested her research protocol is recorded here. It appears she is using YAAPST (Young Adult Alcohol Problem Severity Test), which "is a sensitive measure for mild alcohol-related consequences, such as hangover, feeling sick, being late for work/school, etc." Reducing hangovers by 23 percent is a useful outcome. I look forward to the results of the wider study, which you can join as a participant here.

However, while thinking about this study it is worth noting that even as "relatively intelligent" people we are notoriously bad at self-control. If we were rational decision-makers, we would realise that drinking too much increases the risk of getting ourselves (or others) into trouble. That's why behavioural economists advocate for pre-commitments - prior (and irreversible) actions that commit us to a certain course of action - Dan Ariely discusses a few pre-commitments here (wearing the granniest pair of granny underwear to ensure you won't bed a guy on the first date, priceless).

I wonder whether a text message to yourself constitutes a large enough pre-commitment to modify your behaviour. There is little cost to you of ignoring a text message, not matter how coarse the language you use. In other words, it's not binding (see here for other examples). An interesting alternative might be, if you're not home by some self-imposed curfew your home computer gives money to charity (unless you're home to stop it!), or to your ex or other person you'd rather not give money to. There's got to be an opportunity for a new app in there (and now I've posted the suggestion, if you develop one you ought to cut me in!).

Speaking of drinking behaviour, there is a recent paper in the Journal of Health Economics by Frank Sloan, Lindsey Eldred and Yanzhi Xu (all of Duke University), which looks at the behavioural economics of drink driving (gated, and I can't see an ungated version anywhere online). Using survey data from the U.S., they investigated a number of questions about the behaviour of drink drivers, including:

Question: "Does the cognitive ability of persons who report they drank and drove in the past year differ from those who did not? Perhaps drinking and driving is a byproduct of cognitive deficits."

Answer: Possibly not. Drink drivers differed in cognitive ability from non-drink-drivers in only one of their three measures of cognitive ability (self-reported memory).

Question: "Is such behavior attributable to lack of knowledge of DWI laws? One reason for lack of knowledge is that the cost of acquiring the requisite information may be higher for some individuals in part because of lower cognitive ability."

Answer: Drink drivers actually have higher knowledge of the DWI laws than non-drink-drivers, so lack of knowledge doesn't explain drink driving.

Question: "Do drinker drivers lack self-control, as indicated by a lower propensity to plan for the future and by greater overall impulsivity?"

Answer: Yes. Drink drivers are more impulsive, and less prone to plan events involving drinking (such as selecting a designated driver in advance). They also find that drink drivers have higher rates of time preference (they place higher values on the present relative to the future than others), and some evidence of time inconsistency and hyperbolic discounting.

One last bit of interest I noted from the article was this:
According to our survey findings, the probability of arrest for DWI, conditional on driving after having had too much to drink is 0.008. Considering the probability of prosecution and conviction for DWI, the probability of a DWI conviction given a drinking and driving episode is about 0.006.
Given that low probability of receiving a penalty, even a rational decision-maker might find that the costs of drink-driving (penalty for drink-driving multiplied by the low risk of being caught and penalised) was lower than the benefits. So it need not be the case that we assume that drink-drivers are irrational to explain their behaviour.

In terms of reducing drink driving, while pre-commitment might seem attractive as a solution (since drink drivers are more likely to lack self-control), it might not work well since drink drivers are less likely to plan ahead and create a pre-commitment not to drink-drive. Forcing the pre-commitment onto recidivist drink drivers (like ignition interlocks, and related driver licensing changes) would seem like an appropriate intervention based on these results.

On a somewhat related note, the week before last I posted a comparison of two studies examining the effects of the change in the drinking age on hospitalisations in New Zealand. Just days after that post, a new paper by Taisia Huckle and Karl Parker (both of Massey University) looking at the effect of the change in the drinking age on alcohol-involved crashes was released by the American Journal of Public Health (ungated PDF version here). Here's the abstract:
Objectives. We assessed the long-term effect of lowering the minimum purchase age for alcohol from age 20 to age 18 years on alcohol-involved crashes in New Zealand.
Methods. We modeled ratios of drivers in alcohol-involved crashes to drivers in non-alcohol-involved crashes by age group in 3 time periods using logistic regression, controlling for gender and adjusting for multiple comparisons.
Results. Before the law change, drivers aged 18 to 19 and 20 to 24 years had similar odds of an alcohol-involved crash (P = .1). Directly following the law change, drivers aged 18 to 19 years had a 15% higher odds of being in an alcohol-involved crash than did drivers aged 20 to 24 years (P = .038). In the long term, drivers aged 18 to 19 years had 21% higher odds of an alcohol-involved crash than did the age control group (P ≤ .001). We found no effects for fatal alcohol-involved crashes alone and no trickle-down effects for the youngest group.
Conclusions. Lowering the purchase age for alcohol was associated with a long-term impact on alcohol-involved crashes among drivers aged 18 to 19 years. Raising the minimum purchase age for alcohol would be appropriate.
The paper was covered by the NZ Herald here. Some of the problems with the paper have been discussed by Thomas Lumley at StatsChat and by Eric Crampton at Offsetting Behaviour, so I won't bother going over the same ground again.

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