Wednesday 18 April 2012

Correlation, causation, and alcohol

It isn't hard to find studies linking heavy alcohol use to bad social outcomes; it's harder to find ones that adequately correct for individual risk-seeking behaviour.

A few relevant bits of news this past week.

Teenagers who drink are more likely to have played the "choking game". Now I'll take this one with a fair bit of scepticism; it isn't hard to imagine that a fair number of the 6% of Oregon eighth-graders who reported that they enjoy asphyxiation might just have been messing around with the survey team. It's the kind of thing I'd have thought was fun as an eighth-grader. But, here's the alcohol connection:
His team's findings are based on a 2009 survey given to more than 5,000 Oregon eighth graders. The researchers found that kids who were sexually active and those who used drugs or alcohol were more likely to have played the choking game.
At least nobody seems to be claiming that alcohol use is a gateway drug to asphyxiation play.

Second bit of news: a French study shows people with more tattoos drink more alcohol.

People with tattoos drink more than their tattoo-less peers, a new study from France suggests.
The researchers asked nearly 3,000 young men and women as they were exiting bars on a Saturday night if they would take a breathalyzer test. Of those who agreed to take it, the researchers found that people with tattoos had consumed more alcohol than those without tattoos, the researchers said.
Previous studies have shown that tattooed individuals are more likely to engage in risky behaviors, such as unprotected sex, theft, violence and alcohol consumption, compared to people without tattoos.
The researchers suggest educators, parents and physicians consider tattoos and piercings as potential "markers" of drinking, using them to begin a conversation about alcohol consumption and other risky behaviors.
Again, nobody seems to be claiming that alcohol's a gateway drug to getting tattoos. Both of these point to underlying risk-preference as driving outcomes.

Finally, this one points to a more causal relationship. I'm not sure that causality is all that strongly established, but here's the abstract via Bakadesuyo:
A within-person multilevel approach was used to model the links between alcohol use and sexual behavior among first-year college students, using up to 14 days of data for each person with occasions (Level 1, N = 2879 days) nested within people (Level 2, N = 218 people; 51.4% male). Between-persons (Level 2) effects were gender, relationship status, person means of alcohol use, and alcohol-sex expectancies for sexual affect and sexual drive. Within-person (Level 1) effects were weekend days, number of drinks consumed, and the interaction between drinks consumed and alcohol-sex expectancies. Independent of average alcohol use, consuming more drinks on a given day was associated with a greater likelihood of oral sex and with experiencing more positive consequences of sex that day. Significant Alcohol Use × Alcohol-Sex Expectancies interactions were found for oral sex and total sex behaviors, indicating that individuals with more positive expectancies were more likely to have sex after drinking. The negative association between drinks and condom use was at a trend level of significance. Results support the potential for promoting sexual health by focusing on cross-behavior expectancies among late adolescents.
The full paper is here. I still wonder whether the within-person design isn't picking up that the same person will behave differently when going out "for a good time" than he or she would on average otherwise. But, the paper at least suggests that if we're worried about an "alcohol leads to more sex" relationship, we should just maybe put some weight on that this might not be a bad thing on average.

We might also note that there's some evidence that reported correlations between drinking and risky sexual activity are driven by underlying risk preference as well. The linked paper finds that people who use condoms when sober also use them when drinking, and that those who don't when sober, don't when drinking. The researchers there also worry that extensive public warnings about that heavy drinking leading to risky sex may well prime people to do exactly that:
Based on a critical review of this literature, we conclude that it is imprecise (and even misleading) to disseminate the message that alcohol leads to sexual risk behavior. Other authors (Bolton et al., 1992) have noted that if there is no association at the event-level (and therefore no causal association) then disseminating this message may have the effect of giving people an excuse to engage in risk behavior when drinking. This idea is plausible, especially when expectancy theory is taken into account. Because alcohol expectancies can be acquired from a variety of sources other than personal experience (Goldman et al. 1999), delivering a message that alcohol use proximal to sexual activity causes riskier sexual behavior may have the effect of “teaching” sex-related alcohol expectancies to intervention participants who may not have previously held them, and may reinforce expectancies in other participants.
I worry about this too. There's pretty wide variation across countries in how people behave after drinking. Breaking the expectation that drinking gives you an excuse to do dumb things might be more important than reducing drinking. Alcohol use should be something that adds to the probability of being charged and punished when committing offences rather than being exculpatory.


  1. Eric - I agree that studying the correlation between alcohol and other outcomes without controlling for the factors that cause people to drink in the first place is problematic. "Self-medication" is the phrase that's used to describe the use of alcohol to cope with depression, bipolar disorders, etc.

    The underlying cause of Mum screaming at her kids or passing out in the afternoon or puking on the stairwell might be a mental health disorder, and her alcohol abuse just a manifestation of her mental health struggles.

    But that doesn't mean Mum screaming at her kids or passing out or puking is not a problem.

    1. I'm with you. And when that Mum shows up at family court, that she's a horrible drunk should make it more likely that the State changes custody arrangements rather than taking it as an excuse for bad behaviour.

  2. I don't know what the situation is in New Zealand, but in Britain it's illegal to advertise alcohol in a manner which implies that its consumption increases the chance of achieving "sexual success". If, as the study finds, "consuming more drinks on a given day was associated with a greater likelihood of oral sex and with experiencing more positive consequences of sex that day", it looks like our advertising code is not evidence-based.

    1. An excellent point. And alcohol companies are also prohibited from saying things like "Drinking in moderation is known to substantially reduce your risk of death. For your health, please drink every day, in moderation."

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    1. Peter, there's a strange beauty to your comments. This one went a tetch over though.

  4. I think the focus on risk taking as a third variable that explains both alcohol consumption and another behaviour is a bit narrow. Here are a few other candidates, from the top of my head (with some overlap): time discounting, impulsivity, sensation seeking, social control, preference for norm-breaking behaviour, low agreeableness.

    1. Totally agreed. I was using "enjoying risk" as a broad catch-all term.