Monday 19 November 2012

Causes and consequences

One thing that struck Matt and me when going through the alcohol literature was co-morbidity between heavier alcohol use and a whole pile of other bad things. We wrote:

We also worry that the aetiological fractions used may not account adequately for comorbidity between alcohol use and pre-existing mental disorders. The aetiological fractions used ascribe between twenty-five and thirty percent of male suicides to alcohol; in other words, if alcohol disappeared, the suicide rate would drop by more than a quarter for adult males over the age of twenty. As alcohol use can often be a form of self-medication among those with mental illness, whether alcohol plays that substantial a
causal role in suicides is debatable. Ross (1995) finds that more than half of those with an alcohol disorder have a lifetime comorbid psychiatric disorder. Among subcategories for which data is presented, alcohol abusers have rates of mood disorders and anxiety disorders 2.3 and 1.7 times that of non-abusers. While 9% of alcohol abusers report antisocial personality disorders, only 0.6%  of non abusers report such disorders. The Mental Illness Fellowship of Australia (2005) notes that those with bipolar disorder are eleven times more likely to engage in harmful drug or alcohol use than is the general population. Kessler et al (1997) find that those with long term alcohol abuse or dependence not only have a high probability of also exhibiting another mental disorder but also that comorbid DSM-IIIR disorders tend to predate alcohol use disorders.  
Some people with pre-existing disorders self-medicate with alcohol and consequently are better off than they would have been but worse off than average; their variance from average outcomes is counted as a cost of alcohol. Some people with pre-existing disorders self-medicate with alcohol and consequently are worse off than they otherwise would be; the total amount of their variance from average outcomes is counted as a cost of alcohol rather than only the incremental worsening from their individual baselines. This stuff isn't easy. But the direction of the bias is pretty clear.

Emma Hart at Up Front [not guaranteed safe for work] points to more work in similar vein: bisexuals are more likely to have problems with binge drinking. And it's because of underlying social pressures. She writes:
Here’s a clue, guys: it’s not the drinking, it’s the why they’re drinking. Take a lesson from, and maybe work out why I link to so many stories there instead of at your place: Exclusion Leading Some Bi Youth to Binge Drink. The drinking is not the problem, it’s one of the symptoms of the problem. 
She then quotes from the study's surveys of young binge-drinking bisexuals:
I drink more when I’m under high stress, when I’m stressed out, and maybe sometimes at parties when, after conversations with people, where they want to know, no one gets the bi thing. It’s really hard to explain. Quite a bit because you get people who want to know why you are not lesbian, why you are not straight, and I kind of feel that, it’s slightly easier to be one or the other, like I envy some of my friends who are gay, I’m like you know who, you know you’re there and no one questions it. But I get questioned all the time, and I find that frustrating sometimes.
Arahia: You kind of drink more so you can say the next day: “Oh, I was just drunk, you know. It didn’t mean anything really.” Sometimes it does, sometimes. But if you wake up the next morning with a huge hangover, you can say to the person: “Oh god, it didn’t mean anything. I was just so wasted.”

Fiona: “Didn’t mean to grope you. I was just drunk.”

Arahia: It is such a good excuse.

Fiona: And I think bi people definitely use it as more of an excuse than any other sexual orientation.
Sometimes, use of alcohol is inframarginal to whatever other behaviour we're measuring, whether crime or sex. Sometimes, alcohol use helps people to get over their inhibitions and do utility-enhancing things. And, sometimes alcohol use leads people to make mistakes. We overstate the costs of alcohol when we assume that alcohol's role is always causal and always negative, or when we assume away the positive consequences.


  1. Eric - I agree with your basic point about ascribing to alcohol behaviours that might be due to underlying mental health or other causes, and thus misrepresenting the negative impacts of alcohol.

    People self-medicate with alcohol because in part because it can be hard to get access to good quality and affordable mental health treatment, and in part because the major anti-depressants, e.g. Prozac and related, don't work well for people with bi-polar type disorders.

    However I don't think I would conclude from this that use of alcohol is inframarginal. It's as plausible that use of alcohol is multiplicative. E.g. probability of abusing spouse = function of (presence of mental health issues * use of alcohol). All that can be said with any degree of certainty is that, when we're unable to control for people's underlying mental health issues, we will end up with a biased estimate of the impact of alcohol on behaviour.

  2. No disagreement, Frances. There are definitely some whose pre-existing conditions are worsened through alcohol use; some who develop conditions due to alcohol use; and, some whose conditions are ameliorated due to alcohol use. Counting everything as being caused by alcohol assumes that all of the costs associated with conditions where people use alcohol are caused by alcohol; the bias there only works in one dimension.

  3. That's right, all the traffic accidents with drivers who have alcohol readings are ticked off as 'alcohol accidents'
    There is no possible account for aggressive driving, dangerous driving, or sleepy driving. The obsession with alcohol is because it is measurable at the scene, unlike stupidity, sleepiness, aggression.
    Your point about co morbidity with alcohol implies that these other conditions may well be part of tendency to misuse alcohol.
    People [ especially alcoholics] often like to believe that you get zapped by 'alcoholism' within personality make up, and that it is a condition entirely unto itself.
    Now that particular function of alcoholism which leads to uncontrolled drinking usually [ not always ] takes time to develop, and it is reasonable to think there would be other existing factors.

  4. Eric, we're talking about estimating the marginal effect of alcohol. Your point is that if Y=a+b*mental health + c* alcohol, and mental health is unobserved and positively correlated with alcohol use, we will end up overestimating dY/d(alcohol), the impact of alcohol on Y (for b>0). And this is true.

    My point is that, if Y=a+b*(mental health)(alcohol), then the true marginal effect of alcohol is dY/dalcohol=b*mental health. In this situation, the estimated coefficient on alcohol (again, mental health being unobserved) could be either higher or lower than the true marginal effect of alcohol use for any one individual. Note that here there is no single marginal effect of alcohol use; the impact of alcohol varies from person to person.

    So I agree with you about the importance of comorbidity, but don't conclude from this that the best attitude towards alcohol is don't-worry-be-happy. It might be that the best policy is to take more agressive action against alcohol abuse.

  5. The problem is that folks aren't estimating marginal effects. They're taking average cohort outcomes among those who drink and those who don't and calling the entire difference the cost of alcohol. Where pre-existing mental illness can be one of the drivers of harmful alcohol use, even in the cases where alcohol use makes the pre-existing condition rather worse, it is a mistake to ascribe all differences in outcomes to booze; the counterfactual world of no alcohol use would still have the "not drinking in the counterfactual but are drinking in the factual" cohort having worse outcomes in the counterfactual.