Thursday 7 July 2011

Yet another causality fail

Think about couples where spousal abuse is common. Would you expect that partners in those dysfunctional dyads might just be a bit different from other folks, on average? Perhaps more impulsive and higher rate of time preference? Would it be surprising then to find on survey data that abusive spouses also exhibit other behaviours consistent with impulsiveness?

The Press happily takes the correlation as causal:
Binge-drinking couples are twice as likely to be involved in physical aggression towards each other, University of Otago research has found.

Professor Jennie Connor of the department of preventive and social medicine in Dunedin said it was the first time the link between partner aggression and drinking has been studied in New Zealand.

Researchers studied all forms of physical aggression, as violence in partnerships commonly escalated from less severe aggression, she said.

The study found if one or both partners had a pattern of heavy drinking episodes - or binge drinking - then physical aggression was more common.

...

They were also more likely to report that their partner had been drinking when physically aggressive towards them and this situation was associated with the highest levels of severity, anger and fear.

"Making changes to the price, availability and promotion of alcohol to reduce the amount of heavy drinking across the whole population will be a good start to reducing the frequency and severity of physical aggression in New Zealand homes,'' Connor said.
The full paper's here. And there's absolutely nothing in the study design that allows for causal inference. The correlation that winks more suggestively at causation is that spouses experiencing violence report that such instances are more frequent when the partner has been drinking heavily. And it's likely that some of these reports will involve violence that would not otherwise have taken place. But other instances of violence could easily be shifts in when the incident takes place: a displacement effect rather than newly induced violence.

Professor Connor's press release suggests policy changes:
“Making changes to the price, availability and promotion of alcohol to reduce the amount of heavy drinking across the whole population will be a good start to reducing the frequency and severity of physical aggression in New Zealand homes.”
It would be nice if she had any evidence of the elasticity of heavy drinking with respect to these policy instruments (hint: for price, it's very low).

HT: ed.co.nz

2 comments:

  1. Are you familiar with the work of Mark Kleiman? Of all the anti-legalization folks, who is the one I most respect by far. He also thinks we (the U.S) don't tax alcohol nearly enough considering its social costs, and also said it's mainly the heavy drinkers he wants to target and that their behavior will be affected more. The book I've read from him is "When Brute Force Fails: How to Have Less Crime and Less Punishment" (I thought it was excellent and everyone should read it), but he recently co-authored a book more relevant to your focus, "Drugs and Drug Policy: What Everyone Needs to Know". He discusses it with the pro-legalization John McWhorter here.

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  2. Book's now on order, thanks TGGP.

    I don't know how the US tax rate compares to policy relevant, external costs. I worry about excise as policy instrument because it imposes harms on moderate drinkers while curtailing harms done by the irresponsible ones where policies like zero blood alcohol limits and ignition interlocks for repeat drink drivers impose costs only on those who impose costs on others and directly target behaviours that cause external harms.

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