DUI arrests decrease after state monopoly on liquor sales ends

This is another example where, if you lack analytic skills, you will jump to the wrong conclusions. This news article was published in MyNorthWest. It's about the new law that went into effect a year ago in WA, allowing grocery stores to sell hard liquor. Here we provide 16 reasons that could explain this paradox. You might even come up with additional reasons.

There is a glitch in the data collection process, the data is wrong.
The article is posted by someone with a conflict of interest, promoting a specific point of view. It is politically motivated. It's just a bold lie.
There were fewer arrests because the state laid-off many policemen.
What about other crimes? Did alcohol-related domestic violence increase?
Is it part of a general downward trend? Without the new law, the decline would have been even more spectacular?
Lack of statistical significance.
More strict penalties deterring drinkers.
There is more drinking by older people. As they die, DUI arrests decline. Or population of drinkers is decreasing, even though the population in general is increasing, driven by Chinese and Indian immigration - people who drink much less.
Is the decrease in DUI arrests for WA residents, or for non-residents as well?
It should have no effect because anyone could still buy alcohol (except hard liquor) anywhere in any grocery store in WA, before the new law.
People do drink more, but are more careful or get too drunk to drive, when switching from beer to hard liquor.
Prices (maybe because of increased taxes) have increased, creating a dent in alcohol consumption. Although alcohol and tobacco are known for their absence of price elasticity.
People drive shorter distances to get their hard liquor now, so arrests among hard liquor drinkers have decreased. Or they can drive to get their liquor when they are sober (before, it was just between 8 am and 5 pm at a state store).
Is the decline widespread among all drinkers, or only among hard liquor drinkers?
Maybe people are driving less, in general - both drinkers and non-drinkers. Maybe because gas is too expensive.
A far better metric to assess the impact of the new law is the total consumption of alcohol (especially hard liquor) by WA residents

On a different note, how would you measure the impact of the following wine fraud: you go to a restaurant, order a $20 glass of wine, get offered a $10 wine glass and charged $20. Some claim that most Americans would not notice the difference. It happened to me once with a glass of champagne (substituting good champagne with something totally undrinkable), but it could have been an accident.

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Comment by Phillip Burger on July 24, 2013 at 7:36am: Here’s the basis for my skepticism and maybe a way out of the problem.

With the suite of techniques currently available, we would use either a supervised or unsupervised algorithm. Forget supervised. There is one data point, WA state, and we can’t assign a measure. We have a problem even trying to classify this one outcome (the whole point). At most, we would ever have 50 data points, to train on. But, what is the test and what is the test data. Supervised is out. Maybe an unsupervised learning model? Dimensionality reduction. We lack a measure and there’s limited data.

Let’s classify some outcomes. My next idea would be to propose a literature review and secondary data analysis using results from other states over maybe the last 40 years of liberalizing access to alcohol. Classify each. We now have the basis of a training set.

Comment by Phillip Burger on July 23, 2013 at 3:40pm: The first thing I thought about when reading the article is causality vs. correlation.

I don’t think the problem is answerable with any confidence. Vince, as usual, you list a whole host of good questions that could be important.

But, we have to make progress somehow. In this case, I’d define my costs differently, I’d define it as public safety. I’d scope it in a way that I would have some confidence in my methodology and data. Underage drinking would be good. The null hypothesis: underage drinking remained unchanged. I think answering this question is doable. And, importantly, it matters.

I’m skeptical that models will be invented that take into account the reasons for the paradox while establishing causality.

Comment by joe martins on July 21, 2013 at 11:30am: Vincent, re wine/champagne, it's only fraud if it's mislabeled.

Taste is subjective. Run an experiment with your friends. Buy some $5, $50 and $100+ wines and pour them into identical glasses. No hints of any sort. You'll find that much of the time even those who purport to be oenophiles can't tell the difference between popular cheap wines and the more expensive varieties.

Re: the rest of the article, I'm not sure anyone could come up with any meaningful connection between that law and its effect on DUI. Some relationships remain beyond the reach of even the best models...at least for the foreseeable future.

Comment by Vincent Granville on July 20, 2013 at 12:48pm: How would you get the right data and the right methodology, to assess the impact of the new law? For the state of WA, the question is: did we reduce costs related to alcohol consumption (by increasing tax revenue from alcohol sales, laying off state-store employees, modest or no increase in alcohol-related crime, etc.)