Bayesian Updating: what we can learn from drug law reform in Portugal

I’ve recently been preparing the part of my course devoted to knowing when to change your mind, and central to my argument is the idea of Bayesian Updating: modifying the strength of your beliefs, and thus altering any actions or behaviours that might arise from those beliefs, in response to new information that you receive that is relevant to those beliefs.

An opinion piece at the Washington Post site by Christopher Ingraham, regarding the success of last decade’s reforms to drug laws in Portugal, seems relevant in this regard. I’ll quote some of the appropriate passages:

Portugal decriminalized the use of all drugs in 2001. Weed, cocaine, heroin, you name it — Portugal decided to treat possession and use of small quantities of these drugs as a public health issue, not a criminal one. The drugs were still illegal, of course. But now getting caught with them meant a small fine and maybe a referral to a treatment program — not jail time and a criminal record …

The prevalence of past-year and past-month drug use among young adults has fallen since 2001, according to statistics compiled by the Transform Drug Policy Foundation, which advocates on behalf of ending the war on drugs. Overall adult use is down slightly too. And new HIV cases among drug users are way down.

Now, numbers just released from the European Monitoring Centre for Drugs and Drug Addiction paint an even more vivid picture of life under decriminalization: drug overdose deaths in Portugal are the second-lowest in the European Union.

Among Portuguese adults, there are 3 drug overdose deaths for every 1,000,000 citizens. Comparable numbers in other countries range from 10.2 per million in the Netherlands to 44.6 per million in the U.K., all the way up to 126.8 per million in Estonia. The E.U. average is 17.3 per million.

Perhaps more significantly, the report notes that the use of “legal highs” — like so-called “synthetic” marijuana, “bath salts” and the like — is lower in Portugal than in any of the other countries for which reliable data exists. This makes a lot of intuitive sense: why bother with fake weed or dangerous designer drugs when you can get the real stuff? This is arguably a positive development for public health in the sense that many of the designer drugs that people develop to skirt existing drug laws have terrible and often deadly side effects.

This is great news, and it indicates that decriminalisation of drug use is associated with lower rates of harm arising from that usage than in countries where usage is criminalized and thus driven underground and into an unregulated black market controlled by the most vicious and unscrupulous thugs.

But if we want information on success, we need to see how harm arising from drug usage has changed since the introduction of the reforms. Is there any such information?

Still, it’s very clear that decriminalization hasn’t had the severe consequences that its opponents predicted. As the Transform Drug Policy Institute says in its analysis of Portugal’s drug laws, “The reality is that Portugal’s drug situation has improved significantly in several key areas. Most notably, HIV infections and drug-related deaths have decreased, while the dramatic rise in use feared by some has failed to materialise.”

Prima facie, that seems like unambiguously good news! More grist to our mill. However, we still have to be careful that we have correctly identified the cause of the improvement as being decriminalization, rather than some other cause – we don’t want to be like all those other people, and commit the FAC, after all. Does the article have anything to say about this?

Drug use and drug deaths are complicated phenomena. They have many underlying causes. Portugal’s low death rate can’t be attributable solely to decriminalization. As Dr. Joao Goulao, the architect of the country’s decriminalization policy, has said, “it’s very difficult to identify a causal link between decriminalization by itself and the positive tendencies we have seen.”

As state legislatures debate with issues like marijuana legalization and decriminalization in the coming years, Portugal’s 15-year experience may be informative.

Sound analysis. What we need is a study which controls for all those other causes, and looks for changes in the levels of harm caused by drug usage, and possibly also drug usage, per some population indicator (per capita, or per 1,000 people), and concentrating on usage in higher-risk age groups (no use looking at usage among late-middle-aged women, for example, when the groups at risk are young people).

As it is, the information presented in the opinion piece should be sufficient to encourage the authorities in this country to start re-thinking old beliefs about drugs and drug use, and current approaches to controlling drug usage and to harm minimization. A further study which corroborated the prima facie findings should be sufficiently powerful to encourage a ‘rethink’ or ‘fresh look’ among many of those who think that the current approach works.

Bayesian Updating for the win!


About Stebbing Heuer

A person interested in exploring human perception, reasoning, judgement and deciding, and in promoting clear, effective thinking and the making of good decisions.
This entry was posted in Mind-sets and Logic-Bubbles, Reasoning and tagged , . Bookmark the permalink.

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