Portugal: Lessons on Drugs and Statisitics

The Liberal Conspiracy has interesting article on the drug decriminalisation in Portugal. Two highlights for me.

The opening paragraph:

The right predicted Bad Things: Drug use would explode, tourists would travel from far and wide to get high on the streets of Lisbon, law and order would collapse, and people would start riding around in modified cars and fighting in Thunderdomes

This just made me laugh:)

Now what made me cringe was the stats from a Cato paper looking at Portugal:

Prevalence rates for the 15–24 age group have increased only very slightly, whereas the rates for the critical 15–19 age group—critical because such a substantial number of young citizens begin drug usage during these years—have actually decreased in absolute terms since decriminalization.

Perhaps most strikingly, while prevalence rates for the period from 1999 to 2005, for the 16–18 age group, increased somewhat for cannabis (9.4 to 15.1 percent) and for drugs generally (12.3 to 17.7 percent), the prevalence rate decreased during that same period for heroin (2.5 to 1.8 percent), the substance that Portuguese drug officials believed was far and away the most socially destructive.

If you feel confused after reading that paragraph don’t worry. The Liberal Conspiracy’s description of this passage hit the  spot for me:

What the above basically demonstrates is that if you cherry-pick the right start years and end years for an age-group, you can get almost any result you want

Lies, damned lies and statistics….

  • Note: This is the initial post I read:


    Which lead me to this post:


    Which lead me to the post I emailed you 😀

  • Hi, I’m glad you liked my piece for LibCon (my own blog is at layscience.net, but I also write for them once a week).

    It’s funny, that quote was pretty much the point where I decided I didn’t have much faith in the Cato analysis…

  • I’m confused: why are we measuring drug problems using prevalence of drug usage? I imagine that the problems come not from widespread usage but from individual overuse. I’m not really convinced of anything by an analysis that equates prevalence with harm so I think the problems with that quote run even deeper than you’ve suggested.