July 23, 2013

Legal high bans and crime

From Scoop, in a press release on the legal-highs bill by Manurewa Local Board member Toa Greening

Ireland led the way by prohibiting all non-prescribed psychoactive substances back in 2010. This resulted in an immediate reduction in related psychoactive substance health issues and crime.

Irish data on recorded crimes is available throught the Ireland Official Statistics portal, Statcentral.ie.  This graph shows quarterly data since 2004 for the main crime categories (the heavy blue line is drug offenses, and the vertical line is when the ban came into force)



I don’t see any dramatic effects of the ban on any category of crime.


Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »


  • avatar
    Andrew Veale

    An interesting one would be the trends on crime in Portugal which decriminalized all drugs – I’ve seen it quoted that crime significantly decreased there, though have not seen the raw data. Some stats are mentioned here: http://www.time.com/time/health/article/0,8599,1893946,00.html

    4 years ago

  • avatar

    The dark blue line is decreasing (yes, that started happening a bit before the horizontal line). The logarithmic scale of the y-axis is also makes the graph very awkward to read.

    While there are many other effects in play it looks to me like this graph does slightly support the claim. So I don’t understand this post.

    4 years ago

    • avatar
      Thomas Lumley

      The fact that the line started decreasing before the ban makes it unlikely that the ban is responsible.

      I don’t think the log scale is a problem — the graph is actually harder to read on a linear scale, that’s why I used the log scale

      4 years ago

  • avatar

    “The fact that the line started decreasing before the ban makes it unlikely that the ban is responsible.”

    For starting the decline, sure. It might be playing a role in the continuing downward trend, though. To really dismiss a comment like this one I’d have wanted to see a really flat line or one that rises :)

    4 years ago