This is your media on “drugs”
You may believe, Gentle Reader, that this blog is entirely negative towards stories about drugs. That’s because the relationship between numbers and conclusions is often seriously overstated, if not completely made up. An illustrative example is today’s story in the Herald. Apart from the statistics, this is a reasonable story. It has information based on actual measurements, and comments from two people who know what they are talking about, one of whom is independent of the data source. Unfortunately, the story is let down by the statistics.
Police and ESR actually grew some cannabis from high-quality seized material, and measured the THC concentration, comparing the results to when they did the same exercise in 1996. This is potentially a fair comparison, although the sample size is small. Unfortunately, they reported the mean (6%) from 1996 and the range (4.35%-25.3%) from the recent study, so the conclusion in the headline “Dope quadruples in THC strength” is not actually supported by the article. The growing study wasn’t even that recent — it ran from 2004 to 2006 — making the support for the headline even more dubious. It’s not that the headline is intrinsically improbable, if growing has largely moved indoors and changed to modern strains, but we aren’t given any evidence.
The comment by Detective Sergeant Miller that “We are not seeing poor quality cannabis. It’s all good quality” is interesting. In the US, according to Stanford expert Keith Humphreys, that isn’t the case: there is a lot of cheap, low-grade cannabis, and a smaller amount of boutique high-grade stuff.
Robin Ross Bell, from the Drug Foundation, makes the important point that we don’t actually know if higher concentrations of THC are more dangerous — people may just use less when it’s strong. This is especially true since smoking gives immediate feedback on dose, and we do know that tobacco smokers get about the same nicotine dose from varying nicotine concentrations in cigarettes. It’s encouraging that there is actual research being done on this topic.
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 »
Check Dan Gardner’s excellent Canadian piece debunking some of the “This isn’t the pot you remember from your youth” argument.
http://www.ottawacitizen.com/Gardner+myth+potent/5704851/story.html
13 years ago
Yes, and we’ve done that story, and Ben Goldacre has done it, and so have many others.
This is slightly different since it is would be a useful comparison if they’d reported the data properly.
13 years ago
Agreed. But there’s likely a reason the data weren’t reported properly…
13 years ago
It is interesting that the latest estimate is based on 3 cycles of six (6) plants only/ I’m not sure what a cycle is.
We could look at the problem from a different point of view. How easy would it be to increase THC content in Cannabis by breeding? Estimates of heritability for that trait are highly variable, with some low values (0.15) to high (0.75). Even with high values it would be hard to increase THC contents fourfold. There is always the possibility of bringing new genetic material to the country, but it sounds very complicated for an illegal (and not so high value) crop.
13 years ago
Luis,
It’s not just breeding. There is also (in principle) almost perfect control of growing conditions. Given both of these, I don’t see why it should be impossible to consistently achieve concentrations that have been intermittently achieved in seized material for decades. The main obstacle is that it might take too much skill or effort to be worthwhile.
If you want better information on what’s possible, I’d try looking for data from the quasi-legal Dutch industry.
13 years ago
Hi Thomas
The name is ROSS Bell, not Robin.
Cheers
Ross
13 years ago
Aargh. Sorry. Fixed now.
13 years ago