Monday, July 30, 2007

If it's drug hysteria, it must be Friday.

We can't let the party really get started on Fridays without a press release from the Ministry of Buzzkill, So here's a thought: let's see what they have to say.

Experts dismiss case for cannabis reclassification | Special reports | Guardian Unlimited
Drug experts today said there was still insufficient evidence to reclassify cannabis, after a report suggested the drug could increase the risk of schizophrenia by at least 40%.
The Labour MP Brian Iddon and Professor Robin Murray, of the Institute of Psychiatry, said there would be no benefit gained by restoring cannabis to a class B drug.

I would consider that to be a self-evident point. Still, this idea of a lot of people developing schizophrenia because of dope seems like a nasty point. How bad is it anyway?
Prof Murray said: "Individuals who - perhaps with some mild predisposition - would not otherwise have developed schizophrenia will do so because of taking cannabis. It's a bit like how people with only a minimal predisposition to diabetes will develop it if they eat too much."

I guess it's time to make Galaxy bars a class B drug.
Net result:
The MP, who is also a member of the science and technology select committee, said there was a danger of criminalising "hundreds of thousands of young people" if the status of the drug was changed.

"If Gordon Brown changes the class of the drug, it won't be evidence-based but for political reasons," he said.

"Since we reduced the classification of cannabis from B to C the usage is going down, so what's the point of muddying the debate again by this yo-yo political policy?"

For some reason no-one seems to be that impressed with this study's conclusions. Why is that?
The study, which is an analysis of previous research, estimated that 14% of 15-34-year-olds currently suffering from schizophrenia were ill because they smoked cannabis.
[emphasis added]
Ah, meta-studies. Take the results of a dozen badly done studies and average the results on the presumption that the total of bad data equals good data. These tend to be the same people who don't seem to understand why you can't average averages and get a result.
Further question: is anyone else noticing that one little key phrase in the article.

Bad Science » Blah blah cannabis blah blah blah
You know when cannabis hits the news you’re in for a bit of fun, and this week’s story about cannabis causing psychosis was no exception. The paper was a systematic review and then a “meta-analysis” of the data which has already been collected, looking at whether people who smoke cannabis are subsequently more likely to have symptoms of “psychosis” or diagnoses of schizophrenia. Meta-analysis is, simply, where you gather together all of the numbers from all the studies you can find into one big spreadsheet, and do one big calculation on all of them at once, to get the most statistically powerful result possible.

Yes you do, assuming good content. Much like in logic, if you have false premises you have false conclusions. Meta analysis isn't worthless, any more than historiography is worthless, but you do have to be have to be careful with the results. Goldacre continues:
Now I don’t like to carp, but it’s interesting that the
Daily Mail got even these basics wrong, under their headline
“Smoking just one cannabis joint raises danger of mental illness
by 40%”. Firstly “the researchers, from four British
universities, analysed the results of 35 studies into cannabis use from
around the world. This suggested that trying cannabis only once was
enough to raise the risk of schizophrenia by 41%.”

Oops. That wasn't careful, was it. No it wasn't, thanks for asking.
And craziest of all is the fantasy that reclassifying cannabis will
stop six million people smoking it, and so eradicate those 800 extra
cases of psychosis. If anything, for all drugs, increased prohibition
may create market conditions where more concentrated and dangerous
forms are more commercially viable.
And that may also be the point. I like to think back to the 1930s and how prohibition cured all alcoholism. Ahh, good times.

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