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by Peter Moskos

March 1, 2011

Cannabis use 'raises psychosis risk'

Sez a study reported in the BBC.

8 comments:

Anonymous said...

"It found that cannabis use "significantly" increased the risk of psychotic symptoms, even when other factors such as socio-economic status, use of different drugs and other psychiatric conditions were taken into account."

I am very skeptical of this. Even if this is true, does this justify prohbition of marijuana? Use of tobacco obviously increases the risk of cancer. Shall we ban tobacco and imprison users? Of course not! Alchol use can lead to aggressive behavior and, eventually, liver problems. Should we ban that? Oh yeah, we tried that.

Dave H- il

PCM said...

I couldn't agree more.

No, it certainly doesn't support prohibition. But being "fair and balanced," I thought I'd mention the article. I would certainly have mentioned it if it said the opposite!

suz said...

So, what's the statistical definition of "significant?"

PCM said...

Generally a 19 in 20 chance that the results are not simply due to random luck.

In the statistical world, somewhat strangely, "significance" doesn't have to do with the size of the increased chance. You could have a potentially large chance that isn't "significant" and a small chance that is.

suz said...

Thanks for the clarification.

"They excluded anyone who reported cannabis use or pre-existing psychotic symptoms at the start of the study..." I wonder if there were pre-existing psychotic symptoms that were mild enough to go unnoticed, and I wondered if and how that was measured. Based on anecdotal evidence from people I have known, I wouldn't be surprised to find that cannabis may aggravate psychoses. There is a correlation, but figuring out if it's cause-and-effect would take some pretty thorough control measures.

PCM said...

Without knowing more, I would guess you are 100% correct. I would go a step further and say perhaps the initially unmeasured psychosis is then correlated with a desire to get high, or a lack of ability to manage a mild recreational drug habit.

I simply know too many people non-psychotic pot smokers to think this "increased" risk is anything to worry about.

It's such a basic problem of quantitative research: a false faith in the validity and reliability of measurements (and also non-random error). It screws up everything that comes afterward, too often making all those fancy stats and correlations all-but meaningless. But because there's less than a 5 percent chance variation in the numbers is simply due to random chance, we're expected to believe everything.

Marc said...

I don't think I've read one of these studies, explored the methodology and thought that they were remotely close to a "slam dunk".

Anonymous said...

I dont know if that is true? I never heard any studies about that,cannabis seems to be more potent NOW then it ws in the 70's so the textbooks say, but because they use more chemicals or whatever it is they use to grow cannabis causes"significantly" increased the risk of psychotic symptoms, I disagree