What happens to your mind when you smoke some bad reporting

Of course, we all know that the bizarre propaganda item I posted yesterday (Smoking just one cannabis joint raises danger of mental illness by 40%) is inflammatory nonsense.
There wasn’t an ounce of legitimate reporting in that story, and just about every media source that has picked it up has been infected by junk reporting as well (even though many of them, later on in the piece, indicate that there is no real evidence of any causation at all).

“The researchers said they couldn‰t prove that marijuana use itself increases the risk of psychosis, a category of several disorders with schizophrenia being the most commonly known.
There could be something else about marijuana users, ‹like their tendency to use other drugs or certain personality traits, that could be causing the psychoses,Š Zammit said.”

Daksya gave it to us straight in comments:

To clarify:

1. This isn’t an original study. It’s a review or more precisely, a meta-analysis of existing studies. Regarding psychosis, 7 longitudinal observational studies are pooled to generate the odds ratio of 1.41 i.e. the 40% increase in risk.
2. The 7 studies did not all measure the same thing. Some looked for the presence of any psychotic symptom; others looked for presence of symptoms necessary to diagnose schizophrenia (and schizophreniform disorder in one study). So, one may infer about odds of experiencing psychotic symptoms but not the odds for schizophrenia or any other clinical diagnosis of a disorder.
3. Continuing the usual mathematical ignorance displayed in journalism, the analysis does NOT suggest that smoking cannabis even once or ‘infrequently’ increases odds of schizophrenia by 40%. First, the study does not report on odds of schizophrenia. But relevantly, the 40% increase is for the whole group of those who ever used cannabis compared to those who never used cannabis viz. the former contains all users i.e. experimenters, occasional smokers, regulars and dependents. The risk specific to experimenters or infrequent users is not reported.
   To illustrate the mathematical point, take two groups of 1000 people, same in all relevant ways, except for cannabis use history. In Group A, we have 1000 people with a history of 0 joints i.e. non-users. Let the baseline rate of psychosis be 4% or 40 cases out of 1000. So, in Group B, consisting of 1000 people, all with some history of cannabis use, there will be 64 56 cases of psychosis out of 1000. But these 64 56 cases aren’t spread out uniformly over all categories of cannabis users (just once, weekly, daily..etc). As the analysis authors state, there is a dose-response effect. So, in Group B, which includes all sorts of users, the heavy users will have a disproportionate higher share of the cases, and the other groups, consequently, disproportionately lower. So, the odds for the other users have to be sufficiently lower, so as to “balance” the 2.09 odds for heavy users, in order to obtain the average of 1.41 for the whole group. Just how much is that, depends on the internal prevalence of each category within Group B.

Of course, that’s too much actual science for most reporting, and it doesn’t provide anything flashy and scary, so they go with nonsense.
And naturally, there are idiots out there who want to believe it.
Here’s one that I found who was particularly amusing at Blogs 4 Brownback. This guy lays out the stuff from the Daily Mail as gospel with his added comments…

One joint = brain damage. Don‰t stick that in your pipe and smoke it or you‰ll go crazy. It‰s been proven. […]
There is much more in the article that drug apologists should read, including a Rogue‰s Gallery of violent criminals who just got a little high, only to launch into horrific violent crimes. […]
We really need to get serious about the war on dangerous drugs. We need more prisons, more prosecutors and stronger sentences with teeth that bite. It‰s time to send a message to casual drug users and dope peddlers. If you use or sell drugs you will do time. Hard time. No exceptions. Caught, prosecuted, punished. And no leniency. Dope fiends need to be locked up, not coddled.
Your brain is not a toy. So don‰t stick things in your nose or ears and try to play with it. Any questions?
I trust that a President Sam Brownback would do the right thing and put us on a path to ultimately and with finality at long last win the drug war. It‰s the right thing to do.

That was funny enough, but then his first commenter — a Mrs. T.D. Gaines-Crockett wrote:

I believe that pot smoking is just another symptom of Liberalism. Once someone goes out of his or her way to accept the immoral and unholy as the norm, they just open the door to drug abuse and criminal activity. Anyone who is smoking that stuff might as well have a loaded gun in their mouth; it is just as dangerous.
Jesus, come quick! America is killing itself.

Reading the comments is a surreal experience in itself (including a moron who basically duplicated the brownie-eating-cop-calling-911 stunt), although finally one or two sane adults step in to inject some reality into the discussion.
It’s a minor site and probably not worth our attention, but what is interesting is that even there people finally started to question and correct the nonsense, and that’s worth noting.
People are getting better informed. We’re helping to do that. And every day, it’s getting hard to pawn off that stale reefer madness. Oh, sure, the tabloids eat it up, and the politicians love it, but the ordinary, intelligent, informed citizen knows better. They’re smart enough to think “where are the bodies? where are the millions of slobbering psychotics? why do prohibitionists act crazier than potheads?”
Update: Mark Kleiman responds to the hysteria nicely:

If cannabis caused schizophrenia, we ought to see rates of schizophrenia correlated with rates of cannabis use, both across countries and over time. […]
So far, there is exactly zero cross-section or cohort evidence showing a link between cannabis and schizophrenia.[…]
But the null hypothesis doesn’t make headlines, so I doubt we’ll hear much about cohort effects in the press.

2nd Update: Ben Goldacre in The Guardian straightens out the British tabloids.

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%”. […]
But what’s really important, of course, is what you do with this data. Firstly, you can mispresent it, and scare people. Obviously it feels great to be so self-righteous, but people will stop taking you seriously. After all, you’re talking to a population of young people who have worked out that you routinely exaggerate the dangers of drugs, not least of all with the ridiculous “modern cannabis is 25 times stronger” fabrication so beloved by the media and politicians.
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. We’re talking about communities, and markets, with people in them, after all: not molecules and neuroreceptors.