

Teens Beware: Using Marijuana Could Make You Dumber - lutusp
http://www.wired.com/wiredscience/2012/08/marijuana-lowers-iq

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lutusp
The linked study, like most marijuana studies, has no meaningful controls and
therefore represents a correlation, not a cause-effect relationship.

The conclusion drawn from the popular account (i.e. "could make you dumber")
is not supported by the study in any scientific way.

~~~
rm999
>has no meaningful controls

There are two meaningful controls, which combined hint at a causation. The IQ
test from age 13, before many people begin pot use, is a control over who
makes the decision to start smoking weed, and the non-smoker and smoker groups
provide a control over whether pot made people stupider.

So, what factors could cause the study to show the correlation but not be a
direct causation? It would have to be a confounding factor that both makes
people want to smoke and something that causes them to get stupider over time
that isn't the marijuana. That's possible, perhaps some sort of addictive
personality disorder. But I think the simplest explanation is a causation,
there is other evidence that marijuana affects the brains of adolescents.

~~~
lutusp
> There are two meaningful controls ...

No, I meant real, scientific controls. A study with real experimental and
control groups would have groups that the researchers _told_ that they would
smoke, or not smoke, pot. That would make the study prospective, not
retrospective as in this study.

If a study must monitor behavior that the subjects choose for themselves, the
study loses all value, because the result can never be more than an
uncontrolled correlation between A (IQ) and B (the choice to smoke pot) and
any number of possible correlated factors (C) like socioeconomic, genetic, and
other uncontrolled issues.

This is one of the common threads that run through most of these studies,
which is why I linked the article -- it's typical of studies that I've been
reading for about 35 years, and all of which suffer from the same systematic
flaws.

Obviously a real, disciplined study of this topic would assign behaviors in a
double-blind study. But such a study would clearly be unethical, which is why
it has never been conducted.

> So, what factors could cause the study to show the correlation but not be a
> direct causation?

The fact that the subjects make their own decisions, the fact that _there is
no control group_ as that term is understood.

> It would have to be a confounding factor that both makes people want to
> smoke and something that causes them to get stupider over time that isn't
> the marijuana.

Yes, and until we think of a way to study this topic scientifically and
without violating ethical guidelines, we will never know. It could be
socioeconomic, genetic, peer pressure (smart people are geeks, don't you know
that?) or some other factor.

> But I think the simplest explanation is a causation ...

That isn't an explanation unless we study it scientifically, this study
doesn't do that.

This is what I find troubling about psychology studies, studies that involve
monitoring behaviors but with no meaningful controls -- people don't seem to
understand that it isn't science.

> ... there is other evidence that marijuana affects the brains of
> adolescents.

Yes - and all such studies have the property this study has -- no scientific
controls.

This is in no way meant to condone drug use. All I am saying is public policy
is being shaped by something other than science.

~~~
rm999
>If a study must monitor behavior that the subjects choose for themselves, the
study loses all value

You'll almost never find medical studies over long periods of time like this,
and you'll never find a truly causal study on complex human behavior; there
literally is no medical research that can properly do this. This is an
epidemiological study, and these kinds of studies DO have value and certainly
are scientific. This is the field that "proved" cigarettes are bad for us and
that red meat increases the chances of heart disease.

I agree with you that a causal result would be great, but I think we both
agree it's not possible for something like this. My point is that they make a
very convincing case that shouldn't be dismissed so easily - correlations
should be considered for what they are, not thrown out without thought. Your
principled view on this works for some sciences but is too conservative for
the kinds of things epidemiology studies.

~~~
lutusp
>> If a study must monitor behavior that the subjects choose for themselves,
the study loses all value

> You'll almost never find medical studies over long periods of time like
> this, and you'll never find a truly causal study on complex human behavior;
> there literally is no medical research that can properly do this.

Yes, true. This is why decent medical results come from animal studies, and
extrapolating such studies to humans is fraught with difficulties.

> This is the field that "proved" cigarettes are bad for us and that red meat
> increases the chances of heart disease.

Yes -- but using animal models, not human ones! Do you want to argue that
researchers forced people to smoke cigarettes, or not, to control the outcome?
That never happened.

> I agree with you that a causal result would be great, but I think we both
> agree it's not possible for something like this.

"Not possible" cannot be used as an justification to erode scientific
standards.

> My point is that they make a very convincing case that shouldn't be
> dismissed so easily

They do nothing of the kind. The flaws are obvious and fatal to any useful
conclusion. The explanation that a person chooses to smoke pot, and chooses to
avoid intellectually stimulating activities, is much more likely than the
conclusion that pot in and of itself reduces IQ, especially absent a proposed,
testable mechanism.

Obviously if I designed a study that (a) forced a group to smoke pot, and (b)
forced the same individuals to think harder within an intellectually enriching
environment, I would get a result that contradicted this one. But it would be
unethical to conduct such a study.

I cannot stress this enough -- this is junk science, and public policy is
being steered by junk science, by people pretending to be scientists,
pretending to be conducting objective science.

> Your principled view on this works for some sciences but is too conservative
> for the kinds of things epidemiology studies.

"It's too difficult" can never be used as an excuse in defense of sloppy
science. Especially in the presence of a public that cannot distinguish
between sterling and junk science.

All that remains is for the public to become aware how sloppy science is
steering public policy, and I need to add that studies that come to the
opposite conclusion (and they exist) are rarely published. The reason? "It's
sloppy science."

Again, bottom line, none of this is meant to condone or encourage drug use --
there's no science to support that behavior either.

~~~
rm999
I realize that epidemiology can be sloppy science, but it's the only way we
can even hope to tackle immensely important questions like this. It shouldn't
be cast aside because it fails to hold up to impossible standards. According
to your reasoning the vast majority of convincing evidence that cigarettes are
bad for you is junk science (sorry to reuse that example but it's a very
effective one).

Epidemiology is not an answer, it's part of an exploration of a question. This
study is one of possibly many future studies that will attempt to etch away at
the null hypothesis "there is no relationship between intelligence and smoking
marijuana before adulthood". One day ten other studies like it may provide a
more convincing story, or may disprove the idea altogether. Until then, this
is probably the best research on the question yet. It is what will help get
scientists further funding on the topic. And that's why it's important.

~~~
lutusp
> I realize that epidemiology can be sloppy science, but it's the only way we
> can even hope to tackle immensely important questions like this.

First, that's false -- straight-up false. We can violate ethical guidelines
and get terrific, reliable science. All we have to do is abandon our
principles, and victimize innocent subjects. Example the Alabama Syphilis
study:

<http://www.dartmouth.edu/~thabif/newfiles/tuskee.html>

The above is a despicable example of subject treatment, but it falsifies your
claim.

Meanwhile, without abandoning our principles, we can use animal models, as is
done with many kinds of study -- heart disease, cancer and many others.

> This study is one of possibly many future studies that will attempt to etch
> away at the null hypothesis "there is no relationship between intelligence
> and smoking marijuana before adulthood".

The study under discussion is a sham masquerading as science, it has no
scientific value, the design is so poor that no reliable conclusion can be
drawn from it. The level of control for confounding factors is nonexistent.
Apart from that central design flaw, both the subjects and the experimenters
know who the pot smokers were. It's a joke pretending to be science, and
abandons every recognized experimental discipline.

The study certainly doesn't "etch away" at the null hypothesis, because there
are too many pedestrian explanations for the outcome that aren't even in the
thinking of the experimenters.

> One day ten other studies like it may provide a more convincing story, or
> may disprove the idea altogether.

Disproof is also impossible with such a sloppy study design. I can't believe
what you're saying.

> Until then, this is probably the best research on the question yet.

Or the worst, and both claims can be true at once. Your remark reminds me of a
Woody Allen joke. His girlfriend says, "But sex without love is an empty
experience!" Allen replies, "Yes, but as empty experiences go, it's one of the
best!" As meaningless science goes, this study is one of the best.

As I said earlier, I've been reading such studies for about 35 years, and (a)
they all suffer from fatal design flaws, and (b) they always support the
prejudices of the granting agencies and/or those of the experimenters. Also,
important, studies that come to the opposite conclusion, or that don't come to
a clear conclusion, tend not to be published.

> It is what will help get scientists further funding on the topic. And that's
> why it's important.

More bad science is important? I ask you to think about what you're saying.
This study is trash masquerading as science. Anyone can design and carry out
an equally sloppy study (and psychologists do this all the time) that comes to
the opposite conclusion, through the simple expedient of ignoring the many
confounding factors inherent in retrospective studies that don't have a
control group or the kind of experimental discipline that can lead to reliable
scientific conclusions.

This is not science, it is psychological science.

~~~
rm999
I guess we've gotten in a circle of "this is bad science"-> "no it's not".
While I disagree with you, I enjoyed debating it with you.

