A reader may ask how this result could arise by something other than a cause-effect relationship? Maybe people find themselves under peer pressure to (a) smoke pot, and (b) reject the value of scholarly activities. Someone might answer that IQ is predetermined, that it doesn't have any environmental component. But that idea has been falsified in animal studies, studies that show the development of new brain cells in animals that live in stimulating environments.
There are any number of factors that might lead an individual to simultaneously choose to smoke pot and avoid activities that might improve his IQ -- socioeconomic, genetic, and so forth. The only way to control for these things is to design a truly scientific study that tells experimental subjects whether they will smoke pot, rather than asking whether they do. But such a study would be unethical, which is why there's no science in this field of study.
This study is much like thousands of studies I've read over about 35 years, and all of them suffer from the same flaw -- they aren't science. Correlation is not causation.
The linked study represents psychology at work -- science in name only.
One of the things that often concerns me about Silicon Valley in recent years has been the trend of many startups where pot smoking is part of the established culture of the company. I don't think it's a majority, but it's certainly more than I'd realized previously and it certainly seems to be a more recent trend.
I'm not a vehement prohibitionist by any means. However, I've been burned by a co-founder showing up stoned to a key meeting with an investor who'd committed a 6-figure sum out of his own pocket to get the company to where it was. That was a problem.
Maybe it's just me aging - I am not a big drinker nowadays, after going through the same college years everyone else did where drinking was involved in so much social activity - but over the years I've arrived at the belief that much of the time wasted stoned, by folks convinced this is making them more creative, is time that could be put to better use.
Feel free to do what you want to do, sure. But reminding people that there are negative consequences is never a bad thing.
I have primarily two objections.
First, the article fails to rule out:
- The possibility that people who start smoking pot prior to the age of eighteen and continue to smoke are just generally likely to be the type of person who might get stupider with age anyway.
Second the argument fails to consider:
- That an alternative explanation could explain the facts of the study equally well: namely, that it's not the age at which one begins to smoke which causes this IQ decrease but rather that it is the sustained use of marijuana which is actually damaging.
http://dunedinstudy.otago.ac.nz/news/dunedin-study-theme-lea...
that has produced some other path-breaking research papers on child development. In other words, while this study is not the last word on the subject of the headline here, it is conducted by researchers who are used to scholarly controversy and having other researchers check their work. So I'll be curious to check the underlying journal article (for which I have yet to see a citation in any of the several news reports about this today).
Repeating a study with no meaningful controls ignores the same factors, and doesn't change the outcome -- until a prospective double-blind study is carried out, we don't have anything except a correlation, and a correlation is not a cause-effect relationship.
Here's a perfectly plausible explanation that the research ignores -- individual who choose to smoke pot are under peer pressure to avoid intellectually stimulating activities. The latter factor causes their measured IQ to drop, compared to others who embrace a lifestyle with more intelligence-enhancing activities.
Is that possible -- can an individual improve his IQ by choice of activities? Yes, according to animal studies that do have meaningful controls -- animals that are placed in stimulating environments grow new brain cells:
http://www.pbs.org/saf/1101/segments/1101-2.htm
It doesn't matter how many times such drug use studies are conducted or replicated -- if they have the same systematic flaws, repetition doesn't increase their value.
The gold standard for this class of study is a double-blind, retrospective study, and such a study has never been conducted for ethical reasons.
This study is typical "psychological science" -- science in name only.
