The Gateway Theory - Correlation does not prove Causation

The “Gateway Theory” of marijuana prohibition goes like this: marijuana use leads to “hard drug” use, such as cocaine and heroin. Since cocaine and heroin use are “bad”, we must criminalize marijuana to keep our children (and perhaps ourselves) from becoming hard core drug addicts.

The proof of the Gateway Theory is supposed to lie in the statistics that show that cocaine and heroin users in large part started out using marijuana. Since correlation (apparently) proves causation, marijuana use in teenagers and young adults therefore causes “hard drug” use later on.

Like most logical fallacies, when presented artfully, this can be a persuasive rhetorical device: it appears that the proponent of the theory is correct. Cocaine and Heroin users have a very high incidence of marijuana being their first illegal drug of choice. There must be a causal connection.

Let’s ignore for now the refutation that a higher percentage of cocaine and heroin addicts consumed alcohol than marijuana, and we all “know” that alcohol use does not cause cocaine or heroin addiction… (since many readers, like me, are occasional alcohol consumers who have never tried cocaine or heroin)

Let me ask you this: don’t you think the percentage of cocaine and heroin users that drank milk sometime in their lives (before use of the drug) is probably almost 100%?

Correlation does not prove causation. That’s just another logical fallacy brought to you by the Drug Czar.

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Austin Criminal Defense Lawyer - April 12, 2008 8:47 PM
Dallas defense lawyer Robert Guest writes about how the D.A.R.E. program has been a complete waste of taxpayers’ money:By all accounts DARE HAS BEEN A COMPLETE FAILURE. DARE has shown no efficacy in keeping kids from using drugs, alcohol, or...
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Arthur - January 25, 2010 9:48 PM

this becomes pretty vacuous at the end. Do you win a lot of cases?

The reason one would think that "the percentage of cocaine and heroin users that drank milk sometime in their lives...is probably almost 100 percent" is unsurprisingly because the percentage of nearly everyone who drank milk sometime in the lives is probably almost 100 percent.

Jamie - January 26, 2010 2:01 PM

Arthur, I have decided to answer your comment in this post

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