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Sheriff Stanek’s marijuana comments confuse correlation and causation

REUTERS/Andres Stapff
The relationship between marijuana and violent crime is still very much up in the air, scientifically speaking.

In a Sunday commentary in the Star Tribune and later in an interview on Minnesota Public Radio, Hennepin County Sheriff Rich Stanek made the classic mistake this week of confusing correlation with causation.

Sheriff Rich Stanek

While arguing against the legalization of marijuana, Stanek noted that “approximately 54 percent of males arrested for violent crime test positive for marijuana in Hennepin County.”

That observation, he stressed in both the commentary and the interview, points to “a direct connection between marijuana and violent crime.”

Well, it may show a correlation between the two, but it doesn’t show a causation. Just because half of the men arrested for violent crime in Hennepin County test positive for cannabis (a drug that can apparently linger in the body days or even weeks after it is used, by the way), doesn’t mean that the cannabis caused their criminal activity.

It could also mean that men who commit violent crimes are, for whatever reason, more likely to smoke marijuana.

“A” may be associated with “B.” But that doesn’t mean “A” caused “B.”

Research is inconclusive

Actually, the relationship between marijuana and violent crime is still very much up in the air, scientifically speaking. That’s the clear message from a long but painstakingly thorough paper on the topic that was published in the Journal of Drug Education in 2011.

In the paper, Southern Utah University sociologist Michael Ostrowky reviews the leading theories and key research on the relationship between marijuana use and aggressive/violent behavior.

He concludes that the findings are all over the place and thus inconclusive.

“Taken together, the results of some studies suggest that marijuana use and violence are positively associated, some research has found no association, and other studies even reveal that marijuana use can reduce aggressive behavior,” he writes. “These conflicting findings are not overly surprising, considering that marijuana has been classified at different times by different investigators as a depressant, a stimulant, a hallucinogen, and a narcotic.”

Dueling studies

Here’s a sampling of some of the conflicting studies discussed by Ostrowsky in his article, starting with those that found no significant relationship between marijuana use and violent behavior:

  • Utilizing longitudinal data from a community cohort of African Americans, Green, Doherty, Stuart, and Ensminger (2010) did not find an association between heavy adolescent marijuana use and violent crime.
  • Pedersen and Skardhamar (2010) examined data from the Young in Norway Longitudinal Study and found no evidence that use of cannabis is associated with an increased risk of subsequent non-drug-specific criminal charges, such as violence.
  • In a qualitative, cross-sectional study of Canadian clients attending substance abuse treatment programs, Erickson, Macdonald, and Hathaway (2009) discovered that alcohol, cocaine, and crack were the substances most implicated in the client’s descriptions of their drug-related violent incidents. In fact, the authors report “it is noteworthy how seldom cannabis was mentioned.”
  • Using cross-sectional internet survey data, Denson and Earleywine (2008) found no relationship between marijuana use and aggression once other factors were taken into account. In fact their data suggest that marijuana use is not related to aggressive behavior even among frequent, long-time users.

Here are Ostrowsky’s summaries of a couple of the studies that found marijuana use was associated with decreased aggression or that reported mixed findings:

  • In a four-wave analysis, White and Hansell (1998) observed that heavier marijuana use in early to mid-adolescence predicted decreased aggressive behavior in later adolescence and young adulthood.
  • In a cross-sectional analysis, Arendt et al. (2007) studied 119 marijuana-dependent subjects and discovered that subjects who reported problems controlling their violent behavior more often used marijuana to reduce their aggression, but while intoxicated they more often reacted with aggression. However, even among this group aggression was one of the least likely reactions during marijuana intoxication.

And here is his summary of some of the studies that found a positive association between marijuana use and violent behavior:

  • In a study of 85 patients in the first episode of psychosis, Harris et al. (2010) report that regular cannabis use was associated with serious aggression.
  • Using cross-sectional survey data on adolescents, Walton et al. (2009) discovered that teens reporting peer violence and dating violence were more likely to smoke marijuana.
  • Brady, Tschann, Pasch, Flores, and Ozer (2008) examined longitudinal interview data on Mexican-American and European-American adolescents, and they found that adolescents who had used marijuana at age 15 were more likely to report violence perpetration at age 19.
  • Analyzing cross-sectional data from Dutch adolescents, Monshouwer et al. (2006) report that cannabis use was associated with aggressive behavior.

Note that none of these latter studies was designed in a way that could prove marijuana use caused aggressive or criminal behavior.

Research with prisoners

In his paper, Ostrowsky also reviews the research that specifically involved prison populations. These findings, he says, are less equivocal than the general studies.

“The majority of research on high risk and incarcerated samples has not found a relationship between marijuana use and violent behavior,” Ostrowsky concludes.

Sheriff Stanek may wish to take note.

Confounding variables

As Ostrowsky points out, a major problem with many of the studies that found an association between marijuana and aggression was that they failed to control for confounding variables — most notably, alcohol and hard drug use.

“Future researchers need to rule out spuriousness before they proclaim that marijuana use ‘causes’ violent behavior,” he writes.

Ostrowsky concludes that “[i]t is evident from the inconsistent findings in the literature that the exact nature of the relation [between marijuana use and aggressive/violent behavior] remains unclear.”

Any statement, therefore, that declares an unequivocable “direct connection” between the two is inaccurate.

Comments (17)

  1. Submitted by Steve Titterud on 09/20/2013 - 10:44 am.

    Many violent offenders wear blue jeans, so…

    …blue jeans are ALSO an obvious cause of violence.

    Put the two together, and it is obvious that a stoner wearing blue jeans is an extreme risk of going all crazy on you !!

    And they say these cops are ignorant !!

    • Submitted by Adam Miller on 09/20/2013 - 02:49 pm.

      We have to admit it

      There is also a direct connection between blue jeans and violence.

      Also, oxygen. 100% of violent offenders booked into the Hennepin County Jail breath oxygen. There is a direct connection between breathing oxygen and violence.

      • Submitted by Steve Titterud on 09/20/2013 - 09:10 pm.

        Good catch !! Forgot about that oxygen factor, and it is…

        …so obvious !!

        The scope of Sheriff Stanek’s mind dragnet is not broad enough.

        When they let all the oxygen-breathing, milk-drinking, jeans-wearing people through their sieve – as if they were ordinary citizens – no wonder there’s so much violence !!.

  2. Submitted by Kelly Guncheon on 09/20/2013 - 11:03 am.

    Outlaw milk

    I can safely argue that 100% of the people serving in state and federal prisons drank milk when they were young. Clearly it is a gateway food that should be banned.

  3. Submitted by Lance Groth on 09/20/2013 - 12:23 pm.


    The only thing we can conclude from the sheriff’s statements is that he is not a deep thinker.

  4. Submitted by Robert McManus on 09/20/2013 - 12:32 pm.

    I always listen to what the cops(who of course get no money to continue the disastrously flawed, unconstitutional policies of the drug war) have to say about drug legalization. They are such a force for social progress.

  5. Submitted by Ray Schoch on 09/20/2013 - 01:21 pm.

    The sheriff is confused

    It might be most productive to simply roll the first 4 comments together to illustrate just how badly the sheriff has wandered off the track of reason and into the swamp of “I don’t know what I’m talking about.”

  6. Submitted by Gail O'Hare on 09/20/2013 - 04:02 pm.

    Not funny

    I cringed all the way through the sheriff’s comments. Could we teach basic logic and statistics to everyone, just like reading and arithmetic? It’s genuinely frightening to think people in power are so limited. Clear reasoning requires fundamental understanding of cause and effect.

    Or is Stanek canny enough to know that we’re losing enthusiasm for incarcerating harmless drug users, so he’s fighting to save law enforcement and prison jobs?

  7. Submitted by Bill Kahn on 09/20/2013 - 04:47 pm.

    Stanek Rare Breed of Law Enforcement Officer, Going Extinct

    It is becoming more and more obvious to law enforcement officers the world over that prohibitions are the real cause of the violence.

    We need more leaders in law enforcement who think like the folks in Law Enforcement Against Prohibitions:

  8. Submitted by Steve Titterud on 09/20/2013 - 05:28 pm.

    Want to know the level of spending on the “drug war” ?

    Be sure you are sitting down and then see

    I think some of Sheriff Stanek’s budget would come from the “Domestic Law Enforcement” slice of the pie.

    Don’t miss the footnoted items 1 – 78 where a number of categories of expense are explored. Fascinating.

  9. Submitted by Dan Feidt on 09/21/2013 - 08:02 pm.

    homeopathic medicine and cannabis

    In my inquiries about cannabis over the years, in one classic moment County Attorney James Backstrom ran away from me rather than respond to my question about whether cannabis had been used in Chinese medicine as a palliative for centuries.

    Old Chinese medicine could be thought of as one of the forms of what is called in the West “homeopathic” medicine as it was more philosophically about one-ness than seeing a human body as a more mechanized collection of discrete parts as it is sometimes seen in Western mainstream medicine.

    Finally the West is learning of the endocannibinoid receptor system – the old Chinese rather could deduce the existence of this system through treatments working, while in the west there has been plenty of pseudoscience or failed science over the decades that Stanek is basically leaning on here.

    Anyway glad you are taking on Stanek’s misinformation – but let’s remember to give credit to wisdom that certainly existed outside & prior to modern Western medicine, and reflect on why that kind of medical philosophy was able to deliver good decisions and wisdom for other human beings in need of help.

    It is also important to note that Stanek conflated intoxication of violent criminals with testing positive for cannabis, which is the kind of dark ages anti-science we need to leave behind. Many in law enforcement, when speaking anonymously, will confirm they would rather deal with routine cannabis users than heavy drinkers in terms of violence and social problems.

  10. Submitted by Tom Suther on 09/23/2013 - 09:06 am.


    yes this is all about money and some real dumb law enforcement folks.

    These are the people that the governor and congresscritters listen too. I have no idea they would listen to such ignorance and stupidity.

    Please un-elect Stanek as if he is this dumb wonder what else he is doing in the community.

  11. Submitted by Steve Rose on 09/23/2013 - 09:11 am.

    “classic mistake”

    Yet two days earlier, Susan makes the mistake she terms “classic” in this column:

    • Submitted by Paul Brandon on 09/27/2013 - 09:57 am.

      Well, sort of. To quote:

      ““Although correlation is not synonymous with causation,” write Bangalore and Messerli, “it seems conceivable that abundant gun availability facilitates firearm-related deaths. Conversely, high crime rates may instigate widespread anxiety and fear, thereby motivating people to arm themselves and give rise to increased gun ownership, which, in turn, increases availability. The resulting vicious cycle could, bit-by-bit, lead to the polarized status that is now the case with the US.”

      “Regardless of exact cause and effect, however,” they add, “the current study debunks the widely quoted hypothesis purporting to show that countries with the higher gun ownership are safer than those with low gun ownership.””

      There is a real causal relationship involved since mass killings are much easier with guns. Agreed that it’s not the tight causality you’d like in an experimental study, I don’t see an obvious third variable that would account for both gun availability and deaths.
      Gun ownership is part of a causal sequence that leads to killing.

      • Submitted by Steve Rose on 09/28/2013 - 06:38 pm.


        Actually, mass killing is easiest with bombs. However, far less than 1% of US homicides occur in a mass killing.

        The study cited fails to debunk because it fails to account for the lives saved by the defensive use of firearms, arguably the most potent defensive weapon known to man. All those unnamed guys standing around the President have one.

        With no personal ownership of guns in Japan, they still hit a suicide rate twice that of the U.S. It shows that people motivated to harm themselves or others will find a way.

        Gun ownership does not lead to killing.

  12. Submitted by Earl Carruthers on 10/21/2013 - 03:07 pm.

    Medical Marijuana

    Well, did they not test the alleged criminals for alcohol? Selective studies on marijuana usage trends and after-effects, that’s what a select few people with limited vision and understanding of medical marijuana have been doing for the last 100 years or so. Let’s ban blue jeans, rock music, alcohol and everything else too.

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