Jumping to conclusions with CDC data

Jul 31, 12 Jumping to conclusions with CDC data

I have seen so much misinformation about the Center for Disease Control’s latest Youth Risk Behavior Surveillance System (YRBS) data that it’s time for me to speak up.

First, take a look at the numbers for yourself.

Now for some quick background:

Drug-legalization proponents and journalists who could use some lessons in interpreting scientific data have publicized claims the 2011 YRBS data don’t support. Among them is that adolescent marijuana use rates in Colorado have fallen since the start of the 2009 boom in dispensaries in this state. This is evidence, legalization supporters say, that regulated storefronts help keep marijuana out of kids’ hands.

Not so fast — and not by a long shot. Here is a short list of reasons why the CDC data do not support claims that adolescent marijuana use in Colorado is on the decline, much less that dispensaries have contributed to a fall in teens’ use of the drug:

  • The data are statistically insignificant. If you understand what a “margin of error” is in political polling, then you understand statistical insignificance. As my wife, Christine Tatum, wrote about this CDC data on another post: “Folks who refer to these numbers as a ‘drop,’ or a ‘decrease,’ or a ‘fall,’ or a ‘decline’ demonstrate they know very little about how to analyze and interpret scientific data. Then again, these people may know exactly what they’re doing — and are just hoping the general public will fall for their deceptive ‘analyses.'” Similarly, Kevin Sabet, a world expert in drug policy, examined the numbers and wrote: “Almost all of the indicators for ALL drugs show an insignificant decline, meaning there are other reasons for the ‘no difference’ between 2009 and 2011 than marijuana dispensaries — unless legalization proponents claim dispensaries also make kids not drink, not smoke, not do cocaine, not do prescription drugs and not do other drugs. The bottom line is this: there is NO difference, AND the NO difference can be found in ALL drugs. The data then do not tell us anything.”
  • The data were collected only a year from the start of the rise of marijuana dispensaries in Colorado. In prevention medicine, there are well known lag times between watershed moments and widespread public impact. Because the data in question were collected only a year from the start of the boom of marijuana dispensaries in Colorado, it is too soon to say how dispensaries have affected marijuana use rates (but if drug legalization supporters insist, they should also review a study I co-authored in the July edition of the Journal of the American Academy of Child & Adolescent Psychiatry.). Given the “prediction windows” that are fairly common and standard in prevention medicine, Colorado won’t begin to have a good idea of how dispensaries have affected adolescent use rates until at least 2013 or 2014.
  • The data do not include teens who were not in school. It is important to note that Colorado has reported record drug-related school expulsions in the last four years. These expulsions are overwhelmingly attributed to marijuana use, officials at the Colorado Department of Education say. It is highly possible that teens who have substance problems did not participate in the CDC’s research.
  •  The CDC’s 2011 numbers could be a flatline because 85 Colorado communities voted to ban dispensaries the previous year, 2010. We could be looking at steady numbers precisely because Colorado voters shut down pot shops, making marijuana less accessible and socially acceptable.






  1. This post deserves an update: today, we received a message from Ed Wood of Colorado, who ardently champions sensible drugged-driving laws and law enforcement.

    He, too, makes valid points about the highly questionable methodology of Daniel Rees’ research. You can read much more here: http://drthurstone.com/base-duid-laws-on-responsible-research

    Here’s to hoping more journalists find this information, ask far tougher questions of Mr. Rees’ research and report much more smartly.

  2. Now I must wade in here because THIS is amusing. Sad, but also amusing.

    See all of the Trackbacks/Pingbacks to this blog post listed under these comments? They started happening right as Rocky Mountain PBS broadcast my debate about the proposed Amendment 64 — which would legalize weed for recreational use in Colorado. What. A. Coincidence!

    I hope you’ll watch that debate, which is posted here: http://video.rmpbs.org/video/2276859400

    My video remarks are bound to help you understand why Amendment 64 campaign honchos are suddenly — and quickly — working to create more haze and confusion around these CDC data. From the trackbacks and pingbacks mentioned here, you can click to read the off-track interpretation of the CDC data that marijuana legalization supporters have posted on several websites in a desperate attempt to debunk what you’ve read here from my husband, Dr. Thurstone.

    Allow me to come right out with it: people pushing for weed legalization are turning to an ECONOMIST — in this case, Daniel Rees at the University of Colorado Denver — and not to a medical researcher and/or medical clinician and/or biostatistician and/or medical specialists in adolescent addiction to inform their “findings” for a reason. Make that very, very good reasons.

    I say we all start asking more questions about those reasons. I, for one, would like to begin by calling on Rees, the economist, to declare all potential and real conflicts of interest.

    Rees the economist not only didn’t receive peer-review from his fellow economists before trumpeting his data analyses to the world. He also failed to consult any of the medical researchers on his own campus. They are FAR more qualified to crunch these numbers and explain these data to the public. And I do mean far more qualified. I am certain the skilled professionals there, who regularly work with these CDC data, would have been happy to help Rees the economist.

    Call me crazy, but something tells me he wasn’t looking for their help and input for a reason.

    As I mentioned during the broadcast, Rees the economist has created quite a stir among experts within the university’s School of Medicine. They are not at all pleased with his handiwork. I’ll stop short of telling you how it has been described to me.

    Let’s just say that if I were Rees the economist, I would refrain from commenting further about these CDC data to a marijuana-legalization campaign, drug-legalization groups and news organizations. I would pick up the phone to connect with scientists who actually work with these numbers and within the field of addiction medicine — starting with experts at the University of Colorado Denver. I would also brace myself for people to start asking very tough questions about the nature and quality of my work.

  3. Thanks for attending the Marijuana Prevention Summit, John. You can find all of the slides Dr. T presented here: http://drthurstone.com/the-big-deal/neuroimages.

    Like you, we have found that when people learn more about the reputable, credible science on marijuana and how it especially harms the developing, adolescent brain, they have a different perspective on the wisdom of marijuana legalization.

  4. Thanks for your talk on this topic at the Marijuana Prevention Summit. I was able to use some of what your shared in a conversation with a Metro State student today, was able to change his mind about legalization.


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