<p><strong>Short answer</strong><br>
The control subjects were abstinent for <strong><em>at least</strong> 60 and 90 days</em>, respectively.</p>

<p><strong>Background</strong><br>
The article you cite mentions the following in the Materials and Methods, and I quote:</p>

<blockquote>
  <p>From the remaining subjects, age, gender, and AUDIT scores were used to create a matched control group reporting no marijuana use in the past 60 d.</p>
</blockquote>

<p>A similar procedure was used for the 90-day control group. I agree with you that this method, i.e., <em>at least</em> 60-90 days of abstinence, leaves plenty of room open for variance. Probably a large part of the identified controls have not smoked marijuana <em>ever</em>, others maybe once or twice, but who knows? I think you have identified a very good point of critique.</p>

<p>The article mentions two citations (p.1506, Materials and Methods, first paragraph: Filbey 2008, Claus 2011) with respect to this protocol, and I followed these as I was curious if they actually controlled for this shaky part of their method to generate a control group. The first reference is actually not in the reference list(!) and after a thorough search I dug it up. I couldn't find any details on the questionnaire, however, and the same holds for the other article. If it is important to you you may want to read these articles in full (I just scanned the section on the questionnaire) to search for clues.  And contacting the authors is never a bad thing either. For now, I conclude you are right and the methods are shaky.</p>

<p>However, <strong>flawed</strong> as mentioned in your question title is a big word. As long as you take the methods used into account, you can place the results in perspective against other studies that, perhaps, used study participants that have never touched any THC-containing product in their lives.    </p>

CC BY-SA 3.0
2015-02-16T14:37:18.897Z
Thanks for your explanation! I already contacted one of the authors concerning the issue about the 60days abstinent control group (Rachel Thayer). So far I did not receive an answer. I agree flawed is a strong word, but you might agree that the title of the study also makes strong claims. In the words of Carl Sagan : "Extraordinary claims require extraordinary evidence" The study fails to provide such evidence due the methodological weakness..
CuriousIndeed
CC BY-SA 3.0
2015-02-16T10:34:17.190Z
2015-02-16T10:59:12.500Z
2015-02-16T10:59:12.500Z
AliceD
<p>I'm relating to this study: <a href="http://www.jneurosci.org/content/35/4/1505.short" rel="nofollow">http://www.jneurosci.org/content/35/4/1505.short</a></p>

<p>The researchers found no differences in subcortical brain structures for daily Cannabis users vs. controls. However the controls were only abstinent for 60 (adults) or 90 (adolescents) days. IF Cannabis use was associated with changes in brain structures which take more than 60-90 days to normalize, these (presumably) insufficient abstinence periods could be the reason why no differences between user and controls could be found. Why did they not use a control group which had not used Cannabis at all?</p>

<neuroscience><methodology>
Colorado Boulder study about brain morphometric measures of Cannabis users methodologically weak?
CuriousIndeed
# Colorado Boulder study about brain morphometric measures of Cannabis users methodologically weak?

(Asked by: username_0 on 2015-02-16)

I'm relating to this study: <http://www.jneurosci.org/content/35/4/1505.short>

The researchers found no differences in subcortical brain structures for daily Cannabis users vs. controls. However the controls were only abstinent for 60 (adults) or 90 (adolescents) days. IF Cannabis use was associated with changes in brain structures which take more than 60-90 days to normalize, these (presumably) insufficient abstinence periods could be the reason why no differences between user and controls could be found. Why did they not use a control group which had not used Cannabis at all?

**Tags:** neuroscience, methodology


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## 1 answers

### Answer by username_1 on 2015-02-16. Score: 3

**Short answer**  
The control subjects were abstinent for ***at least*** 60 and 90 days, respectively.

**Background**  
The article you cite mentions the following in the Materials and Methods, and I quote:

> From the remaining subjects, age, gender, and AUDIT scores were used to create a matched control group reporting no marijuana use in the past 60 d.

A similar procedure was used for the 90-day control group. I agree with you that this method, i.e., *at least* 60-90 days of abstinence, leaves plenty of room open for variance. Probably a large part of the identified controls have not smoked marijuana *ever*, others maybe once or twice, but who knows? I think you have identified a very good point of critique.

The article mentions two citations (p.1506, Materials and Methods, first paragraph: Filbey 2008, Claus 2011) with respect to this protocol, and I followed these as I was curious if they actually controlled for this shaky part of their method to generate a control group. The first reference is actually not in the reference list(!) and after a thorough search I dug it up. I couldn't find any details on the questionnaire, however, and the same holds for the other article. If it is important to you you may want to read these articles in full (I just scanned the section on the questionnaire) to search for clues. And contacting the authors is never a bad thing either. For now, I conclude you are right and the methods are shaky.

However, **flawed** as mentioned in your question title is a big word. As long as you take the methods used into account, you can place the results in perspective against other studies that, perhaps, used study participants that have never touched any THC-containing product in their lives.

> **Comments:**
> **username_0**: Thanks for your explanation! I already contacted one of the authors concerning the issue about the 60days abstinent control group (Rachel Thayer). So far I did not receive an answer. I agree flawed is a strong word, but you might agree that the title of the study also makes strong claims. In the words of Carl Sagan : "Extraordinary claims require extraordinary evidence" The study fails to provide such evidence due the methodological weakness..  

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