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.....and cigarette lighters cause lung cancer

11/21/2014

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This press release reports on this new article, which asserts that kids born to moms who took antibiotics during pregnancy were 84% more likely to turn out obese at age seven.  The authors note that previous studies have reported that antibiotics early in life may be associated with later obesity, but that this is the first published claim that maternal antibiotic use in the second or third trimester of pregnancy increases risk of offspring obesity. 

The analysis is based on 436 mother-child pairs in which 70 (16%) had antibiotic exposure in the defined gestational age window. 
Ignore for a moment the obvious concerns about large effect estimates from small samples, and just ask the question:  how was it that moms came to be exposed?  Few people gobble down antibiotics for fun or because they taste so good, so you'd have to think that maybe these mom's were SICK.   Therefore, rather than blaming the antibiotics, might not we blame the reason for taking the antibiotics?   Or, maybe it is a marker for being the kind of woman who gets sick a lot.   Obesity is a risk factor for many illnesses, so maybe it is just that obese women give birth to kids who are more likely to end up obese, and that any marker for this (e.g. big pants) can look like a cause of kids later becoming obese, but is not a cause, just a marker. 

I am starting to sympathize more and more with economists and think that we should not even entertain an epid study unless they have an identification strategy based on some exogenous source of variability.  These authors do mention in the obligatory section on study weaknesses that maybe it is the reason for the antibiotic prescription, and not the antibiotics themselves, that are associated with the outcome.  But then they brush this aside and the eminently more plausible hypothesis (confounding by indication) is never mentioned in the more sensationalist press release.  We are losing all credibility because of studies like this.....


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This Press Release is a Lie

11/10/2014

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This news story about this newly published article begins with the claim:

"A new study of emergency department patients in 18 countries, made available online by the scientific journal Addiction, shows that the risk of injury caused by acute alcohol consumption is higher for women compared with men." 

This claim is surely false, although the authors do not provide the information in the paper necessary to evaluate the claim one way or the other.  The sex comparison is in Table 3, but no absolute risk information is provided anywhere.  And not only the journalists are at fault here, because the authors also make the same false claim in the discussion section:

"
Injury risk was similar for males and females up to three drinks prior to injury, but then appeared to increase more rapidly for females and estimates diverged at higher volume levels." 

This sort of misleading risk relativism is a curse that we must be vigilant against! 

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Why does it always have to be genetic?

10/15/2014

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This new paper (and this press report) looks at Louisiana parishes in which (according to 2000 census) 5% or more of households spoke French at home.  They do this to identify Acadians as an ethnically unique group with racial predisposition to colon cancer.  Indeed, they note that these parishes have among the highest colon cancer rates in the US.  
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I found it kind of weird that they focus almost all of the discussion on genetics, when this region is also well known as an environmental disaster area, for example due to its density of petrochemical and oil facilities, the backbone of the local economy (in conjunction with famously lax environmental regulation and horrendous occupational protections).  To be fair, there are a few paragraphs in the discussion section about potential environmental and dietary exposures as alternate explanations, but really if you look at the article, abstract and boxed highlight points, it is all about genetics. 

This predisposition hypothesis seems especially weak to me, however, in light of this plot in the paper:

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The “Acadian 9” are the 9 parishes with the highest proportions of French speakers.  The “Acadian 18” are all of the southern Louisiana parishes highlighted in the map above.   As you can see, the excess rate that is the focus of this article is only for men.  Women have almost exactly the same rate in every comparison (i.e. with the state as a whole and with US as a whole). This seems to me therefore especially suspicious as a putative genetic effect, and looks much more like something occupational.  I don’t see that the authors comment on this sex difference anywhere in relation to their hypothesis of ethnic predisposition.  

Finally, what is with this census data?  Almost no native-born Louisianans speak French at home anymore.  French-language education was banned just about 100 years ago.  I have spent a lot of time in this region of Louisiana and have only met one person who could speak Cajun French in complete sentences, and he was in his 80s.

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