It was claimed in this press release that exposure to second hand smoke (aka environmental tobacco smoke, ETS) raises blood pressure in boys. It would be difficult to make up a better example of why epidemiology is widely considered to be junk science. It did not generate many news reports (just a handful of newspapers, British and Asian for some reason, and the usual websites that just reprint all health press releases), but it the type of claim might have made the news, and might still, so it worth dissecting based on the press release. The press release was touted by the American Academy of Pediatrics (yes, that would be the same people who publish the junk science journal, Pediatrics) who appear to be the sponsor of the conference where the results were presented. Based on that, we might charitably think that the study authors were just honestly reporting simple study results and the publicity seekers tried to turn it into something else. However, one of the authors actively contributed the the absurd claims in the press release, so the researchers are equally to blame.
[Note: I had already written most of this earlier today when I noticed that Chris Snowdon posted about it, including a request for my input. I added a few more points in response to the requests for clarification he emailed me. Since my goal in this series is to address points of confusion, I always welcome questions from any reader about what people think needs explaining.]
The press release began with several paragraphs about how terrible high blood pressure is in adults and then claimed, "that boys ages 8 to 17 years old who were exposed to secondhand smoke had significantly higher systolic blood pressure than boys not exposed to tobacco smoke." But a glance at the abstract of the study reveals that the increase was only a bit over 1 mmHg (i.e., about one point on the familiar scale with numbers like "your blood pressure is 116-over-82"). This is hardly "significant"; a better word would be "trivial".
The press release tries to spin this as important at the population level despite being small for any individual. The is rather disingenuous when juxtaposed against calling the result significant. More important, even if the claimed effect followed from their data (it doesn't – keep reading) there is no evidence of a population effect. The author is mistaking a small increase in risk for a disease with a small increase in a characteristic. That is, if some ubiquitous environmental toxin increased everyone's risk of liver cancer by 1%, it would not be a huge worry for any one of us, but it would be causing thousands of extra cancers in the population. But this tiny change in blood pressure may or may not represent any extra risk of anything, so multiplying the extra risk of epsilon or perhaps zero by lots of people still does not necessarily add up to much. Moreover, it seems almost certain that even if this study had actually shown the claimed effect of ETS exposure in childhood, any residual effect in adulthood would be substantially less. That is, by the time higher blood pressure created a risk for bad outcomes, the trivial effect of ETS exposure during one's long-past childhood would have faded away.
But, as I said, there is not really evidence of a bad effect. The numbers actually show a good effect, though what they really say is "this study showed nothing of importance".
The obvious fatal flaw in the attempt to make a big deal of the study that the result for girls was exactly the opposite the touted result for boys. Actually it was bigger. The girls had a reduction in blood pressure of well over 2 mmHg, so if this study is to be believed, any bad effect for males is more than offset by a good effect for females. If we are supposed to believe that one result from the study is right, then we are obliged to believe the corresponding results for other subpopulations. Moreover, the result for the population as a whole is always more important than the subpopulation results. Funny that they did not bother to mention that, since it would be a "significant" (by their standards) protective effect of about 1 mmHg (.5*(+1) + .5*(-2) = -1). So the real first headline from the study is:
Second hand smoke exposure reduces blood pressure in childrenIt is not just about boys having an effect in one direction and girls in the other. I noticed that several commentators already made that observation today, but they overlooked the even more important point that the (unreported) overall results show that ETS is beneficial on average. A better interpretation would, of course, be to consider all three results (all, male, female) to be a bit of technical information that might contribute to some honest analysis someday, but that have no meaningful implications in themselves. It follows from this that touting one result in a press release or writing the conclusion that this "provides further incentive to expand policies that create smoke-free environments for children and adolescents" is a crime against honest science.
In the press release, the study author, Jill Baumgartner from University of Minnesota (surprise! - though the study apparently was done at Wisconsin), seeks an excuse for why we should believe the result she likes politically, and ignore the one she does not like by claiming, "These findings support several previous studies suggesting that something about female gender may provide protection from harmful vascular changes due to secondhand smoke exposure." Um, yeah, except the girls were not "protected" from an effect, they actually had a rather larger effect – just in the "wrong" direction. So, again, if the results were to be believed, the conclusion should be that we have "further incentive to create smoke-free environments for boys, but should encourage girls to suck down some smoke." Of course, an honest analysis would be that this study provides no support for either of those recommendations.
Also, I did not have the impression that sex has been shown to be a major effect modifier for ETS. The three choices there are (a) she is cherry-picking one or two studies that tend to support her claim as if they were all the evidence (she certainly has demonstrated skill at cherry picking), (b) she know more than I do (you can be the judge), or (c) she is just making it up (I would not rule it out).
Further review of the abstract (all that is available other than the press release) shows that there is no dose-response trend. The one-fifth of the population who have approximately zero serum cotinine (a measure of nicotine exposure and thus degree of ETS exposure) have lower blood pressure compared to the other four fifths, but among the latter there is no trend as the cotinine increases. Among other things, this means that the subjects who actually smoke (who would comprise about half of the one-fifth of the population with the highest cotinine) were the same as those exposed to a bit of ETS. I suppose this is in keeping with the current propaganda that ETS is so bad for you that if you are exposed to any of it then you might as well smoke, but no one honestly believes that is true. But propaganda aside, it does create some serious doubt about the results. Equally damning is that the difference between the lowest and second-lowest fifth is the same as the lowest compared to those with higher exposure. But even by the standards of ETS exposure, the difference in exposure between the lowest two groups is trivial; they would both be characterized by no one smoking in their home or any place else they spend a lot of time. This is actually as much of a fatal problem with over-interpreting the results as the boy-girl contrast is, it just requires a bit deeper an analysis to recognize it.
My epistemic point is not that the result should not have been presented. Even though it is full of oddities and the numbers are trivial, the data is what it is and might usefully inform something someday. Real scientists do not suggest that research results be censored. But touting a blatant exaggeration and misinterpretation of the results to the press is lying, pure and simple.
As a final note, some readers might think that this is just something that anti-tobacco or the American Academy of Pediatrics might tout, but real epidemiologists would not be so dishonest or fall for this. But it reminds me of an example that was my favorite teaching and methodologic example for years, about a decade ago (I won an award for my article about it). The decongestant medicine phenylpropanolamine (PPA) was banned in the US and then most of the world based on a single sketchy study. The touted headline from that study was that PPA caused an increase in stroke risk in young women. What everyone failed to notice or care about was that it had a protective effect for men – less than half of magnitude of the bad effect for women, unlike the greater effect in the present example, but still protective. Funny how everyone, in their inexplicable frenzy to ban this drug, decided that only part of the evidence from the same study counted rather than simply warning women against taking it. Junk science indeed.