28 June 2011

Unhealthful News 179 - Getting molested by TSA is starting to look pretty good

Oh it is going to be fun to watch this one play out.

A few blogs have started putting out various versions of the story that the new x-ray body scanner airport security machines that are increasingly installed in major US airports (which the bloggers call "naked body scanners", so they are making clear their opinion about them) are causing an elevated risk of cancer for the Transportation Security Administration officials who are operating them, and that the claims that they were safe were actually based on approximately nothing.  The latter seems quite plausible.  I am a bit doubtful about the former, but it is an interesting story.

In any case, it is a fun day for the Freedom of Information Act, which revealed some of this information, as well as the source of my previous post from earlier today.

There are definitely grounds for suspicion about the whole program.  Some European airports have installed full body scanners that do not use ionizing radiation, and thus are undoubtedly safer, but there are rumors that the US is using an inferior product because the manufacturer is well connected.  I am not sure about that, and it did not show up in anything I saw today, but I am sure it will come back into the narrative, so I will leave it to those who are better at that kind of investigation.  Some of the points that came out this week were rather more interesting:  Far from saying the machines are perfectly safe, as the US authorities claimed they had said, various researchers made clear to the government that they could offer no such assurances and they even suggested that TSA workers should avoid standing near the machines which, of course, is safer than being the passenger standing inside them. 

The claims that the radiation dose is acceptable seemed to be based on the assumption that it was evenly divided throughout the body rather than being concentrated in the skin, creating a much higher local dosage that could cause skin cancer.  However, a lower dosage spread more evenly might create just as much cancer, just at low levels in each organ, and most skin cancers are not that threatening, so this might be a good thing.  It is quite a muddle.  But what is clear is that the information given the public was inaccurate.  It is also interesting that TSA agents asked for dosimeters (which measure cumulative radiation exposure and are common for lab workers, reactor workers, etc.) but were refused.

All of this information makes the government's behavior look very sketchy, and the charges against them are quite plausible.  Meanwhile, no plausible response to the charges is apparent.  From an epistemic perspective, the existing accusations and criticisms clearly put the burden of proof on those who are claiming safety, and they seem to have nothing.

On the other hand, the claim that will probably generate the most interest is pretty much groundless without further information.  TSA screeners in Boston have complained about elevated cancer rates, and the allegation is that TSA authorities have dismissed the claim and tried to cover it up.  This is a classic case of a cancer cluster, as I have written about in this serious previously.  It is always the case, due to the random distribution of disease occurrence, that some group of people somewhere has a very high rate of some cancer or other disease.  The fact that they self-identify does not tell us much because it is almost impossible to tell a chance cluster from one that is being caused by some exposure.  Indeed, we cannot even be sure that there is an elevated rate in this case, since there seem to be no numbers forthcoming.  Moreover, the claim is that there is also an elevated rate of stroke and heart disease, which are not plausibly related to the low-level radiation.  Finally, the machines have not been in place long, and almost all cancers take much longer than that to manifest; the basal cell carcinoma that has been proposed as the greatest risk typically appears more than a decade after the triggering exposure (usually a bad sunburn). 

So the Boston cluster probably signifies nothing, and the "cover up" – i.e., realizing that there is not a plausible causal relationship and not pursuing the matter – was a reasonable response. But in light of the real cover-ups that have occurred, and the general failure to understand the cancer cluster statistics problem, it could prove mighty embarrassing.

Oh, and for the record, a few days ago, before this story broke, I was directed to go through one of those scanners and refused, insisting on a manual search.  This was not because I was intrigued by the thought of being felt up, but because I never believed the claims about the safety of those machines.  Even though I am sure the risk is very small (and so I would not have done this if the cost to me were high, like I did not have a half hour to kill before my flight boarded anyway), it seems to me to be an obligatory act of civil disobedience, to demand the slow labor-intensive option as a protest against the dishonest way in which we have all been exposed to this bit of potentially dangerous security theater.

[Unrelated:  Those of you who are working on learning the nuances of epidemiology by reading this series might want to check out my ongoing comments at this post, which currently focus on distinguishing confounding from causal intermediaries, but are expanding into other points.]

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