Vaccines are still good for you

People seem to have been talking about some new reports that claim (yet again) a connection between vaccines and autism. The latest versions go further, alleging a cover-up by the CDC. The most important thing to know about this is that the overwhelming scientific consensus remains that vaccines are not linked to autism. They do, on the other hand, prevent vast amounts of suffering due to preventable diseases. The anti-vaccine folks do enormous harm.

(Although I have a few other things to say, the main point of this piece is to link to an excellent post by Allen Downey. The link is below, but it’s mixed in with a bunch of other stuff, so  I thought I’d highlight it up here.)

The usual pro-science people (e.g., Phil Plait) have jumped on this most recent story, stating correctly that the new report is bogus. They tend to link to two articles explaining why, but I’d rather steer you toward a piece by my old friend Allen Downey. Unlike the other articles, Allen explains one specific way in which the new study is wrong.

The error Allen describes is a common one. People often claim that a result is “statistically significant” if it has a “p-value” below 5%. This means that there is only a 5% chance of a false positive — that is, if there is no real effect, you’d be fooled into thinking there was an effect 5% of the time. Now suppose that you do 20 tests. The odds are very high in that case that at least one of them will be “significant” at the 5% level. People often draw attention to these positive results while sweeping under the rug the other tests that didn’t show anything. As far as I can tell, Allen’s got the goods on these guys, demonstrating convincingly that that’s what they did.

The other pieces I’ve read debunking the recent study have tended to focus on the people involved, pointing out (correctly, as far as I know) that they’ve made bogus arguments in the past, that they have no training in statistics or epidemiology, etc. Some people say that you shouldn’t pay any attention to considerations like that: all that matters is the content of the argument, and ad hominem considerations are irrelevant. That’s actually not true. Life is short. If you hear an argument from someone who’s always been wrong before, you might quite rationally decide that it’s not worth your time to figure out why it’s wrong. Combine that with a strong prior belief (tons of other evidence have shown no vaccine-autism link), and perfectly sound Bayesian reasoning (or as I like to call it, “reasoning”) tells you to discount the new claims. So before I saw Allen’s piece, I was pretty convinced that the new results were wrong.

But despite all that, it’s clearly much better if someone is willing to do the public service of figuring out why it’s wrong and explaining it clearly. This is pretty much the reason that I bothered to figure out in detail that evolution doesn’t violate the laws of thermodynamics: there was no doubt about the conclusion, but because the bogus argument continues to get raised, it’s good to be able to point people towards an explanation of  exactly why it’s wrong.

So thanks, Allen!



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Ted Bunn

I am chair of the physics department at the University of Richmond. In addition to teaching a variety of undergraduate physics courses, I work on a variety of research projects in cosmology, the study of the origin, structure, and evolution of the Universe. University of Richmond undergraduates are involved in all aspects of this research. If you want to know more about my research, ask me!

2 thoughts on “Vaccines are still good for you”

  1. Many people lack a capacity for logical reasoning. One of the best examples of this (though not as dangerous) is to be found among high-end hi-fidelity aficionados. Not uncommon is the belief that colouring the edge of a CD with a felt-tip pen (green produces the best results) will substantially improve the sound of a CD. Like with homoeopathy, there are two arguments against this: lack of a plausible mechanism, and the observation that it just doesn’t work. In the case of the CD-colouring, this can be easily shown to derive from an April Fool spoof article. However, some people still believe it, even if they know the source of the legend. There are similar legends about freezing CDs to improve the sound etc. There are many such delusions, such as fat cables. Yes, really thin cables are bad, but they have to be really thin. Since the analog signal has travelled through wires the width of a human hair before going to the speaker output, $100-per-inch cables to the speakers can’t help.

    In the case of the hi-fi folks, one can understand this a bit: in the old days, sometimes simple things (a better needle, better speaker placement) really could boost the sound quality dramatically, so they might think that similar easy tricks would do the same. Also, in the analog days, there was a bigger difference in quality between good and bad equipment.

    The vaccines-cause-autism claim can be traced to Andrew Wakefield, who started this rumour, probably because he had stake in different vaccines which supposedly did not cause autism. Both the scientific and legal establishments have established his guilt beyond doubt. (And it is a big guilt; he is responsible for thousands of unnecessary deaths.) He probably chose autism for several reasons: no-one understands the causes of it (so people might be inclined to believe in his idea), it is not curable (puts fear in people), autism is usually diagnosed shortly after many vaccines have been given (correlation does not imply causation, but many think it does).

    Historically, it was good to believe in bogus causes; the danger of not doing so and occasionally missing a real cause is much greater than any benefits gained from learning which are real and which are not. (In many cases, one would not survive long enough to find out.)

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