William M. Briggs

Statistician to the Stars!

Bill Clinton’s “Pump Head”

I have never, and will never, read Vanity Fair. Given our culture is already saturated, more mindless celebrity tittle tattle written by besotted suck-ups I do not need. So I missed the piece on Bill Clinton that suggested he might have suffered from a malady called “pump head”, brought on by his heart surgery.

Melinda Back, at the Wall Street Journal, wrote an article on this subject today (I have no idea how long that link will be good) which alerted me to the topic.

When surgeons cut a guy open to chop away at his heart, they usually stop it from beating (presumably, this makes it less slippery). They then hook up a machine, a pump, to oxygenate and circulate the patient’s blood. Some people are concerned that the machine, which is certainly necessary, causes harm, usually mental degradation, to those patients who live through the surgery. Lots of mechanisms have been proposed which might cause this harm, but there is no agreement or even direct evidence that any of them actually do cause harm.

“Pump head”, not to put too fine a point on it, is bunk.

The first “diagnosing” of this strange malady came from a series of experiments that gave people before- and after-surgery mental exams. The researchers found that a certain proportion of people scored worse on the after-surgery tests, which confirmed the idea that people get dumber after having been on the pump.

To show this, they created a conglomeration of the tests that were given using a dicey statistical technique called “factor analysis,” a method with which it is far too easy to generate spurious results. But even given that this method was applied properly and conservatively, there is still a large, glaring error in these analyses.

It is true that some people scored worse on the conglomeration-test after surgery. This is the sole evidence for “pump head.” But it is also true that some people scored better! In fact, the same exact proportion of people who scored worse, scored better. This means you could just as easily write a paper suggesting open-heart surgery as a method to boost IQ!

The problem was that the original researchers never bothered to look for people who scored better, only those who scored worse; they only examined those patients who looked like what they hoped they would look like, that is, those who seemed to get dumber.

What’s really going on is nothing more than the banal phenomena of “regression to the mean.” If you take a test, some days you will do better, other days worse. Everybody has a natural background variability. Now, if you do score high one day, chances are that the next time you take the test, you will achieve only your average performance. Same thing if you first tested low: next time, you’re likely to improve.

If you look at a bunch of people who take the test, and create two groups, one with those who scored high and another with those who scored low, and then later re-test both groups the high group will show lower scores on the re-test, and the low group will show higher scores. It is impossible for the situation to be other than this.

This phenomena is a boon to researchers who want to prove spurious effects, because, as I said, it is impossible for it not to manifest itself. You can prove the efficacy of or show the potential harm of absolutely any therapy this way.

So pump head, so far as it has been demonstrated in tests like these, is nonsense.

This means that Bill Clinton is probably no dumber now than he was before.


  1. “It is impossible for the situation not to be other than this.” 🙂

    I assume you meant “It is impossible for the situation to be other than this.” or “It is impossible for the situation not to be like this.” or perhaps “It is impossible for the situation not to be non-different from this.”?

  2. Briggs

    June 10, 2008 at 9:28 am

    Damn English language. Thanks, Gorgasal.

  3. All things considered, “pump head” seems like a useful term to apply in certain situations, whether it has any validity or not. It has a ring to it. I am sure I will find opportunities to zing it out there, but that’s just my acerbic nature. So thank you, intended or not.

    It’s a great language, isn’t it?

  4. Nice to see you back blogging, although the stats text was also somewhat interesting.

    This is, unfortunately, what passes for science these days. I think there’s a book in popularizing the extent to which science has now become bunk. Want to co-author?

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