damnum absque injuria

November 22, 2009

We’re Scientists And You’re Not

Filed under:   by Xrlq @ 1:03 pm

Last week, the U.S. Preventative Services Task Force brought Sarah Palin’s death panels into the fore by recommending women in their 40s stop having regular mammograms. No, they didn’t make this tin-eared recommendation for purposes of saving money (primarily), but regardless of their motive the timing could scarcely have been worse (or, depending on your perspective, better). Today on that show that used to be good when Tim Russert was around, that bimbo Nancy Snyderman would not shut up about how this panel’s recommendations were “science” and everyone else’s objections were “politics.” The “science?” That would be a finding that:

For every 1,000 women screened beginning at age 40, the modeling suggested that just about 0.7 deaths from breast cancer would be prevented, while about 470 additional women would receive a false-positive result and about 33 more would undergo unnecessary biopsies.

Most of us silly, unedumacated non-scientists have a hard time picturing anyone other than Keith Richards undergoing 0.7 deaths, so let’s adjust the figures to account for the odds of one whole person dying instead:

For every 1,429 women screened beginning at age 40, the modeling suggested that only one death from breast cancer would be prevented, while about 671 additional women would receive a false-positive result and about 47 more would undergo unnecessary biopsies.

Depending on whether you trust the modeling (and there’s no way to tell whether you should) those numbers arguably science but the panel’s conclusions are not. A scientists is no more (or less) qualified than anyone else to decide whether it’s better to undergo a simple procedure that is 1,429 times more likely to waste your time than kill you. Unless of course you’re one those scientifically illiterate crazies who actually take some comfort in knowing you don’t have breast cancer, in which case it has a 53% chance of telling you that right off the bat, a 44% chance of briefly spooking you only to put your mind at ease after further tests, and a 3.3% of leading to an unnecessary biopsy and a 0.7% chance of saving your life? Rather than make broad pronouncements as to who should or should not get screened, why not just tell women what the odds are and let them choose* for themselves? By going the next step and telling us what we should do with these numbers, the panel (along with its apparatchiks like Snyderman) shows itself to suffer from the same know-it-all syndrome that plagues all those non-climatologists who eagerly sign as “scientists” the various and sundry petitions for and against global warming or the medical doctors who eagerly dispense “medical” opinions on everything from guns to crime, and even monster trucks.

Also suspect is the panel’s conclusion that waiting until age 50 would cut in half the number of false positives. Without further explanation, I’m inclined to call bullshit not only on the conclusion but also on the alleged science itself. What on earth trait does the average healthy 40 year old woman have that she won’t have 10 years from now, that will somehow trigger a false positive on a mammogram now but not then? And if we know what that is (assuming “it” even exists), why can’t we test separately for that and eliminate the problem of false positives altogether? If, as I suspect, the answer is “because the modeling says so,” then that tells you everything you need to know about the model – and damned near nothing else. But don’t listen to me, I’m not, like, a scientist.

UPDATE: Jody calls bullshit on that last bit of bullshit-calling. Apparently, women in their 40s really do have harder tissue that can more easily register a false positive. This doesn’t affect my main point, of course.

*Yes, I know, it technically doesn’t count as a “choice” because we’re talking about a patient’s choice to obtain a medical procedure rather than an abortion. Nevertheless, I think there is something to be said for extending this quaint concept of “choice” to other venues.

3 Responses to “We’re Scientists And You’re Not”

  1. Jody Says:

    What on earth trait does the average healthy 40 year old woman have that she won’t have 10 years from now, that will somehow trigger a false positive on a mammogram now but not then?

    Breast tissue becomes less dense as you (if you were a woman) age, which makes scanning easier (improves imaging SNR, if you will).

    See here:

    Mammography is a less sensitive test for women aged 40 to 49 years than for older women. The authors of one study examined 576 women who developed invasive breast cancer following a screening mammogram to determine whether greater breast density or faster growing tumors among younger women explained the lower sensitivity. They found that more younger women with cancer had developed interval cancers. They also found that greater breast density explained most (68%) of the decreased mammographic sensitivity in younger women at 12 months, whereas at 24 months, rapid tumor growth and breast density explained approximately equal proportions of the interval cancers

    Otherwise, I agree with the rant.

  2. Marty Says:

    It also becomes less dense the more times you mash it between those mammography devices.

    Might as well just cut em off and eliminate the risk completely :P

  3. Aunt Ruth Says:

    Screening has risks. It’s been reported before:

    http://www.webmd.com/breast-cancer/news/20031014/does-mammogram-risk-outweigh-benefit

Leave a Reply

Subscribe without commenting

 

Powered by WordPress. Stock photography by Matthew J. Stinson. Design by OFJ.