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When they warn of rare disorders, these prenatal tests are usually wrong

nytimes.com

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Re: When they warn of rare disorders, these prenatal tests are usually wrong

#31

Post by don-code »

I am not a parent, but the criticism of the article appears to be around a misunderstanding of statistics, or at least how to apply them. While I agree that criticism is completely correct, it overlooks the human nature of the people receiving the tests. At an already-stressful point in someone's life, it seems almost like bad bedside manner for the medical community, even if in an automated fashion, to tell people that there might be a complication looming.

This _does_, however, seem like a framing issue, more than a utility issue. If the tests are 100% accurate at detecting true positives, they're a great aid. But rather than framing the tests as a be-all, end-all source for information, why not frame them as "a test that suggests whether or not you should get other tests"? That simple wording change would save a great deal of added stress on someone starting or growing a family.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#32

Post by giantg2 »

treis wrote: post #13
inglor_cz wrote: post #8

Earlier quoted context omitted.

This would be valuable for running some extra tests (possibly more expensive, but more accurate), but not for, say, decision to abort the kid, which is what usually "hangs in the air" after such a test result.

That depends on the person though doesn't it? I'm not sure what I'd do in that situation. But 7% seems awfully bad odds for painful and debilitating life.

I guess that depends on the exact scenario. There are likely people with a variety of conditions who enjoy their lives vs having not been born. It brings up a seemly logical contradiction that we terminate fetuses (potentially viable in some cases) on the assumption that they don't want that life yet we don't allow people who want to kill themselves to do so.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#33

Post by SpicyLemonZest »

halpert wrote: post #30
SpicyLemonZest wrote: post #25

Earlier quoted context omitted.

Their infographics convince me that they understand the statistics. But one of the key issues here is that the statistics are radically counterintuitive in a way that most people don't understand - the patients, the testing companies, and even some medical staff all incorrectly believe that a positive test for a rare condition means you probably have the condition.

Their graphics say the tests are “84% wrong.” Do you really feel that’s an accurate description? That doesn’t feel like an accurate description to me, and their usage of “wrong” in this context highlights that they don’t understand the distinction and importance of true positives, false positives, true negatives, and false negatives when measuring accuracy.

I really feel it's an accurate description. If you get a positive result on the test, there's a 16% chance your fetus has a 1p36 deletion and an 84% chance they don't.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#34

Post by halpert »

SpicyLemonZest wrote: post #33
halpert wrote: post #30

Earlier quoted context omitted.

Their graphics say the tests are “84% wrong.” Do you really feel that’s an accurate description? That doesn’t feel like an accurate description to me, and their usage of “wrong” in this context highlights that they don’t understand the distinction and importance of true positives, false positives, true negatives, and false negatives when measuring accuracy.

I really feel it's an accurate description. If you get a positive result on the test, there's a 16% chance your fetus has a 1p36 deletion and an 84% chance they don't.

As you said “if you get a positive result”. It’s true, if you ignore the 99.9% of the time the test is correct (true negative result), then you can say the test is 84% wrong.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#35

Post by sjckciodjcr »

inglor_cz wrote: post #24
sjckciodjcr wrote: post #17

Earlier quoted context omitted.

NIPT is not supposed to be used for termination decisions. A positive is meant to be “your baby might have this, test further with amniocentesis”.

The article in NYT nevertheless states: "A 2014 study found that 6 percent of patients who screened positive obtained an abortion without getting another test to confirm the result." Maybe people aren't informed enough. It is my experience that some doctors tend to cut conversations short and some people are shy/insecure enough not to pry answers out of them. In this case, that would be a tragedy, given that statisti…

That’s a tragedy. Maybe there needs to be regulation requiring results are delivered by genetic counselors rather than physicians. Or maybe this is willful patient error.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#36

Post by ellisv »

halpert wrote: post #20

How did this article, written by someone who clearly lacks an understanding of basic statistics, make it into the Upshot? They try to make it seem like the test is wrong 85% of the time, but that's not necessarily the case. All we know from the article is that 85 / 100 positive results are false positives, which means the test could actually be quite accurate. If the test correctly identifies 100% of real cases, then…

I disagree. It is clear from the title, “When They Warn of Rare Disorders, These Prenatal Tests Are Usually Wrong”, and the lead that they’re focusing on false positives.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#37

Post by SpicyLemonZest »

halpert wrote: post #34
SpicyLemonZest wrote: post #33

Earlier quoted context omitted.

I really feel it's an accurate description. If you get a positive result on the test, there's a 16% chance your fetus has a 1p36 deletion and an 84% chance they don't.

As you said “if you get a positive result”. It’s true, if you ignore the 99.9% of the time the test is correct (true negative result), then you can say the test is 84% wrong.

84% of people who got a positive test result will end up telling their family "it's OK, the first test was wrong, my baby doesn't have a 1p36 deletion after all". The 99.9% of other people who got true negatives are important from a test design perspective, because specificity is closer to the actual levers you can pull on, but it's not super relevant to the decisionmaking process of someone who gets a positive result.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#38

Post by [deleted] »

SpicyLemonZest wrote: post #19
sjckciodjcr wrote: post #12

This article seems a bit deceptive. We are going through NIPT soon and our doctor went over false positive and false negative rates for the common screens. Our doctor has pointed out some of the screens (esp for rare conditions) are not that accurate. The only procedure with high accuracy, amniocentesis, has a slight risk of miscarriage (our provider quoted 0.3% ) so its still statistically better to take NIPT and th…

"These extra screens shouldn't be offered" seems like exactly the point the article is trying to make.

[deleted]

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#39

Post by bjt2n3904 »

siganakis wrote: post #26

My wife and I went through this a couple of years ago, with a 10 week NIPT calling a rare trisomy (chr 9), which is always fatal within a few weeks of birth. It was absolute hell. The key problem here is the waiting and uncertainty. You have the NIPT at 10w, but you can’t have the amniocentesis until several weeks later. When that came back fine, there were questions about whether it was a “mosaic” meaning only a sma…

So glad to hear that things turned out well for you and your family.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#40

Post by halpert »

ellisv wrote: post #36
halpert wrote: post #20

How did this article, written by someone who clearly lacks an understanding of basic statistics, make it into the Upshot? They try to make it seem like the test is wrong 85% of the time, but that's not necessarily the case. All we know from the article is that 85 / 100 positive results are false positives, which means the test could actually be quite accurate. If the test correctly identifies 100% of real cases, then…

I disagree. It is clear from the title, “When They Warn of Rare Disorders, These Prenatal Tests Are Usually Wrong”, and the lead that they’re focusing on false positives.

It's true they are focusing on false positives, but the authors are using the ratio of false positives to true positives to paint a picture that the tests are inaccurate, when in reality the tests are accurate. What this article is looking at is called the "sensitivity" of a test: https://en.wikipedia.org/wiki/Sensitivity_and_specificity
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