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Comment by aydyn | Hacker News Reader

> Yes you can, because they're all small effects,

"A doubling of perfluorooctane sulfonate (PFOS) in maternal serum was associated with a 39% (p < 0.001) reduction in diphtheria antibody concentration in children (age 5 yr), with increased odds of falling below clinically protective values against diphtheria and tetanus at age 7 yr."

> A study of heavily exposed workers (n = 462, geometric mean serum PFOA of 4048 ng/mL) detected significantly increased incident mortality for cirrhosis (relative risk = 3.87, 95% CI 1.18–12.7) and liver cancer (relative risk = 6.69, 95% CI 1.71–26.2)

These are NOT small effects. These are strong p-values with large hazard ratios over and over again throughout the entire review.

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(relative risk = 3.87, 95% CI 1.18–12.7) and liver cancer (relative risk = 6.69, 95% CI 1.71–26.2)

I have no domain knowledge here but those CIs are quite large and both get close to 1 at the lower edge.

Without having read the study, but going on experience reading other studies of this general type, that’s a common pattern with CIs derived from predictors in logistic regression-like models (which are often used for this kind of analysis)- the CI calculations often end up having a log in there somewhere which results in higher tails. And a RR of 1.7 is still nothing to sneeze at depending on the base rate of whatever is being discussed…

But again, I haven’t read the paper! Just chiming in with some half-forgotten epidemiology. :-)

What is this biased way of reading CIs? Are you paid by 3M?

Yes, it shows that with 5% probability the risk is only 1.18 - why choose to focus on those 5%? According to the study there is an equal chance that the relative risk is 12.7 times normal, why should we ignore that?

You really think pointing out how large a CI is, is "biased"?

Your reading of the CIs is off. It isn't telling you that there's a 5% chance that the real risk is 1.18. It's saying there's a 5% chance the real risk doesn't lie in the CI, and could be anywhere outside the CI, including 1 (no effect).

Here's the main point. Increase the significance level slightly, say to 97% (if this is a 95% CI, or 92% if this is a 90%, etc). Then a CI that large and that close to 1 at the left edge will turn into a CI that includes 1. The effect is not significant at all at that level. It wouldn't be saying the true effect is significant with some probability or whatever you seemed to be interpreting CIs to say. It would be saying there's no effect.

This is markedly different from the case of cigarettes, where the p-values are astronomically small. Since earlier comments seem to compare these chemical to cigarettes.

> A study of heavily exposed workers

Those are a very small part of the affected ones, probably firefighters or 3M production workers. Remember that the dosage makes the poison.

They're not small values, but where are the real-life effects? Last I checked diphtheria levels in Western world remain at single digits per year levels, and the rare exceptions are almost invariably antivaxxers, not because the DPT vaccine has stopped working.

…Exactly because we put a stop to it, before higher levels became more prevalent.

Or are you going to argue about how antibodies work?

We've been using PFAS for 80 years now. Are the children of heavily exposed people actually contracting diphtheria or tetanus at measurably higher rates?

Again, the headline figure you're quoting sounds alarming, but if it's accurate and applicable to the broader population, then we should be seeing that effect outside the lab as well.

> We've been using PFAS for 80 years now. Are the children of heavily exposed people actually contracting diphtheria or tetanus at measurably higher rates?

Should we wait for that to happen if the risk is obvious?

Don't the kids of mothers heavily exposed wind up deformed?

Entirely possible, but that's quite different from them being more vulnerable to diphtheria, which was the specific claim made earlier in this thread.

Youre really going to bat for this? Incredible.

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