December 13, 2014

Blaming mothers again

Q: Did you see that pregnant women are supposed to stop wearing lipstick now?

A: <sigh>

Q: But didn’t the study find lipstick lowered kids IQ?

A: What study?

Q: Um. This one that was “undertaken in the United States”

A: The United States is a big place. They’re probably doing several studies. Can you be more precise?

Q: <looks frantically for more info in the story> Um, no?

A: Perhaps you mean this paper, which is open access and easily linked.

Q: That looks right. What does it say about lipstick?

A: Nothing. The word “lipstick” doesn’t appear in the paper.

Q: You don’t need to be such a pedant. Do they call it “cosmetics” or “beauty products” or something?

A: Nope.

Q: Ok, so what is the paper about?

A: Mothers with higher exposure to some (but not others) of a class of chemicals called ‘phthlates’ had children with lower IQ scores.

Q: How much lower?

A: The average for the lowest 25% was about 7 points higher than the highest 25%.

Q: Is 7 points a lot?

A: It’s not trivial, but not huge. It’s the difference between the 60th and 40th percentile of IQ.

Q: How much uncertainty is there in that?

A: Good question. The lower limit is less than two points, the upper limit is nearly 12, but that’s assuming there wasn’t any cherry-picking in the analysis.

Q: Where does the research say phthlates come from?

A: “Exposures to phthalates are ubiquitous”. That is, they are everywhere.

Q: Not just in lipstick?

A: No.

Q: Mostly from lipstick?

A: No.

Q: If these pollutants are everywhere, could there be socioeconomic factors that affect exposure? I mean, rich people usually don’t put up with as much pollution as poor people.

A: That’s been looked at, and phthlates are one of the pollutants with environmental justice concerns, though the evidence isn’t clear on whether there’s a general socioeconomic status correlation or just a correlation with minority ethnicity.

Q: So should we worry about phthlates?

A: I don’t know. It’s not clear. It might be a good idea to reduce phthlate use in industrial processes, but it depends on what the alternatives are.

Q: Should we worry about lipstick?

A: Probably not.

Q: Should we worry about newspaper headlines blaming mothers for their children’s problems?

A: You could do worse.


Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »


  • avatar
    Simon Connell

    And then there’s this:

    “If You Microwave Plastic While Pregnant, Your Kid Might Wind Up Stupid”

    3 years ago

  • avatar
    Matías Mat

    If you go to reference 1 in the article you will find the word “cosmetics”. :)

    3 years ago

    • avatar
      Thomas Lumley

      That is true.

      However, only one of the three phthlates mentioned there in connection with cosmetics was measured in this study, and they didn’t find any associations with it. Nor had they in the past research they summarised.

      3 years ago

  • avatar
    Peter Chapman

    Let’s assume that IQ of child is correlated with IQ of mother. That is, more/less intelligent mothers tend to have have more/less intelligent children. Then the observed result could indicate that more/less intelligent mothers have more/less exposure to these chemicals. So, in performing the analysis we should adjust for intelligence of mother. Having briefly scanned the paper I don’t think this was done.

    3 years ago

    • avatar
      Peter Chapman

      Correction. Maternal IQ was one of the covariates. In fact there were a lot of covariates.

      3 years ago