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Here's the meat: > About 40% of the nearly 600 women lived in cities with fluoridated drinking water [...]. Three to 4 years after the women gave birth, resear

by dtech 7y ago

Here's the meat: > About 40% of the nearly 600 women lived in cities with fluoridated drinking water [...]. Three to 4 years after the women gave birth, researchers gave their children an age-appropriate IQ test. After controlling for variables such as parental education level, birth weight, prenatal alcohol consumption, and household income, as well as exposure to environmental toxicants such as lead, mercury, and arsenic, they found that if a mother’s urinary fluoride levels increased by 1 milligram per liter, her son’s (but not her daughter’s) IQ score dropped by about 4.5 points. That effect is on par with the other recent studies looking at childhood IQ and low-level lead exposure. So that's an average 1.3 IQ drop in cities with fluoride. For 1 gender. In an IQ test for 4 year olds. An IQ test. Can anyone with more knowledge of statistics chime in? This feels like it cannot be statistically significant with n=600, a subgroup analysis and a test I cannot imagine being even remotely accurate (IQ test for 4 year olds)

DevX101 7y ago
Until another replicated study comes along to dispute this, I'll take the word of the author and the editors at JAMA over your 'feel' that this isn't statistically significant. "There was a significant interaction (P = .02) between child sex and MUFSG (6.89; 95% CI, 0.96-12.82) indicating a differential association between boys and girls. A 1-mg/L increase in MUFSG was associated with a 4.49-point lower IQ score (95% CI, −8.38 to −0.60) in boys, but there was no statistically significant association with IQ scores in girls (B = 2.40; 95% CI, −2.53 to 7.33)." 1. https://jamanetwork.com/journals/jamapediatrics/fullarticle/2748634 https://jamanetwork.com/journals/jamapediatrics/fullarticle/...
- dtech 7y ago
  I browsed the article and have a basic understanding of statistics, no need to get patronizing. The article does not state the variance of this IQ test and does not state how many subgroups they analyzed and whether they corrected for that or if they a-priory were planning on analyzing gender. Picking subgroups until you've found one that is statistically significant is a well known technique in P-hacking. Other problems: - The IQ score for girls is 5 points higher on average than for boys in the study group - Fluoridation has the opposite effect for girls, the average IQ was 1.5 points higher. It is really strange for a chemical to have a completely different effect on young girls and boys. Statistical variance is much more likely - The average IQ score in the sample was 107, well above the average 100 - Parent IQ was not a variable, only the very roughly correlated high school diploma or not and household income. "Extraordinary claim require extraordinary evidence", and this study seems to at best be an indication that further research is needed rather than iron-clad proof of this effect.
  - word-reader 7y ago
    It's really not that strange for a chemical to have different effects on girls and boys, anything that affects sex hormones at all or sex-specific development is going to have a different effect.
    - shawnz 7y ago
      Even in 4 year olds, though? And such that it produces the exact opposite effect compared to the control?
BookmarkSaver 7y ago
Kinda looks like p-hacking. They ran calculated the p-value for a bunch of different criteria until they found one that was "statistically significant" (in this case gender, specifically just one gender). The issue is that you'll find 5% outliers 5% of the time, so if you just keep looking you'll eventually find "significance". This would demand reproduction before action.
- Smithalicious 7y ago
  It only looks like p-hacking if you go in with the belief that the results can not possibly be correct, and even then Hanlon's Razor would make me reluctant to accuse them of p-hacking.
  - dtech 7y ago
    If an effect only occurs in a subgroup which we have no explanation for, it's a smell that different subgroups were tried until a "statistically significant" one was found by chance.
- xref 7y ago
  Why is someone raising the question of p-hacking and suggesting a replicated study is needed being downvoted?? The paper is described as “barely statistically significant” so p-hacking, which on HN we see is rampant, seems like it should be discussed
deleted 7y ago
[deleted]
notahacker 7y ago
Regardless of whether it's statistically significant in terms of p-value, its pretty hard to discount the possibility the controls might not be effectively applied (and I find the basic idea that fluoride might have adverse developmental affects on babies highly plausible). When you're comparing fluoridated and non-fluoridated areas of just six cities there are likely to be other regional effects not perfectly captured by the controls - whilst controlling for parental education they found systematic differences in the parents' education levels between fluoridated and non-fluoridated communities. And they attempted that controlling without any data for the most significant factor in child IQ - parental IQ...

by dtech 7y ago

DevX101 7y ago

Until another replicated study comes along to dispute this, I'll take the word of the author and the editors at JAMA over your 'feel' that this isn't statistically significant. "There was a significant interaction (P = .02) between child sex and MUFSG (6.89; 95% CI, 0.96-12.82) indicating a differential association between boys and girls. A 1-mg/L increase in MUFSG was associated with a 4.49-point lower IQ score (95% CI, −8.38 to −0.60) in boys, but there was no statistically significant association with IQ scores in girls (B = 2.40; 95% CI, −2.53 to 7.33)." 1. https://jamanetwork.com/journals/jamapediatrics/fullarticle/2748634 https://jamanetwork.com/journals/jamapediatrics/fullarticle/...

dtech 7y ago
I browsed the article and have a basic understanding of statistics, no need to get patronizing. The article does not state the variance of this IQ test and does not state how many subgroups they analyzed and whether they corrected for that or if they a-priory were planning on analyzing gender. Picking subgroups until you've found one that is statistically significant is a well known technique in P-hacking. Other problems: - The IQ score for girls is 5 points higher on average than for boys in the study group - Fluoridation has the opposite effect for girls, the average IQ was 1.5 points higher. It is really strange for a chemical to have a completely different effect on young girls and boys. Statistical variance is much more likely - The average IQ score in the sample was 107, well above the average 100 - Parent IQ was not a variable, only the very roughly correlated high school diploma or not and household income. "Extraordinary claim require extraordinary evidence", and this study seems to at best be an indication that further research is needed rather than iron-clad proof of this effect.
- word-reader 7y ago
  It's really not that strange for a chemical to have different effects on girls and boys, anything that affects sex hormones at all or sex-specific development is going to have a different effect.
  - shawnz 7y ago
    Even in 4 year olds, though? And such that it produces the exact opposite effect compared to the control?

BookmarkSaver 7y ago

Kinda looks like p-hacking. They ran calculated the p-value for a bunch of different criteria until they found one that was "statistically significant" (in this case gender, specifically just one gender). The issue is that you'll find 5% outliers 5% of the time, so if you just keep looking you'll eventually find "significance". This would demand reproduction before action.

Smithalicious 7y ago
It only looks like p-hacking if you go in with the belief that the results can not possibly be correct, and even then Hanlon's Razor would make me reluctant to accuse them of p-hacking.
- dtech 7y ago
  If an effect only occurs in a subgroup which we have no explanation for, it's a smell that different subgroups were tried until a "statistically significant" one was found by chance.
xref 7y ago
Why is someone raising the question of p-hacking and suggesting a replicated study is needed being downvoted?? The paper is described as “barely statistically significant” so p-hacking, which on HN we see is rampant, seems like it should be discussed

deleted 7y ago

[deleted]

notahacker 7y ago

Regardless of whether it's statistically significant in terms of p-value, its pretty hard to discount the possibility the controls might not be effectively applied (and I find the basic idea that fluoride might have adverse developmental affects on babies highly plausible). When you're comparing fluoridated and non-fluoridated areas of just six cities there are likely to be other regional effects not perfectly captured by the controls - whilst controlling for parental education they found systematic differences in the parents' education levels between fluoridated and non-fluoridated communities. And they attempted that controlling without any data for the most significant factor in child IQ - parental IQ...