Fluoridation is in the news again. Because of that, I want to remind people of three things.
First, the observational evidence is usually so bad that if it convinces you of anything, that's a personal indictment.
Second, until recently, we only had one causally-informative study of reasonable levels of exposure, and it did not suggest harms and, in fact, suggested benefits.
Third, the second credible causally-informative study did not find much in the way of harms with exposure levels that were usually much greater than in the first study.
There is a widespread myth that the obesity epidemic started in or around 1980.
This is based on a misunderstanding of the relationship between body fat percentage and BMI, which is used to classify someone as "obese".
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You can see this nonlinearity replicate in numerous contexts.
For example here it is in the Heritage Family Study.
The distribution of BMIs shifts right as bodyfat percentages increase across the distribution, but the mean and variance increase faster than body fatness does due to that nonlinearity, which shows up because it's part of how BMIs are constructed.
Attempts to explain the obesity epidemic through contamination, toxins, conspiracies, seed oils, sugar, high-fructose corn syrup, lithium, or whatever else always strike me as annoying.
What we must explain is an increase of ~200-350 calories a day in energy balance. That's all.
Many papers have noted this.
They've produced helpful diagrams like:
And like this, showing that what must be explained is a small, daily surplus of calories:
I simulated 100,000 people to show how often people are "thrice-exceptional": Smart, stable, and exceptionally hard-working.
I've highlighted these people in red in this chart:
If you reorient the chart to a bird's eye view, it looks like this:
In short, there are not many people who are thrice-exceptional, in the sense of being at least +2 standard deviations in conscientiousness, emotional stability (i.e., inverse neuroticism), and intelligence.
To replicate this, use 42 as the seed and assume linearity and normality
In Singapore, they use corporal punishment so that captured criminals can be rapidly released. When criminals are caned, kidney pads are attached to them, they're tied to a trestle, and then they're struck with a hard rod.
Graffiti? Eight strikes.
You just vandalized a set of walls and you've been given the choice between two punishments.
First choice: Go to prison for one year.
Second choice: Received 24 hits from the cane.
What do you personally choose?
Which option do you believe that other good people who stupidly got involved in a crime would pick?
Male and female biology PhDs without children are similarly likely to have tenure-track jobs after they receive their PhDs.
Males may get slightly ahead, but not enough to explain the sex gap in tenure🧵
To understand the larger gap in tenure-tracking, we have to look at the group of biology PhDs with children.
For men, their odds of of being in a tenure-track position just keep going up with the years.
For women, their odds plateau after having kids.
This comparison is subject to some confounding, but you can nevertheless see that the impact of a child on the gap is timed to when the birth of the child happens, suggesting that it really is a causal impact of having a kid.