> Their analyses also systematically controlled for sex, age, height, socioeconomic status, and population structure, measured using the participant's genetics.

> Their analyses also systematically controlled for sex, age, height, socioeconomic status, and population structure, measured using the participant's genetics. I’m a woefully unqualified armchair researcher/statistician, but I always enjoy speculating on potential confounding variables that weren’t controlled for. As the article mentions, there is an obvious naive candidate explanation for why people with larger brains would be smarter (more computing hardware). But I find it fun to guess at reasons there might not be a causal relationship. It’s nice to see the researcher doing the same exercise: > "However, things could be much more complex in reality. For example, consider the possibility that a bigger brain, which is highly heritable, is associated with being a better parent. In this case, the association between a bigger brain and test performance may simply reflect the influence of parenting on cognition. We won't be able to get to the bottom of this without more research." I wonder what exactly is meant there. Is he speculating that a larger brain directly provides better parenting ability? Or that perhaps generations ago a family with a useless gene that causes large brains also happened to have another unrelated gene that gave them better parenting abilities, and thus both genes ended up being reproduced a lot? How would you even control for this? Maybe adopted children?