"Studies Skewed By Focus On Well-Off, Educated Brains"

"when the sample reflected the U.S. population, children's brains reached several development milestones much earlier.

One of these milestones involved the total surface of the brain's cortex, which plays a key role in in memory and thought. The unweighted data showed that this surface area continued to increase until after a child's 12thbirthday. The weighted data showed a much earlier peak — before age 10... 

This study doesn't look at what those differences might mean for children's emotional and intellectual development. The key point is rather that researchers should make sure that they're looking at a representative sample when they're defining "normal."

http://www.npr.org/sections/health-shots/2017/10/16/558087458/studies-skewed-by-focus-on-well-off-educated-brains?utm_source=facebook.com&utm_medium=social&utm_campaign=npr&utm_term=nprnews&utm_content=2043

FB: "It's unrealistic to expect that every brain imaging study sample represents the full range of U.S. residents, Le Winn says. But even small studies should do a better job disclosing the characteristics of people being studied. And larger studies should consider weighting the results to more accurately represent the nation's population, she says."