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In 1970, just 1 in 5 U.S.-born PhD graduates in economics had a parent with a graduate degree. Now? Two-thirds of them do, according to a new analysis from the Peterson Institute for International Economics. The trends are similar for other fields (and for foreign-born students), but economics is off the charts.> This partly reflects population trends: Over that same period, the share of parents with graduate degrees and college-age children rose 10 percentage points, to 14 percent, our analysis of Census Bureau data shows. But compared with the typical American, a typical new economist is about five times more likely to have a parent with a graduate degree.
So % of parents with college degree increased by 3.5x (from 4% to 14%) and % of students coming from parents with college degree increased 3.3x (from 1/5 to 2/3). That more than explains it, doesn't it?
Also there should be a high correlation between kids being college-material and parents being college-material. Whether you believe in nature (genetics) or nurture (good parenting, high standards, role model, access to education, etc), or a mix of both, either way, you should not expect the % of college students from graduate families to match the % of graduate families in the country. So not sure what point the article makes.