> the proportion of adults without a college degree who marry plummeted from just over 70 percent to roughly 45 percent. seems to be the answer is right here -

> the proportion of adults without a college degree who marry plummeted from just over 70 percent to roughly 45 percent. seems to be the answer is right here - college. Historically the basic level of necessary education has been increasing. 4 year grammar school couple centuries ago to the K-12 30 years ago, and today it is "K-16", i.e. K-12 plus college. Not having college today is more and more like not having GRE several decades ago.