Note that these add up to more than 100% because they are cumulative; e.g. it is assumed that all people with doctorates also have undergraduate and high school degrees, and are thus counted twice in the "lower" categories. It is not assumed, however, that all doctorates or professional degrees have Master's degrees. Age 25 is used rather than age 18 because there are few people aged 18 or over with advanced degrees. “Educational Attainment in the United States: 2018”. U.S. Census Bureau (2020年4月17日). 2020年10月28日閲覧。
