Indentured labour.
D000367:Age Factors; D001690:Biological Science Disciplines / Q000193:education; D002322:Career Mobility; D004651:Employment / Q000706:statistics & numerical data* / Q000639:trends; D005178:Faculty / Q000706:statistics & numerical data / Q000600:supply & distribution; D012108:Research Personnel / Q000193:education / Q000706:statistics & numerical data*; D014481:United States; D014495:Universities; D000078329:Workforce