▁of ▁scar ce ▁skills ▁correl ates ▁with ▁higher ▁income . ▁ ▁The ▁" col lege ▁prem ium " ▁refers ▁to ▁the ▁increase ▁in ▁income ▁to ▁workers ▁with ▁four - year ▁college ▁degrees ▁relative ▁to ▁those ▁without . ▁The ▁college ▁prem ium ▁double d ▁from ▁ 1 9 8 0 ▁to ▁ 2 0 0 5 , ▁as ▁the ▁demand ▁for ▁college - ed uc ated ▁workers ▁has ▁exceed ed ▁the ▁supply . ▁Econom ists ▁Gold in ▁and ▁K atz ▁estimate ▁that ▁the ▁increase ▁in ▁economic ▁returns ▁to ▁education ▁was ▁responsible ▁for ▁about ▁ 6 0 % ▁of ▁the ▁increase ▁in ▁w age ▁inequality ▁between ▁ 1 9 7 3 ▁and ▁ 2 0 0 5 . ▁The ▁supply ▁of ▁available ▁gradu ates ▁did ▁not ▁keep ▁up ▁with ▁business ▁demand ▁due ▁primarily ▁to ▁increasing ly ▁expensive ▁college ▁educ ations . ▁Ann ual ▁tu ition ▁at ▁public ▁and ▁private ▁univers ities ▁aver aged ▁ 4 % ▁and ▁ 2 0 % ▁respectively ▁of ▁the ▁annual ▁median ▁family ▁income ▁from ▁the ▁ 1 9 5 0 s ▁to ▁ 1 9 7 0 s ; ▁by ▁ 2 0 0 5 ▁these ▁figures ▁were ▁ 1 0 % ▁and ▁ 4 5 % ▁as ▁colleg es ▁raised ▁prices ▁in ▁response ▁to ▁demand . ▁Econom ist ▁David ▁Autor ▁wrote ▁in ▁ 2 0 1 4 ▁that ▁approximately ▁two - third s ▁of ▁the ▁rise ▁in ▁income ▁inequality ▁between ▁ 1 9 8 0 ▁and ▁ 2 0 0 5 ▁was ▁account ed ▁for ▁by ▁the ▁increased ▁prem