Differences in human capital $($for example, $$ lead to differences in individual earnings. According to a recent Current Population Survey, the median usual weekly earnings of $25-$and$-$over workers with only high school diplomas were $q,$ the earnings of a worker with a Master's degree. The $q,$ marginal product of workers that have invested heavily in their own human capital helps to create high demand for their skills.

more than double ${?}^4$

approximately half ${?}^4$ about $$1000$ less than $*$

higher ${?}^{+}$