ECONOMIC

TABLE 37.—Average usual weekly earnings of male workers 35—44 years of age who worked fulltime, by years of schooling and race, 1973Years of schoolingWhiteNegro andother races0-45-789-11 .. .1213-1516Over 16$150173202211231265321333$96149165165178209241284Note.—Data are from a survey made in May 1973.A full-time worker is defined as one who usually works 35 hours or more per week.Source: Department of Labor, Bureau of Labor Statistics.One suggested reason why schooling and earnings are positively related isthat schooling increases a worker's productivity. A mobile labor force andcompetitive markets translate the increased productivity into higher incomefor the worker. To test the hypothesis that schooling increases productivityand thereby increases income, one must have some measure of productivityother than income itself. Several studies have investigated the associationbetween schooling and the productivity of self-employed farmers, as wellas the association between schooling and efficiency in household activitiesand in interregional migration, and in scores on standardized ability tests.They indicate that, controlling for other variables, those people with moreschooling are more productive.Some say that those capable of higher productivity receive more schoolingand that business firms use the amount of schooling as a means of sortingout those capable of better performance. It is therefore important to distinguishbetween schooling as a means of changing productivity and schoolingas a means of identifying the more productive members of the population.The sorting hypothesis implies that firms regard the number of years ofschooling as an index of individual qualities that the educational system canidentify more efficiently than they can. The educational system, accordingto this theory, is effective in attracting persons possessing these qualities anddiscouraging the schooling of those without these qualities. Empirical testsof the sorting hypothesis have not been conclusive.POST-SCHOOL TRAININGAnother important aspect of training is experience acquired on the jobafter schooling is completed. On-the-job training can vary from formaltraining programs within the firm to the informal process of learning bydoing. Thus, particularly at younger ages, a worker may be involved in aprocess of investment with returns accruing later on. For this reason earningswould rise as age increases.Charts 8 and 9 give the results of two different procedures to find therelation between age and income for males. Chart 8 presents the age-incomeprofiles of a group of men over time (cohort profile). For a cohort, income146