Since it is assumed, that the more gifted people achieve averagely higher levels of education, therefore, in the process of learning it is organized by the sorting of students according to their level of abilities. Another researcher - J. Psaharopulos (Psacharopoulos, 1973) - believes, that if certificates of education has been used as a filter, then persons with a complete education would have higher rates of return, than those with incomplete education, but in reality, these differences are very minor. If the filter theory is correct, then the impact of education on earnings should decrease with age, because usually entrepreneurs learn in practice the ability of workers and as a result wages may differ in accordance with real performance of employees, and not be random, evaluating only level of education.