根据Mincer(1974)的工资模型规范，Card(1999)提出了两种假设，以对教育的真实回报进行有意义的评估。首先，他断言，在标准的人力资本收益函数中，教育变量是在使用完成教育的年数时被正确度量的，而不是始终作为分类变量度量的个人教育水平。其次，他指出，在其他条件相同的情况下，一年的教育增长应该以同样的幅度影响收入。如果满足上述两个条件，那么我们就可以精确地估算出学校教育的真实回报(Card, 1999)。前面的讨论表明，受过良好教育或有多年工作经验的人被认为是高效的，因此会得到经济上的回报。人力资本模型的支持者(Becker, 1964)和(Mincer, 1974)认为，一个人受教育一年的回报率等于他的工资随时间的折现价值。因此，当且仅当内部收益率超过上学的边际成本时，一个人继续他/她的教育是重要的。文献中的许多实证研究都证实了知识存量的积累和工人多年经验的增加是如何导致工资增加的。例如，Day和Eric(2002)提供的证据表明，高中毕业生的年收入比大学毕业生低三分之一左右。
Following Mincer’s (1974) wage model specification, Card (1999) posits that two hypotheses must hold to allow a meaningful assessment on the true return to education. First, he asserts that in the standard human capital earning function, the education variable is measured correctly when the number of years of completed education is used rather than the individual’s level of education which is always measured as a categorical variable. Secondly, he points out that a year increase in education should affect earnings by the same magnitude, other things being equal. If the two conditions above are satisfied, then one can estimate the true returns to schooling with precision (Card, 1999). The previous discussions indicate that a person who is well-educated or has more years of experience on a job is expected to be efficient and is therefore rewarded financially. Proponents of the human capital model, (Becker, 1964) and (Mincer, 1974) are of the view that the rate of return at a person’s year of education is equivalent to his discounted value of wages over time. It is therefore important for a person to continue his/her education if and only if the internal rate of return outstrips the marginal cost of schooling. Many empirical works in the literature have confirmed how the accumulation of stock of knowledge and the increase in the years of experience of a worker have resulted in an increased wage. For instance, Day and Eric (2002) provide evidence that the annual earnings of a high school graduate were about one-third lower than the earnings of a college graduate.