In the 1960s he and Jacob Mincer developed the New Home Economics, of which Becker's theory of allocation of time is a centerpiece. Becker argued that such decisions are made in a marginal-cost and marginal-benefit framework and that marriage markets affect allocation into couples and individual well-being. His research examined the impact of higher real wages in increasing the value of time and therefore the cost of home production such as childrearing. As women increase investment in human capital and enter the workforce, the opportunity cost of childcare rises. Additionally, the increased rate of return to education raises the Desire to provide children with formal and costly education. Coupled together, the impact is to lower fertility rates. His theory of marriage was published in 1973 and 1974. Among its many insights are that (1) sex ratios (the ratio of men to women in marriage markets) are positively related with wives' relative access to consumption in marriages and (2) men with higher incomes are more likely to be polygamous. He published a paper on divorce in 1977, with his students Robert T. Michael and Elizabeth Landes, hypothesizing that divorces are more likely when there are unexpected changes in income. Many of these insights on fertility, marriage, and divorce were included in Becker's A Treatise on the Family, first published in 1981 by Harvard University Press.