In “”Relative Cohort Size: Source of a Unifying Theory of Global Fertility Transition?” Diane Macunovich asserts that Richard Easterlin’s theory of relative cohort size may be the missing link in his supply-demand theory of fertility transition in preindustrialized societies (developing countries). Easterlin’s supply-demand theory of fertility transition states that periods of excess demand for children and periods of excess supply of children alternate back-and-forth about five times before a rough equilibrium between demand and supply are achieved. Demand for children is typically very high at the outset of fertility transition in preindustrialized societies because mortality rates and rates of involuntary infecundity are high. Easterlin’s supply-demand theory of fertility transition predicts that as mortality rates and involuntary infecundity rates decline, the excess demand for children becomes an excess supply of children. Then, the potential for an even greater excess supply of children prompts fertility-control behaviors among members of the preindustrialized society (contraception, marriage later in life, etc.). Macunovich believes that Easterlin’s theory of relative cohort size provides a valid explanation for why the demand for children declines when it does – essentially 15 to 20 years after the infant mortality rate declines.
Macunovich points out that previously determined factors of the decline in the demand for children are “necessary” rather than “sufficient” conditions for fertility reduction. For example, a reduction in infant mortality or an increase in the net cost of children and economic development are events which must occur in order for the demand for children to decline. In turn, Macunovich speculates that an increase in relative cohort size (RCS) is an event which can occur and can subsequently initiate the decline in demand for children. Thus, increasing RCS is the primary cause of fertility reduction according to Macunovich. Her discovery of a “robust” relationship between relative income and fertility and an “asymmetrical” relationship between RCS and relative income are what spawned this hypothesis.
In data provided by the United Nations, Macunovich found that a reduction in infant mortality did not spur a reduction in fertility until the infant mortality reduction and accompanying fall in mortality rates of children and young adults permitted the proportion of the population aged 15-24 to rise relative to those aged 25-59. This trend applied to more than 100 countries that had begun the process of fertility transition 50 years prior to the publication of Macunovich’s essay. Macunovich speculates that the reason for this lag in fertility reduction was the need for members of the new, larger cohort to experience the effects of an asymmetrical relationship between RCS and relative income. Only when members of the larger cohort entered the labor market and tried to earn a living were the effects of their size compared to the size of previous cohorts felt. In the market for employment, members of the larger cohort found themselves competing with not only more workers, but older and more experienced workers, for jobs. Thus, they received smaller wages and earned less income relative to their parents and members of the previous generation. This decline in relative income is what urged many members of the new, large cohort to delay marriage and/or reduce fertility in order to maintain a higher level of per capita disposable income.
Macunovich offers the additional hypothesis that Third World people’s voluntary decision to reduce fertility under conditions of high RCS and low relative income is evidence of a preindustrialized society becoming more modern and more developed. Thus, in her essay, she not only speculates that a theory commonly applied to fertility transition in developed countries (the theory of relative cohort size) could be applied to fertility and demographic transition in developing countries; Macunovich also speculates that this theory could explain why developing countries become developed as they go through the process of demographic transition.