DEMOGRAPHV© Volume 15, Number 4 November 1978 AGE, BIOLOGICAL FACTORS, AND SOCIOECONOMIC DETERMINANTS OF FERTILITY: A NEW MEASURE OF CUMULATIVE FERTILITY FOR USE IN THE EMPIRICAL ANALYSIS OF FAMILY SIZE Bryan Boulier Office of Population Research, Princeton University, Princeton, New Jersey 08540 Mark R. Rosenzweig Department of Economics, Vale University, New Haven, Connecticut 06520 Abstract-To influence the number of children ever born to a woman, socioeco- nomic variables must operate through behavioral and biological mechanisms such as the age at marriage, the level of fertility in the absence of deliberate fertility control, and the level of control exerted to reduce fertility within marriage. In this paper, we propose a new measure of cumulative fertility which is standardized for the age-fecundity relationship and for exposure to the risk of conception associated with duration of marriage. A simple model of fertility behavior which incorporates some of the mechanisms through which socioeconomic factors may affect fertility is developed and applied to data from the United States to demonstrate the properties of alternative measures of family size. The results indicate that use of the new measure allows more precise estimates of socioeconomic fertility relationships than would be obtained with children ever born or by sample stratification. INTRODUCTION To influence the number of children ever born to a woman, social and eco- nomic variables must operate through be- havioral and biological mechanisms such as exposure to intercourse, fecundity, use or nonuse of contraception, and others (Davis and Blake, 1956; Ryder, 1959; Yaukey, 1961; Easterlin, 1975; Freedman, 1975). All too often, however, many of the constraints on fertility imposed by these biological factors are ignored in both the- oretical and empirical investigations of fertility determination. For example, in many economic models the demand for own children of a newly married couple is assumed to be influenced by variables such as education and the price of the woman's time and constrained by the level of potential income (Willis, 1973; DeTray, 1973), but no account is taken of the bio- logical constraints on the supply of own children as part of the theoretical model. A number of procedures have been em- ployed to take into account some biologi- cal factors in empirical work on the de- terminants of cumulative fertility. A common method consists of the inclusion of variables such as age at marriage, dura- tion of marriage, or some combination of these variables in linear regressions of children ever born on socioeconomic vari- ables believed relevant to fertility determi- nation. Thus, for example, Ben-Porath (1973) includes age; Harman (1970) in- cludes duration of marriage; Encarnacion (1974) includes age at marriage, marriage duration, and the square of marriage du- ration; and Kelley (1976) includes age but permits the intercept of the regression and the coefficient of age to vary by age group. We show below, however, that these mod- 487 Downloaded from http://read.dukeupress.edu/demography/article-pdf/15/4/487/907772/487boulier.pdf by guest on 12 January 2023