Understanding the relationship between childbearing and socioeconomic status could help explain one mechanism by which the United States’ gender disparity in poverty comes to exist. However, measuring the relationship between childbearing and socioeconomic status is complicated by the very high prevalence of childbearing among women and multiple sources of endogeneity in the characteristics of childbearing that do vary. Focusing on the timing of childbearing, I use miscarriage to construct an instrument for delivery and build a counterfactual condition for having a short temporal space between births. Using this approach with data from the National Longitudinal Survey of Youth 1979, I estimate the effect on midlife poverty of having first and second births within 24 months of each other. My results indicate that these short interbirth intervals are causally related to increased midlife poverty. The results are robust to a variety of alternate specifications of counterfactual conditions and estimation methods. / text

This study investigated the reproduction and survival of Formosan macaques (Macaca cyclopis). Data on birth and death of Formosan macaques at Mt. Longevity were collected from 1996 till 2006. The birth of Formosan macaques peaked from April to June (94.4%). The sex ratio of 604 infants at birth was 1:1.2 (female to male), which was not significantly different from 1:1. The death of less than one-month-old infants accounted for 22.2% of all infant death. Infant mortality (less than 1 years old) was very high (35.2%) and no sexual difference was found (p > 0.05). Mortality of males equal or older than 6 years old (16.8-33.3%) were higher than those of females (p < 0.05). In primiparous females, most females (57.6%) gave birth at four years old. The average interbirth intervals of females after infant death within the first 3 months was 0.96 years (¡Ó 0.07, n = 23) which was significantly shorter than that after the successful rearing infants (1.02 years ¡Ó 0.09, n = 185, p < 0.05). Maternal ranks, age, infant sex ratio and troop size had no significant effect on the interbirth intervals (p > 0.05). The average interbirth intervals of high-ranking females (1.03 years) were similar to those from middle- (1.10 years) and low-ranking females (1.01 years). The average interbirth intervals after daughters were slightly longer than those after sons (1.02 and 1.01 years, prospectively). Interbirth intervals among small-sized troops (0.97 years) was slightly shorter than those from large- (1.02 years) and middle-sized troops (1.00 years). The birth rates of high- and middle-ranking females (66.3% and 68.0%, prospectively) were significantly higher than that of low-ranking females (45.6%, p < 0.05). Maternal rank and age had no significant effect on male infant ratio (p > 0.05). However, male infant ratio of high-ranking and young-aged females (76.2%) was 1.3-1.6 times of high-ranking, middle- and old-aged females, 1.5-1.7 times of middle-, low-ranking and young-aged females. Male infant ratio of middle troop size and high-ranking females (66.7%) was 1.2-1.4 times of large- and small-sized troops; 1.4-1.5 times of middle troop size and middle- and low-ranking females.