A Longitudinal Study of the Effects of the Birth of a Sibling during the First 6 Years of Life

Abstract

We investigate links among the birth of a new infant, changes in the family environment, changes in the relationship between the mother and an older child, and changes in an older child's cognitive and socioemotional development. We hypothesize that the effects of sibling birth are mediated by the associated changes in the family environment and changes in the interaction patterns of the family members. Data from the National Longitudinal Survey of Youth are used on a cohort of nonminority children between 6 and 23 months old. The birth of a sibling results in significant changes in the family environment. At the same time, positive interactions with the older child diminish, especially if the birth interval is short, and the mother increasingly adopts controlling parenting styles. These changes result in lower levels of verbal development. About 2.5 years after the sibling birth, negative effects are detected on achievement and on socioemotional adjustment. Some positive effects of sibling birth also are noted on verbal ability and peer relations. Key Words: achievement, preschool children, sibling, socioemotional problems. JEANNE BROOKS-GUNN Columbia University* This study investigates the changes in the level of cognitive and socioemotional development after the birth of a sibling in a national cohort of infants and toddlers over a 4-year period. Previous studies relied on detailed data obtained from interviews and observations of small samples. These studies examined the prenatal and postnatal patterns of interaction among family members (Dunn & Kendrick, 1980; Dunn, Kendrick, & MacNamee, 1981; Dunn & Munn, 1985; Kendrick & Dunn, 1982; Stewart, 1990; Stewart, Mobley, Van Tuyl, & Salvador, 1987). They contribute to our understanding of the birth of a sibling as a process of adjustment in the family system that leads to some positive and some negative, outcomes for the older sibling. Generally, the quality and intensity of maternal interactions with the firstborn decrease after the birth of a sibling, and some specific behavioral and emotional problems-such as regression, anxiety, and aggression-in the older child are observed (Dunn & Kendrick, 1980; Stewart, 1990; Stewart et al., 1987). Sibling rivalry and the resulting behavior problems also have been studied (DelGiudice, 1986; Dunn & Munn, 1986; Jalongo & Renck, 1985; Pietropinto, 1985; Stewart et al., 1987). Most of these studies point to the importance of positive parenting styles in attenuating the sibling rivalry (Dunn & Munn, 1986; Gottlieb & Mendelson, 1990). They also show that the effects of sibling birth depend on age (Gibbs, Teti, & Bond, 1987; Stewart et al., 1987) and the sex of both siblings (Austin, Summers, & Leffler, 1987; Kendrick & Dunn, 1982). These studies of family processes after the birth of the second child are difficult to generalize for two reasons. First, the small samples of fewer than 100 families, often of middle-class origin and with two biological parents, may not be representative of the general population. Second, some of these study samples do not include families who did not experience the birth of a new baby. Hence, maturational changes cannot be distinguished from the changes attributed to the sibling birth (Stewart et al., 1987). Sociological studies that use large and diverse samples generally focus on the correlates of sibling group size, birth order, and birth spacing, rather than family changes after the birth of a sibling. These studies have three major shortcomings. First, sibling group size effects, holding constant the birth order, are equivalent to a study of aggregate outcomes of experiencing a number of births of siblings. This is a problem because the effects of the birth of a sibling cannot be distinguished from the effects of family size. Second, due to the limitations of cross-sectional data, neither the processes that account for sibling group size differentials, nor the factors that account for the differences in sibling group size effects (such as the age of the child at the time of sibling birth) can be fully studied. …