Investigates relationships between family structure variables and 17 measures describing children's intellectual, psychosocial, and physical growth. Subjects were a 10 percent random sample of a Danish cohort consisting of children born in a Copenhagen hospital between September 1959 and December 1961; 857 subjects were followed to age 19.…

Describes why birth order interests both parents and researchers, discussing what really causes apparent birth order effects on intelligence, examining problems with using cross-sectional intelligence data, and noting how to move beyond cross-sectional inferences. Explains the admixture hypothesis, which finds that family size is much more…

Critiques recent research on the effects of birth order on intelligence and personality, which found that the between-family design revealed that birth order negatively related to intelligence, while the within-family design revealed that birth order was unrelated to intelligence. Suggests that it may not be intelligence that co-varies with birth…

Critiques Rodgers et al.'s June 2000 research on the relation between birth order and intelligence, which suggests that it is a methodological illusion. Explains how the intellectual environment and the teaching function (whereby older children tutor younger ones) contribute to the growth of intellectual maturity, the first negatively and the…

A confluence model is developed that explains the effects of birth order and family size on intelligence. (Editor)

Theoretical predictions, based on the confluence model, were made for data from six national surveys of intellectual performance, each relating intellectual performance scores to family configuration variables. The confluence model was capable of accurate prediction in all cases when three parameters were estimated. (Author/RD)

Discusses the research debate over the question whether intelligence diminishes as a function of birth order. Presents a study of Zimbabwean children confirming the general downward trend of intelligence as a function of birth order. Addresses the influence of family size. (DB)

Discusses the controversy of the relationship between birth order and intellectual performance through a detailed evaluation of the confluence model which assumes that the rate of intellectual growth is a function of the intellectual environment within the family and associated with the special circumstances of last children. (CM)

Introduces the confluence model as a theory specifying the process by which the intellectual environment modifies intellectual development. Using this model, explores the contradiction between prediction of secular trends in test scores by trends in aggregate birth order and the lack of prediction of individual test scores by birth order using…

A brief review of the psychological literature on the characteristics of only children is presented in order to determine if the one-child family should be avoided or advocated. The relevant literature is found to be limited in quantity and conceptualization of the only child. Previous literature is divided into three types of study: those with…

Examined the intellectual development of 74 preschool children for contributions of family size, birth order, socioeconomic status, ethnicity, and parent-child relationships. Found that socioeconomic status and warmth of the father-child relationship made significant, positive contributions to children's intellectual development. Found support for…

Support for the confluence model of intellectual development has come from analyses of family size-birth order means of large aggregate data sets. Analyses of individual scores do not substantiate the confluence model, as explained variance is markedly reduced. The study of family interaction variables utilizing longitudinal data is recommended.…

Birth order effects on intellectual performance show both positive and negative results. Considers the intellectual aspects of siblings' changing environments, explaining that birth order and family size effects depend crucially on the age at which children are tested. Within-family data conceal patterns of aggregate effects that are revealed by…

Declining family size plus the widespread belief that only children experience adjustment difficulties provided the impetus for this investigation comparing the characteristics of only children with children raised in multiple-sibling families. Results indicated that being reared as an only child actually provided a slight developmental advantage…