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There is an extensive literature on the relationship between birth order and psychological traits, but no previous study has investigated the influence of ordinal position on personality development within adoptive siblings. Such a design is important because it effectively separates the effects of biological birth order and rearing order. Here we report(More)
Personality changes over time can be analyzed by the same twin and adoption methods used to analyze the genetic and environmental influences on a trait at a given time. Composite parent rating measures of Extra-version, Socialization, and Stability made on two occasions approximately 10 years apart on 229 adopted and 83 nonadopted children from the Texas(More)
An analysis of genetic and environmental contributions to intellectual change was carried out by means of a path model applied to IQ data from the Texas Adoption Project, an adoption study in which children were measured on 2 occasions approximately 10 years apart. Included in the model were assortative mating, selective placement, genotype-environment(More)
Personality test data from the California Psychological Inventory were collected on 99 pairs of identical and 99 pairs of fraternal adult male twins. Heritabilities were comuted for all 18 scales and compared to the heritabilities for "pure" scales with overlapping items omitted. Two of the pure scales, Responsibility and Femininity, had zero(More)
Adoption studies provide an opportunity to check on twin-study inferences about genetic and environmental effects on personality. The Texas Adoption Project obtained personality tests and ratings from members of 300 adoptive families: MMPIs and 16PFs for adults, and Cattell scales and parents' ratings for children. Overall there was little personality(More)
Intellectual and personality measures were available from unwed mothers who gave their children up for adoption at birth. The same or similar measures have been obtained from 300 sets of adoptive parents and all of their adopted and natural children in the Texas Adoption Project. The sample characteristics are discussed in detail, and the basic findings for(More)
Stoolmiller has recently presented a model featuring an inferred dimension of family quality which, he suggests, is severely truncated in adoption studies such as the Texas Adoption Project, resulting in gross underestimation of the effects of shared family environment. We discuss some potential limitations of his approach in general and as he applies it to(More)
Unrelated children reared together (N = 156) in 71 different families included in the Texas Adoption Project were compared for similarities on intelligence and achievement tests. The purpose was to see if a distinction between the two types of tests based on their heritabilities could be sustained. Results indicated no substantial differences in(More)