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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Behavior genetics 22 (1992), S. 253-264 
    ISSN: 1573-3297
    Keywords: growth curves ; biometrical analysis ; Dutch Twin Register
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Longitudinal data for height (length) between birth and 2 years of age were examined for 690 Dutch Registry twin pairs. A two-stage analysis was performed, where individual growth curves were first fit to available data for each subject using a linear multiple regression procedure and estimated individual growth curve parameters were then subjected to multivariate biometrical analysis. Quadratic polynomial curves were found to adequately represent observed growth patterns for the majority of cases (median R2=.98). A specific scalar model of sex limitation best characterized individual variation in growth curve parameters. That is, there was significantly greater genetic variation for boys than for girls in both the predicted length and rate of growth at 1 year of age and the amount of deceleration in individual growth curves across age.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Behavior genetics 24 (1994), S. 357-364 
    ISSN: 1573-3297
    Keywords: Assortative mating ; spouse similarity ; attitudes ; personality ; psychological well-being ; convergence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract The study of the origin of spouse similarity is interesting because the extent to which spouse similarity reflects genetic resemblance between husbands and wives affects the genetic structure of a population. The sources of observed spouse similarity in attitudes, personality, and psychological well-being are discussed. Analyses based on data collected from an American adult sample assessed longitudinally showed that spouse correlations were high for attitudes and low to moderate for personality and psychological well-being. Four competing explanations to spouse similarity were compared: initial similarity, attrition, convergence, and age covariation. The results did not support the latter three explanations, indicating that initial similarity may be an appropriate interpretation of observed spouse similarity. The findings are consistent with those of other comparable studies.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Behavior genetics 26 (1996), S. 123-133 
    ISSN: 1573-3297
    Keywords: Attitudes ; contact ; twin similarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract The nature of the relationship between social contact and attitude similarity between twins was investigated using longitudinal data from a sample of Australian twins. Earlier research has suggested that social attitudes are not explained solely by shared environment; rather there are both genetic and environmental components that explain variance in social attitudes. Using three types of analyses we investigated the magnitude of the relationship and the direction of causation between attitude similarity and social contact. Longitudinal analysis of within-pair variance by level of contact suggests that attitude similarity leads to contact among the females and that similarity is both genetically and environmentally based. Analyses using a crosslag regression model suggest that similarity causes contact among MZ females. Biometrical analyses indicate differences in direction of causation for males and females. Among females, both genetic and shared environmental parameter estimates could be equated across contact groups, suggesting little relationship between contact and similarity. Among males, findings of smaller estimated heritability in the high-contact group suggest that similarity causes contact. However, an increased estimate of the contribution of shared environmental variance in the high-contact males could additionally suggest that contact leads to similarity.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Behavior genetics 21 (1991), S. 351-367 
    ISSN: 1573-3297
    Keywords: reaction time ; information processing ; intelligence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract This study examined the contributions of genetic and environmental factors to the observed correlation between intelligence test scores and speed of information processing, based on data for same-sex adult twin pairs (age, 15–57). Verbal and performance IQ scores from the Multidimensional Abilities Battery, as well as 11 reaction-time measures derived from a battery of information-processing tasks, were available for 50 monozygotic and 32 dizygotic pairs of twins. Multivariate biometrical analyses were used to estimate genetic and environmental parameters underlying observed variances and covariances among intelligence test scores and a general speed of information-processing factor (based on a linear composite of the 11 reaction-time scores). A common-factor model with loadings on general speed of processing, verbal IQ, and performance IQ fit the data well. The common factor was influenced primarily by additive genetic effects, such that the observed relationships among the speed and IQ measures are mediated entirely by hereditary factors. There was additional specific genetic variance for Verbal IQ and specific shared-twin environmental variance for Performance IQ. However, twin similarity for general speed of processing was explained entirely by genetic factors related to intelligence. The results emphasize the importance of common, heritable, biological mechanisms underlying the speed-IQ association.
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  • 5
    ISSN: 1573-3297
    Keywords: Phenotypic assortment ; social homogamy ; delta paths ; twins ; education ; intelligence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Phenotypic assortment is assumed to be the principal mechanism of spouse similarity in most biometrical studies. Other assortment mechanisms, such as social homogamy, may be plausible. Two models are presented that consider phenotypic assortment and social homogamy simultaneously (i.e., mixed assortment), where selective associations between social background factors (Model I) versus selective associations between total environments (Model II) distinguish the models. A series of illustrative analyses was undertaken for education and fluid ability available on a sample of 116 Swedish twin pairs and their spouses. On the basis of several fit criteria Model I was preferred over Model II. Both social homogamy and phenotypic assortment may contribute to spouse similarity for educational attainment and fluid ability. Furthermore, spouse similarity for fluid ability may arise indirectly from social homogamy and phenotypic assortment for educational attainment. Power analyses indicated greater observed power for Model I than Model II. Additional power analyses indicated that considerably more twin-spouse sets would be needed for Model II than Model I, to resolve social homogamy and phenotypic assortment. Effects of misspecification of mechanisms of spouse similarity are also briefly discussed.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Behavior genetics 30 (2000), S. 41-50 
    ISSN: 1573-3297
    Keywords: Structural equation modeling ; survival analysis genetically informative data ; power ; Type I error
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Recently a new method for the analysis of survival data using a structural equation modeling approach has been suggested by Pickles and colleagues using twin data they demonstrated the application of this model to study the correlation in age of onset. The purpose of the current research is twofold: 1) to evaluate the statistical performance of the model as presented by Pickles and colleagues, and 2) to expand and evaluate the model in more applications, including both genetically informative data and other multivariate examples. Results evaluated from this study involve three areas of method performance: Type-I error rates, power, and parameter estimates under four different distributions (normal, Gamma-2, Gamma-6 and g-and-h) and four different sample sizes (n = 125, 250, 500 and 750). Results based on the original Pickles model indicated that in all sample size and distribution conditions the Type-I error rate was adequate, in fact below the nominal level of .05. Additionally, power was greater than .80 for sample sizes of 500 or more for all distribution conditions. Parameter estimates were upwardly biased when the population value was ρ = .20. This bias varied across distributions; the g-and-h distribution showed the largest bias. Results from the expanded model indicated that Type-I error rates were adequate. Power results were not affected by distribution type; sample sizes of 500 were above the .80 level. Parameter estimates continued to be upwardly biased in this more general model, although the degree of bias was smaller.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-3297
    Keywords: Wechsler IQ ; Colorado Reading Study ; Covariance structures ; twins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract This study is the first analysis of the etiology of the relationship between general intelligence and speed of cognitive processing. The genetic and environmental sources of this covariation were examined using data from 60 pairs of twins (30 monozygotic and 30 same-sexed dizygotic), ages 8–18. Full-Scale IQ scores on the Wechsler Intelligence Scale for Children-Revised (WISC-R) served as an index of general intelligence. Measures of speed of processing employed were the Rapid Automatic Naming tests and Colorado Perceptual Speed tests. Results of multivariate biometrical genetic analyses revealed the importance of genetic influences underlying the IQ/speed association. The relative importance of correlated genetic effects, however, appeared to be dependent upon the specific speed-of-processing measure. Our results indicate that the phenotypic relationship between the measures of general intelligence and the measures of speed of processing employed are due largely to correlated genetic effects. While correlated specific environmental effects were less important, correlated common environmental effects were negligible. In general, the findings support the notion of some common biological mechanism(s) underlying both general intelligence and speed-of-processing measures.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Behavior genetics 19 (1989), S. 355-370 
    ISSN: 1573-3297
    Keywords: Sex differences ; liability ; adoption study ; property criminality ; threshold
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Sex differences in genetic and environmental influences on criminal behavior against property were studied in a birth cohort of 6129 male and 7065 female Danish adoptees and their biological and adoptive parents. Both genetic and environmental factors were found to contribute to variation in liability to property criminality, the relative proportions of variance explained being similar in males and females. Important shared- and nonshared-family environmental factors were present. In separate analyses of average liability toward property criminality, however, convicted females appeared to be more genetically predisposed than convicted males, a conclusion based on the finding that female property offenders were more likely than male offenders to have convicted biological (but adopted-away) offspring. On the other hand, property-offending males and females did not appear to differ in their average shared-family environmental liabilities, since conviction rates did not differ for adoptees of convicted adoptive mothers and fathers. Also, social class in the adopitive parents of convicted sons and daughters were comparable, further indicating that average shared-family environmental liabilities do not differ between the sexes.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-3297
    Keywords: Educational attainment ; Australian twins ; sex differences ; secular changes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract The relative effects of genetic and environmental factors in producing individual differences in educational achievement are compared across women and men and over birth cohorts. In a large sample of Australian twin pairs, the heritability of self-reported educational attainment did not vary among women and men born before and after 1950. In a “psychometric” model of twin resemblance, based on separate self-reports in 1981 and 1989, genetic factors explained 57% of the stable variance in educational achievement, while environmental factors shared by twins accounted for 24% of the variance. Corrections for phenotypic assortative mating for educational level, however, suggested that estimated common-environmental effects could be entirely explained by the correlation between additive genetic values for mates. Taking this into account, heritability of “true” educational attainment in Australia may be as high as 82% with the remaining variation being due to individual environments or experiences. Unlike previous studies in Scandinavian countries, results in Australia suggest that factors influencing educational success are comparable between women and men and for individuals born at different points during this century.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1573-3297
    Keywords: Mate selection ; social homogamy ; phenotypic assortment ; delta paths ; twins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Genetic influences have consistently been reported to be the principal explanation for resemblance among relatives for intelligence, with shared environmental effects playing a much smaller role. However, crucial to understanding the nature of environmental influences are the mechanisms of assortative mating. Phenotypic assortment, albeit widely assumed or modeled in biometrical analyses, may be less important than other assortment processes, such as social homogamy. Consequently, effects of shared environment may play a greater role than prior studies have suggested. The goal of this study was to resolve environmental and genetic influences on fluid ability based on alternative models of assortment by examining the similarity of monozygotic (MZ) and dizygotic (DZ) twins and their spouses. Raven's Progressive Matrices scores were available from a populationbased Swedish sample of 138 twin kinships. The effects of both social homogamy and phenotypic assortment were tested simultaneously in each of two alternate assortment models. A factor/delta path model represented social homogamy as a common factor and phenotypic assortment as a delta path, while a delta/delta path model represented both social homogamy and phenotypic assortment as delta paths. Overall, the factor/delta path model was found to be superior. Results suggested that social homogamy completely explained spouse similarity; phenotypic assortment was not significant. The results of these analyses suggest the presence of shared environmental effects among twinsand their spouses, which would have been underestimated if only phenotypic assortment had been assumed. Therefore, previous studies which have traditionally modeled phenotypic assortment may have underestimated the effects of shared environment.
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