refer1 - Ekehammar, B., Akrami, N., Hedlund, L., Yoshimura,...

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Ekehammar, B., Akrami, N., Hedlund, L., Yoshimura, K., Ono, Y., Ando, J., et al. (2010). The generality of personality heritability: Big-Five trait heritability predicts response time to trait items. Journal of Individual Differences , 31 (4), 209-214. doi:10.1027/1614-0001/a000029. To explain the differential course of anxiety and depression in individuals from childhood to adulthood by examining age-related changes in the genetic and environmental etiology of anxious and depressive symptoms. Method: A sample of 1470, 1839, and 2023 Dutch twins aged 12,14, and 16 years reported on symptoms of anxious depression (AD) and withdrawn behavior (WB), using the Youth Self Report (YSR). AD and WB were analyzed with bivariate cross- sectional genetic models for each age group to obtain estimates of the relative influence of genes (A), shared (C), and nonshared (E) environment. Results: The best-fitting models revealed no difference between heritability estimates in boys and girls. Familial clustering at age 12 years was explained by genetic and shared environmental factors. At ages 14 and 16 years, genetic factors were sufficient to explain familial clustering, shared environmental effects were absent. Genetic influences on AD and WB correlated highly. Conclusions: These findings are in agreement with earlier studies on age-specific effects of genes and shared environment on anxiety, depression, and withdrawn behavior in childhood and adolescence. The current study demonstrated that the decrease in the role of shared environment occurs after age 12. Hormonal changes accompanying the onset of puberty do not seem to explain the change in risk factors, as in 90% of the subjects puberty had already started. More knowledge on age-specific risk factors may offer opportunities for therapeutic interventions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) Lamb, D., Middeldorp, C., van Beijsterveldt, C., Bartels, M., van der Aa, N., Polderman, T., et al. (2010). Heritability of anxious-depressive and withdrawn behavior: Age-related changes during adolescence. , 49 (3), 248- 255. doi:10.1097/00004583-201003000-00008. Previous studies exploring the heritability of cannabis initiation have been carried out in the United States, Australia and United Kingdom. In the present study we assess cannabis initiation in The Netherlands, where the use of cannabis in small amounts is permitted. The sample included 3115 twins with a mean age of 27.4 years (SD 4.7) who are registered with the Netherlands Twin Register (NTR). Individual differences in cannabis initiation showed moderate genetic influences (44%). The remaining variance was explained by environmental influences shared by twins (31%) and by unique environmental factors (24%). Compared to studies from other countries, these results suggest that the relative importance of genetic and environmental factors is not different in a country with a more liberal
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This note was uploaded on 10/16/2011 for the course PSYCH 101 taught by Professor Brown,b during the Spring '08 term at BYU.

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refer1 - Ekehammar, B., Akrami, N., Hedlund, L., Yoshimura,...

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