#Lost twins achievements manual

Most twin studies of reading suggest minimal contribution of shared environmental factors. Behavioral geneticists distinguish between shared environmental factors (i.e., those environmental factors that are shared by reared-together siblings and consequently contribute to their behavioral similarity), and non-shared environmental factors (i.e., those environmental factors that differ among reared-together siblings and thus do not contribute to their behavioral similarity).

Yet the nature of these environmental influences is unclear. Broadly speaking, these questions concern the magnitude of shared-environmental influence, and the existence of gene-environment interaction effect.įirst, even if substantial, heritability estimates for reading are typically far less than unity, implicating the contribution of environmental factors. Nonetheless, several important questions about the behavioral genetics of reading remain largely unresolved. It has additionally proved useful in providing a basis for efforts to identify the specific genetic factors that influence reading ( Grigorenko, 2009). Importantly, not only are reading disability and reading abilities substantially heritable, but the influence of genetic risk factors for reading disability appears to be of comparable magnitude to those that contribute to individual differences in reading-related phenotypes throughout the normal range ( Bates, et al., 2007 Hawke, Wadsworth, Olson, & DeFries, 2007).īehavioral genetic research has established the heritability of reading-related phenotypes. ( Zurnberge, Baker, & Manis, 2007) reported a heritability estimate of 70% for reading as assessed by subtests from the Woodcock–Johnson Tests of Achievement. Finally, in a community based sample of 605 pairs of twins age 10 years, Zurnberge et al. Similarly, in a sample of 440 twins age 8 to 18, Gayán and Olsen ( Gayan & Olson, 2003) reported heritability estimates of 80% or higher for 4 different measures of reading performance (e.g., word recognition, phonological decoding). ( Harlaar, Dale, & Plomin, 2007) reported that genetic factors accounted for approximately 60% of the variance in teacher-rated reading achievement at ages 7, 9 and 10. For example, in a sample of more than 4000 pairs of British twins assessed longitudinally, Harlaar et al. Analysis of twin samples unselected for reading problems have generally reported similar findings of strong heritable effects. Analysis of twin samples selected for reading problems or disability (reviewed by Grigorenko, 2004) indicate that roughly 50-70% of variance in reading problems is associated with genetic factors. There is a substantial and consistent behavior-genetic literature implicating the existence of genetic influences on reading abilities and disability. Finally, we explore whether the reading ability and education level of parents moderates the degree to which genetics, or the shared environment, shape the reading ability of their offspring. We estimate the degree to which genetics versus the shared environment (which comprises family context, neighborhoods, schools, etc.) contribute to reading achievement and reading disability. The present study is an attempt to further understand individual differences in reading achievement and the etiology of reading disability. Reading disability is characterized by “reading achievement…that falls substantially below that expected given the individual’s chronological age, measured intelligence, and age-appropriate education” ( DSM-IV-TR, p.51).

#Lost twins achievements manual

Further, reading disability (or “Reading Disorder”, American Psychiatric Association, Diagnostic and Statistical Manual of Mental Disorders IV-TR, 2000) is not rare, affecting around 4% of school-age children in the U.S. Yet, individuals vary with respect to their level of reading ability. Reading is without question an important academic skill.