C.Martel
23rd October 2019, 02:43 AM
The stability of educational achievement across school years is largely explained by genetic factors
Kaili Rimfeld, Margherita Malanchini, Eva Krapohl, Laurie J. Hannigan, Philip S. Dale & Robert Plomin
npj Science of Learning volume 3, Article number: 16 (2018) | Download Citation
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Abstract
Little is known about the etiology of developmental change and continuity in educational achievement. Here, we study achievement from primary school to the end of compulsory education for 6000 twin pairs in the UK-representative Twins Early Development Study sample. Results showed that educational achievement is highly heritable across school years and across subjects studied at school (twin heritability ~60%; SNP heritability ~30%); achievement is highly stable (phenotypic correlations ~0.70 from ages 7 to 16). Twin analyses, applying simplex and common pathway models, showed that genetic factors accounted for most of this stability (70%), even after controlling for intelligence (60%). Shared environmental factors also contributed to the stability, while change was mostly accounted for by individual-specific environmental factors. Polygenic scores, derived from a genome-wide association analysis of adult years of education, also showed stable effects on school achievement. We conclude that the remarkable stability of achievement is largely driven genetically even after accounting for intelligence.
Introduction
Educational achievement is important to society and to children as individuals. In fact, educational achievement has been shown to be a good predictor of many life outcomes, such as occupational status, happiness, health, and even life expectancy.1,2,3,4,5 Influences on educational achievement, including genetic and environmental etiologies, can best be studied during the period of compulsory education when the full range of family characteristics is represented. Compulsory education in the UK culminates with standardized nation-wide exams, the General Certificate of Secondary Education (GCSE). GCSE grades are a gateway to further education, university acceptance, and even later employment, shaping individuals’ life-long educational and professional trajectories. Previous twin research has shown that GCSE performance is highly heritable, and to a lesser extent explained by environmental factors.6 However, little is known about whether the same or different genetic and environmental effects contribute to individual differences in achievement over the course of compulsory education. In the present paper, quantitative (twin) and molecular genetic (DNA) methods are used to examine the etiology and developmental course of educational achievement during the primary and secondary education period, culminating in GCSE grades.
There is now converging evidence for the heritability of educational achievement across school years using family designs, such as twin and adoption studies, and DNA-based methods. Twin studies have shown that around 60% of individual differences in school achievement are explained by inherited differences in children’s DNA sequence.6,7,8,9,10,11,12,13,14,15,16 This holds when considering overall achievement scores as well as separate school subjects, from Sciences to Humanities.11,12 It is also possible to estimate heritability using DNA of unrelated individuals, where small DNA differences between individuals (single-nucleotide polymorphisms (SNPs)) are associated with the individuals’ scores in a trait of interest. Rather than estimating the association between each SNP and the trait, this method estimates the association between the trait and all the SNPs combined.17,18 This so-called SNP heritability for educational achievement has been shown to be around 20–30%.12,19,20,21 The SNP heritability is less than that estimated by twin studies partly because SNP heritability is limited to additive effects of common SNPs that are included in current arrays used to genotype SNPs. Because genome-wide association (GWA) studies have the same limitations as SNP heritability, SNP heritability is the current ceiling for the phenotypic variance that GWA studies can explain.
These univariate genetic analyses have shown that the heritability of educational achievement is substantial and consistent across school years, from primary to secondary education and culminating in the GCSEs.6,9 However, that conclusion is agnostic about the extent to which the same or different genetic factors contribute to individual differences in educational achievement longitudinally from age to age, that is, to stability and change. Understanding the developmental etiology of educational achievement in this way has considerable potential for illuminating the mechanisms that trigger differences in GCSE performance and, consequently, in educational and professional outcomes.
Multivariate genetic methods can be used to address this question of the etiology of age-to-age stability and change. Using a multivariate twin design we have previously demonstrated that, during the primary school years, genetic and shared environmental factors show substantial stability in English, Mathematics, and Science, while non-shared environmental factors contribute to change.9 However, the genetic and environmental etiology of stability and change of educational achievement across the longer span of school years, from primary school to secondary education and beyond, remains unexplored. Only a few longitudinal studies of reading ability have been reported. In one study, the stability of reading, measured as word recognition, was explained largely by genetic factors (around 70%) from primary through secondary school.22 Another study found that the etiology of reading fluency across the first five years of schooling, an important developmental time when students transition from ‘learning to read’ to ‘reading to learn’, was characterized by stable genetic and shared environmental influences.23 Two additional longitudinal analyses of reading comprehension in two different samples from the UK24 and US25 also showed substantial genetic stability. However, school achievement involves much more than reading.
To our knowledge, no longitudinal analysis has been conducted to assess the genetic and environmental etiology of continuity and change of educational achievement throughout compulsory education, for specific subjects as well as for general educational achievement. This is the purpose of the current study, which uses longitudinal data from age 7 to 16 on educational achievement from a UK-representative sample of 6000 twin pairs participating in the Twins Early Development Study (TEDS).26
We also addressed the issue of stability and change in school achievement, for the first time using DNA-based analyses. In addition to SNP heritability, which was described earlier, another recently developed method predicts academic achievement directly from DNA using specific SNPs that have been shown to be associated with the trait in GWA analyses. This method aggregates thousands of SNP associations, which individually have very small effects, into a genome-wide polygenic score (GPS)27 with effects weighted by results from the GWA discovery sample. A GPS can be used to predict variance in a trait for unrelated individuals in a sample independent of the GWA discovery sample. We will refer to this estimate as GPS heritability. It explains less variance than SNP heritability or twin study heritability because GPS heritability predicts educational achievement from specific SNPs.
Our EduYears GPS was derived from a GWA study of years of education for 300,000 individuals.28 We used the GWA summary data to create an EduYears GPS for each of 6000 unrelated individuals (one member of a twin pair) in our TEDS sample 26 in the UK. We correlated EduYears GPS with achievement measures at ages 7, 9, 12, and 16. We have previously shown that EduYears GPS predicts up to 9% of the variance in GCSE scores;29 here we extend this analysis and investigate results for specific subjects in addition to general achievement. The focus of our present analyses is the extent to which the EduYears GPS contributes to stability of educational achievement.
Genetic stability of school achievement might be explained fully or in part by general cognitive ability (g), which has also been shown to be substantially heritable10,30,31 and developmentally stable,32 and is one of the strongest predictors of school achievement.33,34,35,36 Moreover, the links between achievement and g have shown to be explained by genetic factors.7,33,37 Because g is a likely candidate to explain stability of school achievement across compulsory education, we also investigate the role of g in the stability of educational achievement, using both the twin design and DNA-based methods.
In summary, in this study we use twin analyses and GPS analyses of longitudinal data from TEDS from age 7 to age 16, including GCSE scores, to investigate three issues—the stability of general educational achievement, the stability of achievement in specific subjects, and the contribution of g to the stability of educational achievement.
https://www.nature.com/articles/s41539-018-0030-0
Your genes determine whether you are successful in skool. This explains why nig nogs are not successful in places of learning and why they have low IQs.
Kaili Rimfeld, Margherita Malanchini, Eva Krapohl, Laurie J. Hannigan, Philip S. Dale & Robert Plomin
npj Science of Learning volume 3, Article number: 16 (2018) | Download Citation
Article metrics
14k Accesses
1 Citations
249 Altmetric
Metrics details
Abstract
Little is known about the etiology of developmental change and continuity in educational achievement. Here, we study achievement from primary school to the end of compulsory education for 6000 twin pairs in the UK-representative Twins Early Development Study sample. Results showed that educational achievement is highly heritable across school years and across subjects studied at school (twin heritability ~60%; SNP heritability ~30%); achievement is highly stable (phenotypic correlations ~0.70 from ages 7 to 16). Twin analyses, applying simplex and common pathway models, showed that genetic factors accounted for most of this stability (70%), even after controlling for intelligence (60%). Shared environmental factors also contributed to the stability, while change was mostly accounted for by individual-specific environmental factors. Polygenic scores, derived from a genome-wide association analysis of adult years of education, also showed stable effects on school achievement. We conclude that the remarkable stability of achievement is largely driven genetically even after accounting for intelligence.
Introduction
Educational achievement is important to society and to children as individuals. In fact, educational achievement has been shown to be a good predictor of many life outcomes, such as occupational status, happiness, health, and even life expectancy.1,2,3,4,5 Influences on educational achievement, including genetic and environmental etiologies, can best be studied during the period of compulsory education when the full range of family characteristics is represented. Compulsory education in the UK culminates with standardized nation-wide exams, the General Certificate of Secondary Education (GCSE). GCSE grades are a gateway to further education, university acceptance, and even later employment, shaping individuals’ life-long educational and professional trajectories. Previous twin research has shown that GCSE performance is highly heritable, and to a lesser extent explained by environmental factors.6 However, little is known about whether the same or different genetic and environmental effects contribute to individual differences in achievement over the course of compulsory education. In the present paper, quantitative (twin) and molecular genetic (DNA) methods are used to examine the etiology and developmental course of educational achievement during the primary and secondary education period, culminating in GCSE grades.
There is now converging evidence for the heritability of educational achievement across school years using family designs, such as twin and adoption studies, and DNA-based methods. Twin studies have shown that around 60% of individual differences in school achievement are explained by inherited differences in children’s DNA sequence.6,7,8,9,10,11,12,13,14,15,16 This holds when considering overall achievement scores as well as separate school subjects, from Sciences to Humanities.11,12 It is also possible to estimate heritability using DNA of unrelated individuals, where small DNA differences between individuals (single-nucleotide polymorphisms (SNPs)) are associated with the individuals’ scores in a trait of interest. Rather than estimating the association between each SNP and the trait, this method estimates the association between the trait and all the SNPs combined.17,18 This so-called SNP heritability for educational achievement has been shown to be around 20–30%.12,19,20,21 The SNP heritability is less than that estimated by twin studies partly because SNP heritability is limited to additive effects of common SNPs that are included in current arrays used to genotype SNPs. Because genome-wide association (GWA) studies have the same limitations as SNP heritability, SNP heritability is the current ceiling for the phenotypic variance that GWA studies can explain.
These univariate genetic analyses have shown that the heritability of educational achievement is substantial and consistent across school years, from primary to secondary education and culminating in the GCSEs.6,9 However, that conclusion is agnostic about the extent to which the same or different genetic factors contribute to individual differences in educational achievement longitudinally from age to age, that is, to stability and change. Understanding the developmental etiology of educational achievement in this way has considerable potential for illuminating the mechanisms that trigger differences in GCSE performance and, consequently, in educational and professional outcomes.
Multivariate genetic methods can be used to address this question of the etiology of age-to-age stability and change. Using a multivariate twin design we have previously demonstrated that, during the primary school years, genetic and shared environmental factors show substantial stability in English, Mathematics, and Science, while non-shared environmental factors contribute to change.9 However, the genetic and environmental etiology of stability and change of educational achievement across the longer span of school years, from primary school to secondary education and beyond, remains unexplored. Only a few longitudinal studies of reading ability have been reported. In one study, the stability of reading, measured as word recognition, was explained largely by genetic factors (around 70%) from primary through secondary school.22 Another study found that the etiology of reading fluency across the first five years of schooling, an important developmental time when students transition from ‘learning to read’ to ‘reading to learn’, was characterized by stable genetic and shared environmental influences.23 Two additional longitudinal analyses of reading comprehension in two different samples from the UK24 and US25 also showed substantial genetic stability. However, school achievement involves much more than reading.
To our knowledge, no longitudinal analysis has been conducted to assess the genetic and environmental etiology of continuity and change of educational achievement throughout compulsory education, for specific subjects as well as for general educational achievement. This is the purpose of the current study, which uses longitudinal data from age 7 to 16 on educational achievement from a UK-representative sample of 6000 twin pairs participating in the Twins Early Development Study (TEDS).26
We also addressed the issue of stability and change in school achievement, for the first time using DNA-based analyses. In addition to SNP heritability, which was described earlier, another recently developed method predicts academic achievement directly from DNA using specific SNPs that have been shown to be associated with the trait in GWA analyses. This method aggregates thousands of SNP associations, which individually have very small effects, into a genome-wide polygenic score (GPS)27 with effects weighted by results from the GWA discovery sample. A GPS can be used to predict variance in a trait for unrelated individuals in a sample independent of the GWA discovery sample. We will refer to this estimate as GPS heritability. It explains less variance than SNP heritability or twin study heritability because GPS heritability predicts educational achievement from specific SNPs.
Our EduYears GPS was derived from a GWA study of years of education for 300,000 individuals.28 We used the GWA summary data to create an EduYears GPS for each of 6000 unrelated individuals (one member of a twin pair) in our TEDS sample 26 in the UK. We correlated EduYears GPS with achievement measures at ages 7, 9, 12, and 16. We have previously shown that EduYears GPS predicts up to 9% of the variance in GCSE scores;29 here we extend this analysis and investigate results for specific subjects in addition to general achievement. The focus of our present analyses is the extent to which the EduYears GPS contributes to stability of educational achievement.
Genetic stability of school achievement might be explained fully or in part by general cognitive ability (g), which has also been shown to be substantially heritable10,30,31 and developmentally stable,32 and is one of the strongest predictors of school achievement.33,34,35,36 Moreover, the links between achievement and g have shown to be explained by genetic factors.7,33,37 Because g is a likely candidate to explain stability of school achievement across compulsory education, we also investigate the role of g in the stability of educational achievement, using both the twin design and DNA-based methods.
In summary, in this study we use twin analyses and GPS analyses of longitudinal data from TEDS from age 7 to age 16, including GCSE scores, to investigate three issues—the stability of general educational achievement, the stability of achievement in specific subjects, and the contribution of g to the stability of educational achievement.
https://www.nature.com/articles/s41539-018-0030-0
Your genes determine whether you are successful in skool. This explains why nig nogs are not successful in places of learning and why they have low IQs.