Exploring how nature and nurture affect the development of reading: An analysis of the Florida
Twin Project on Reading
Sara A. Hart1,2
Jessica A.R. Logan3
Brooke Soden-Hensler3
Sarah Kershaw2
Jeanette Taylor1
Christopher Schatschneider1,2
Supplemental Material
Additional Results
Cholesky decomposition
In addition to the biometric latent growth curve model, a Cholesky Decomposition was
also fit to the data (Supplemental Figure 1). This model does not represent a developmental
approach to examining the data, but does allow the decomposition of the variance on and
covariance among the grades of ORF scores into estimates of genetic (A), shared environmental
(C) and nonshared environmental (plus error; E) effects. In a Cholesky Decomposition, the first
set of biometric factors (A1, C1 and E1) represents the common genetic, shared environmental
and nonshared environmental influences among all the grades of ORF. The second set of
biometric factors (A2, C2 and E2) represents the genetic, shared environmental and nonshared
environmental influences among grades 2 to 5, after accounting for the first set of influences on
all of the grades. The third set (A3, C3 and E3) represents the covariance among grades 3 to 5,
after accounting for the first two sets of biometric factors. The fourth set (A4, C4 and E4)
represents the decomposition of the covariance between grades 4 and 5 after accounting for the
first three sets. Finally, the fifth set (A5, C5 and E5) represents the genetic, shared environmental
and nonshared environmental influences on grade 5 alone, after accounting for all the previous
influences.
Results from the Cholesky decomposition suggest that all of the pathways from the first
two genetic biometric factors are significant. This suggests that there are common genetic
influences underlying all of the grades of ORF scores (A1), and in addition to this common
variance there is a second source of genetic effects underlying grades 2 to 5 (A2). No other
genetic pathways were significant. Turning towards the shared environment biometric factors,
all pathways from C1 were significant, suggesting common shared environmental influences
underlying all five grades of ORF scores. Additionally, the first pathway from the C2 factor was
significant (pathway = .24). Finally, the results from the nonshared environmental biometric
factors suggest that there is a common environmental influence underlying grades 1 through 4
(E1 factor except for the pathway to grade 5, which is not significant). All other nonshared
environmental pathways are significant, except for the E4 pathway to grade 5 ORF.
Supplemental Table 1.
Path estimates from the Cholesky decomposition, representing the genetic (A), shared
environmental (C), and nonshared environmental (E) influences among the five grades of oral
reading fluency (ORF) scores [confidence intervals in brackets].
ORF grade 1
ORF grade 2
ORF grade 3
ORF grade 4
ORF grade 5
ORF grade 1
ORF grade 2
ORF grade 3
ORF grade 4
ORF grade 5
ORF grade 1
ORF grade 2
ORF grade 3
ORF grade 4
ORF grade 5
A1
.89* [.84-.94]
.67* [.60-.73]
.53* [.46-.60]
.43* [.32-.53]
.45* [.29-.61]
C1
.31* [.18-.42]
.39* [.22-.51]
.52* [.37-.62]
.48* [.31-.67]
.45* [.19-.34]
E1
.38* [.36-.41]
.18* [.14-.21]
.16* [.11-.20]
.18* [.07-.27]
.15 [.00-.32]
A2
A3
A4
A5
.45* [.39-.51]
.54* [.45-.62]
.60* [.45-.62]
.51* [.30-.76]
C2
.19 [.00-.31]
.02 [.00-.38]
.23 [.00-.50]
C3
.27 [.00-.36]
.36 [.00-.46]
C4
.00 [.00-.34]
C5
.24* [.07-.73]
.03 [.00-.60]
.10 [.00-.53]
.17 [.00-.61]
E2
.00 [.00-.26]
.00 [.00-.24]
.00 [.00-.37]
E3
.00 [.00-.16]
.00 [.00-.30]
E4
.00 [.00-.27]
E5
.34* [.32-.37]
.17* [.13-.21]
.15* [.08-.24]
.21* [.09-.32]
.32* [.30-.35]
.20* [.13-.26]
.24* [.14-.34]
.33* [.29-.38]
.09 [.00-.20]
.31* [.24-.37]
Note. * indicates significance as calculated through 95% confidence intervals which do not
bound zero.
Supplemental Figure 1. Cholesky Decomposition representing genetic (A), shared environmental (C) and nonshared environmental
(E) influences among grades 1 through 5 oral reading fluency (ORF) scores.
E1
C2
A2
E2
C3
A3
E3
C4
A4
E4
C5
A5
C1
A1
ORF g1
ORF g2
ORF g3
ORF g4
ORF g5
E5