Table 3.

Model fit statistics for phenotypic confirmatory factor analysis (best-fitting model in boldface).

Model	−2LL	df	AIC	BIC
Model 1	4796.38	2055	686.38	94.04
1 factor
Model 2	4646.57	2054	538.57	20.26
2 factors [Reading + Math]
Model 3	4618.36	2052	514.36	8.39
3 factors[Word Recognition + Comprehension + Math (Math Fluency)]
Model 4	4587.80	2049	489.80	−3.52
4 factors[Decoding + Fluency (math Fluency) + Comprehension + Math]
Model 5	4567.40	2049	469.40	−13.72
4 factors[Decoding + Fluency + Comprehension + Math (math Fluency)]

Note. Only one child from the twin pair was used for these analyses. AIC=Akaike Information Criterion. BIC=sample-size adjusted Bayesian Information Criterion Model 1 contains one factor, representing all available measures grouped as a domain general factor. Model 2 contains two factors, representing a Reading (WRMT Word Attack, Word Identification and Passage Comprehension, PIAT Reading Comprehension, the DIBELS and the TOWRE) and Math (WJ Applied Problems, Quantitative Concepts, Calculation and math Fluency).Model 3 represents three factors, incorporating Word Recognition (WRMT Word Attack and Word Identification, the DIBELS and the TOWRE), Comprehension(WRMT Passage Comprehension and PIAT Reading Comprehension) and finally all Math measures (WJ Applied Problems, Quantitative Concepts, Calculation and math Fluency). Model 4 contains four factors, Decoding (WRMT Word Attack, Word Identification), Fluency (the DIBELS, the TOWRE and WJ math Fluency), Comprehension (WRMT Passage Comprehension and PIAT Reading Comprehension), and Math (WJ Applied Problems, Quantitative Concepts and Calculation). Finally, Model 5 also contain four factors, Decoding (WRMT Word Attack, Word Identification), Fluency (the DIBELS and the TOWRE), Comprehension (WRMT Passage Comprehension and PIAT Reading Comprehension), and Math (WJ Applied Problems, Quantitative Concepts, Calculation and math Fluency).