Table 2.

Article coding key

Category	Value Description
Publication Type	1 = peer reviewed journal article
	2 = thesis or dissertation
	3 = unpublished data
Study Type	1 = twins
	2 = twins and siblings
	3 = twins and adoption
	4 = nontwins and parents
	5 = family design
Twin Project	1 = FTP
	2 = TEDS (E-risk)
	3 = CLDRC
	4 = WRRMP
	5 = ILTS
	6 = MISTRA
	7 = NLSY
	8 = Other
	9 = LTS
	10 = NTR
	11 = ATP
	12 = QTS
Clinical Status	0 = 75% or more typically-developing
	1 = 75% or more had reading disability
	2 = 75% or more had math disability
	3 = mix of typically-developing students and students with a learning disability
	4 = 75% or more comorbid reading and math disability
	5 = Other
Race (Reported/Inferred)	0 = 75% or more Caucasian
	1 = 75% or more Black/African American
	2 = 75% or more Hispanic
	3 = 75% or more Asian
	4 = Other
	5 = Mixed (more than one race)
	6 = Not Reported
Nationality	1 = USA
	2 = Australian
	3 = Scandinavian
	4 = UK
	5 = More than one nationality
	6 = Canadian
	7 = Dutch
	8 = Other
	9 = Not Applicable
Grade-Level	0 = Preschool/Kindergarten
	1 = 1^st grade
	2 = 2^nd grade
	3 = 3^rd grade
	4 = 4^th grade
	5 = 5^th grade
	6 = 6^th grade
	7 = 7^th grade
	8 = 8^th grade
	9 = 9^th grade
	10 = 10^th grade
	11 = 11^th grade
	12 = 12^th grade
	13 = Mixed elementary
	14 = Mixed middle school
	15 = Mixed high school
	16 = Undergraduates
	17 = Not Applicable
ADHD Assessment	1 = DBRS
	2 = DICA
	3 = Revised Conner’s
	4 = DCB
	5 = SWAN
	6 = Other
	7 = ATBRS
	8 = DBD
	9 = ADHD composite (more than one ADHD assessment)
	10 = Not Applicable
	11 = CBCL
	12 = SBQ
Reading Assessment	1 = PIAT reading subtest
	2 = WJ-Reading subtest
	3 = Reading Composite (more than one reading assessment)
	4 = Netherlands PMS reading subtest
	5 = UKNC reading subtest
	6 = Other
	7 = FCAT reading subtest
	8 = FAIR
	9 = GOAL reading subtest
	10 = TOWRE
	11 = Alouette-R reading subtest
	12 = WIAT reading subtest
	14 = Reading Difficulties Questionnaire
	15 = CTOPP RAN
	16 = NAPLAN
	17 = OCT
	18 = THAL
Reading Domain	1 = Reading Comprehension
	2 = Reading Fluency
	3 = Spelling (includes Orthographic Choice, Print Knowledge)
	4 = Phonological Awareness
	5 = Decoding
	6 = Other (includes Vocab, Grammar, Syntax, RAN)
	7 = Multiple (more than one reading domain)
	8 = Not Applicable
	9 = Difficulties with Reading
Reading Assessment Format	1 = Cloze/Short Answer
	2 = Multiple Choice
	3 = Mixed (more than one format)
	4 = Rating Scale
	5 = Retell (includes spoken/oral response)
	6 = Timed
	7 = True/False
	8 = Other
	9 = Not Applicable
Math Assessment	1 = PIAT math subtest
	2 = WJ-Math subtest
	3 = Netherlands PMS math subtest
	4 = Math Composite (more than one math assessment)
	5 = UKNC math subtest
	6 = Other
	7 = GOAL math subtest
	8 = MAT math subtest
	9 = WIAT math subtest
	10 = Not Applicable
	11 = NFER 5–14 Mathematics Series
	12 = NAPLAN
Math Domain	1 = Math fluency
	2 = Calculation
	3 = Spatial Ability
	4 = Problem Solving
	5 = Quantitative Concepts (includes Numeracy, Number Line, Dots Task)
	6 = Other
	7 = Multiple (more than one math domain)
	8 = Not Applicable
	9 = Math Difficulties
Math Assessment Format	1 = Cloze/Short Answer
	2 = Multiple Choice
	3 = Mixed (more than one format)
	4 = Rating Scale
	5 = Timed
	6 = True/False
	7 = Other
	8 = Not Applicable
	9 = Parent-Report
	10 = Teacher-Report
DeFries-Fulker Method	1 = Yes
	2 = No
ADHD Component	1 = Overall ADHD
	2 = Hyperactivity/Impulsivity
	3 = Inattention
	4 = Not Applicable

Note. For Reading Assessment, the value “13” was unintentionally skipped in the coding scheme used.