Sex differences in developmental reading disability: new findings from 4 epidemiological studies.
BACKGROUND
An influential article published in 1990 claimed that the increased rate of reading disability in boys was a consequence of referral bias.


OBJECTIVE
To summarize the history of research on sex differences in reading disability and to provide new evidence from 4 independent epidemiological studies about the nature, extent, and significance of sex differences in reading disability.


METHODS
The Dunedin Multidisciplinary Health and Development Study comprised 989 individuals (52.1% male) in a cohort born between April 1972 and March 1973 in Dunedin, New Zealand, and followed up from age 3 years; reading performance and IQ were assessed at ages 7, 9, and 11 years using the Burt Word Reading Test and the Wechsler Intelligence Scale for Children-Revised (WISC-R), respectively. The Christchurch Health and Development Study comprised 895 individuals (50% male) in a prospectively studied cohort born in the Christchurch, New Zealand, region during a 4-month period in 1977; reading performance and IQ were assessed at ages 8 to 10 years using the Burt Word Reading Test and the WISC-R. The Office for National Statistics (ONS) Study comprised a UK nationally representative sample of 5752 children (50.1% male) aged 9 to 15 years in 1999; reading was assessed on the British Ability Scales II and IQ on the British Picture Vocabulary Scales II. The Environmental Risk Longitudinal Twin Study (E-Risk) comprised 2163 twin children from England and Wales (49.1% male) identified at birth in 1994 and 1995 and included administration of the Test of Word Reading Efficiency at age 7 years and the Wechsler Preschool and Primary Scale of Intelligence-Revised as a test of IQ at age 5 years.


METHODS
Reading performance by sex in the lowest 15% of the distribution for all 4 studies, with and without taking IQ into account.


RESULTS
In all 4 studies, the rates of reading disability were significantly higher in boys. For non-IQ-referenced reading disability: Dunedin study, 21.6% in boys vs 7.9% in girls (odds ratio [OR], 3.19; 95% confidence interval [CI], 2.15-4.17); Christchurch study, 20.6% in boys vs 9.8% in girls (OR, 2.38; 95% CI, 1.62-3.50); ONS study, 17.6% in boys vs 13.0% in girls (OR, 1.43; 95% CI, 1.23-1.65); and E-Risk, 18.0% in boys vs 13.0% in girls (OR, 1.39; 95% CI, 1.04-1.86). The rates for IQ-referenced reading disabilities were similar.


CONCLUSIONS
Reading disabilities are clearly more frequent in boys than in girls.
Rutter
Michael
M
Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, King's College, Denmark Hill, London, England. j.wickham@iop.kcl.ac.uk
Caspi
Avshalom
A
Fergusson
David
D
Horwood
L John
LJ
Goodman
Robert
R
Maughan
Barbara
B
Moffitt
Terrie E
TE
Meltzer
Howard
H
Carroll
Julia
J
D001077:Aptitude Tests; D002648:Child; D004410:Dyslexia / Q000453:epidemiology*; D016021:Epidemiologic Studies; D005260:Female; D006801:Humans; D008297:Male; D012737:Sex Factors; D018433:Twin Studies as Topic