Context An influential article published in 1990 claimed that the increased
rate of reading disability in boys was a consequence of referral bias.
Objectives 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.
Design, Setting, and Participants 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.
Main Outcome Measure 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
Conclusion Reading disabilities are clearly more frequent in boys than in girls.