Prevalence and clinical characteristics of dyslexia in primary school students.
BACKGROUND
Dyslexia is the most common subtype of learning disabilities with a prevalence ranging from 5-10 per cent. The central difficulty in dyslexia is the phonological awareness deficit. The authors have developed a screening test to assess the reading ability of Thai primary school students.


OBJECTIVE
1. To study the prevalence of dyslexia in first to sixth grade students at Wat Samiannaree School. 2. To study the clinical characteristics such as sex, neurological signs, verbal intelligence and comorbid attention deficit hyperactive disorder (ADHD) of the dyslexia group.


METHODS
A total of 486 first to sixth grade students were administered "Raven's progressive matrices test" for estimation of intellectual functioning. Those who scored below the fifth percentile were labeled as mental retardation and excluded from the study. The students' reading ability was evaluated by 3 steps; first by classroom teachers using some items of the screening test, second by the researchers examining some more items individually, and third by the special educator assessing more details in reading and phonology. The students who had a reading ability two-grade levels below their actual grades and impairment in phonology were diagnosed with dyslexia.


RESULTS
The prevalence of dyslexia and probable dyslexia were found to be 6.3 per cent and 12.6 per cent, respectively. The male to female ratio of dyslexia was 3.4:1. The dyslexia group had significantly lower Thai language scores than those of the normal group (p < 0.05). All of the dyslexia group had a normal grossly neurological examination but 90 per cent showed positive soft neurological signs. Mean verbal intellectual quotient score in the dyslexia group assessed by using Wechsler Intelligence Scales for Children--Revised was 76 +/- 7. The comorbid ADHD was 8.7 per cent in the dyslexia group.


CONCLUSIONS
Dyslexia was a common problem among primary school students in this study. Further studies in a larger population and different socioeconomic statuses are required to determine the prevalence of dyslexia in the general population. The authors suggest evaluating the reading ability carefully by using a test that can detect phonological awareness deficit in all children who have learning problems.
Roongpraiwan
Rawiwan
R
Department of Pediatrics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand.
Ruangdaraganon
Nichara
N
Visudhiphan
Pongsak
P
Santikul
Kanitta
K
D002648:Child; D004410:Dyslexia / Q000150:complications / Q000175:diagnosis* / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D015995:Prevalence; D012574:Schools / Q000706:statistics & numerical data*; D013785:Thailand / Q000453:epidemiology