Post on 13-Jan-2015
description
How common is specific language impairment
(SLI)?
Dorothy V M Bishop
Our best estimate of frequency of SLI= 3%
• This corresponds to around
One child in every classroom
• But the number is not set in stone and will vary from place to place and according to definition
• So you may hear very different numbers reported • Here we’ll present some of the evidence behind the numbers
SLI is identified when
• Child’s language ability is well below age level
• Language problems aren’t explained in terms of known causes such as hearing loss, autism, general intellectual retardation
• Language problems interfere with everyday life at home and /or school
Numbers with SLI will depend on precise definition
• Child’s language ability is well below age level
• Not explained by other factors
All these terms can be interpreted in different ways
Study conducted in Mannheim, Germany
• 320 children after excluding those with hearing loss or autism
• N.B. Selected to represent range of levels of biological and environmental risk
• Seen at 4.5 yr and 8 yr for assessments of expressive and receptive language* and nonverbal ability
*One expressive, one receptive subtest from Illinois Test of Psycholinguistic abilities
Weindrich, D., Jennen-Steinmetz, C., Laucht, M., Esser, G., & Schmidt, M. H. (2000). Epidemiology and prognosis of specific disorders of language and scholastic skills. European Child and Adolescent Psychiatry, 9(3), 186-194.
Strict definition of SLI
Criteria of International Classification of Diseases,
ICD-10
a)Performance on language test 2 SD or more below group mean (i.e. in bottom 3%)
b)Language score at least 1 SD below nonverbal IQ score
c)Nonverbal IQ at least 70
Strict definition of SLI
ICD-10 criterion
a)Performance on language test 2 SD or more below group mean (i.e. in bottom 3%)
b)Language score at least 1 SD below nonverbal IQ score
c)Nonverbal IQ at least 70
Criterion met by •7 children (2.2%) at 4.5 yr •3 children (1%) at 8 yr
Clinical definition of SLI
ICD-10 criterion widely viewed as arbitrary and not mapping on to clinical need
Therefore developed a clinical definition that relaxed the severity of language impairment required
a)Performance on language test 1.5 SD or more below group mean (i.e. in bottom 7%)
Other ICD10 criteria were retained
Clinical definition of SLI
a) Performance on language test 1.5 SD or more below group mean (i.e. in bottom 7%)
b) Language score at least 1 SD below nonverbal IQ score
c) Nonverbal IQ at least 70
Criterion met by •14 children (4.3%) at 4.5 yr •11 children (3.4%) at 8 yr
(N.B. includes those meeting ICD10 criteria)
Least strict definition of SLI
Nonspecific language impairment
Remove need for mismatch between language and IQ. Child just has to show:a)Performance on language test 1.5 SD or more below group mean (i.e. in bottom 7%)
b)Nonverbal IQ at least 70
Criterion met by •21 children (6.6%) at 4.5 yr •11 children (3.4%) at 8 yr
(N.B. includes those meeting ICD10 and clinical criteria)
More children included as criteria become less stringent
Strict ICD10
Clinical
NonspecificLanguage Impairment
Frequency of SLI will also vary from population to population
• Most studies find more common in boys than girls (though will depend on definition)
• In some children problems resolve with age, so fewer older children meet criteria for SLI
• Mannheim study found SLI more common when there was either biological risk (low birth weight and/or preterm birth) or psychosocial risk (range of family factors, including parental age, education, income, etc).
A complication: Speech problems
• Many studies combine speech and language problems into a single category
• Speech problems involve difficulties articulating all the sounds of the language and are quite common in preschool children
• Speech problems can co-occur with language problems, but often they occur in isolation
• Speech problems are a common reason for a young child to be referred for speech and language therapy
Some other relevant studies
• Stevenson & Richman (1976) 3 yr olds in UK; delayed language development in 3.1%, but most with low nonverbal ability; Specific language delay in only 0.57%
• Beitchman et al (1986), 5-year-olds in Ottawa; 12.5% had language problems (No nonverbal assessment)
• Tomblin et al (1997) 6-year-olds in US mid-West; 7.4% had SLI (but only 29% had been identified as in need of services)
Impact of language impairment on everyday life
• Most studies that estimate frequency of SLI have relied just on language test scores
• Ideally should also consider impact on child’s everyday life at home and school
• Language tests may miss key aspects of communication problems (especially if only a short test battery is used)
• But also, some children with low language test scores may actually function well at home and school
• Parent or teacher report should supplement tests to give a fuller picture
Study using parent/teacher report
• Longitudinal Australian Cohort Study: representative sample of 4983 children aged 4 to 5 years
• 25% parents concerned about how child talked and made speech sounds (but this includes articulation)
• 9% parents concerned about language understanding• Teacher concern about expressive language in 22% and
concern about comprehension in 17%• But N.B. parent concern only weakly related to language test
scores• 10% accessed a speech-language therapist over past 12 mo
McLeod, S., & Harrison, L. J. (2009). Epidemiology of speech and language impairment in a nationally representative sample of 4-to 5-year-old children. Journal of Speech, Language, and Hearing Research, 52(5), 1213-1229.
Best estimate of frequency of SLI= 3%
• But overall, general convergence from studies that this is reasonable estimate of proportion of children with language problems severe enough to affect their social interaction with others and/or their success at school, and which have no known cause
• RALLI exists because we think that many people aren’t aware of SLI, even though it is a common childhood condition that has real effects on children’s lives
• PLEASE HELP SPREAD THE WORD BY PUBLICISING OUR CHANNEL: http://www.youtube.com/RALLIcampaign/
For references related to this talk please see
http://www.slideshare.net/RALLICampaign/how-common-is-sli
and
http://www.slideshare.net/RALLICampaign/how-is-specific-language-impairment-identified-13957123