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