The document discusses the prevalence of specific language impairment (SLI) in children. [1] Most studies estimate that SLI affects around 3% of children, meaning approximately one child in every classroom. [2] However, the exact number varies depending on the definition used to identify SLI and can range from 1% to 7% depending on how strict the criteria is. [3] SLI is most common when using broader definitions that do not require as severe language deficits or a discrepancy between language and nonverbal abilities.

1. How common is
specific language impairment
(SLI)?
Dorothy V M Bishop

2. 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

3. 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

4. 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

5. 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.

6. 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

7. 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

8. 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

9. 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)

10. 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)

11. More children included as
criteria become less stringent
Strict ICD10
Clinical
Nonspecific
Language
Impairment

12. 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).

13. 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

14. 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)

15. 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

16. 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.

17. 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/

18. 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