Middle childhood
Box 29.1
Definitions of specific language impairment (SLI)
SLI
is generally defined in terms of a discrepancy between non-verbal cognitive functioning
and language skills, as measured on standardized tests. Debate centres on the required size of
that disparity, the level of language impairment required, and the measurement of verbal and
non-verbal abilities. For example:
•
The
International Classification of Diseases, 10th revision
(
ICD-10) requires language
difficulties greater than 2 standard deviations (SD)
below
the mean, with verbal skills at
least 1 SD
below
measures of non-verbal cognitive functioning.
•
The
Diagnostic and Statistical Manual of Mental Disorders-IV-Text Revision
(DSM-IV-TR),
requires
substantially worse
performance on measures of verbal abilities compared to
non-verbal cognitive functioning. What constitutes ‘substantial’ is not defined operationally,
though
functional impairment
is required — i.e. SLI interferes with academic or
occupational achievement, or with social interaction.
•
The clinical research definition of SLI
[19] works with threshold and discrepancy measures
that enable consistent identification of SLI by speech and language therapists. It requires a
combination of language difficulties, assessed on a composite standardized language
measure, that fall 1.25 SD
below
the mean (approximately, the 10th centile). Plus,
adequate non-verbal cognitive functioning (i.e. a Performance IQ
greater
than 1 SD below
the mean, equating to a standard score of 85 or higher).
educational and public health resources. SLI is
a common disorder, estimated to affect approxi-
mately 6% of the population, with boys being more
affected than girls at a ratio of 2:1. Although SLI
is the term most commonly used in research, it is
worth noting that it is rarely used in clinical set-
tings, where the condition is more likely to present
under a variety of other names. These can include:
‘language disorders’ subdivided into ‘expressive’
and ‘mixed expressive-receptive’ types [
Diagnostic
and Statistical Manual of Mental Disorders, Fourth
Edition – Text Revision
(DSM-IV-TR) and pro-
posed DSM-5]; ‘speech, language and commu-
nication needs’ (Royal College of Speech and
Language Therapists); ‘developmental language
delay’, ‘language impairment’, ‘primary language
difficulties’ and other similar names (educational
practice settings).
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