Increasing SLI – AN international myth or a fact?
Kaisa
Launonen, professor, speech and language therapist. Department of Speech
Sciences,
INTRODUCTION
The discussion on increasing numbers of
children’s specific language impairments (SLI) has been active, both
internationally and in
The great majority of internationally reported
research on children’s language development and its disorders has been done in
English and on English-speaking children, but during the latest decades
researchers have reported studies on children with language disorders, speaking
also other languages, for example German (Clahsen 1992), Swedish (Hansson &
Nettelbladt 1995), Italian (Leonard, Bortolini, Caselli, MacGregor &
Sabbadini 1992), Hebrew (Dromi, Leonard & Shteiman1993), Swedish-Arabic
(Salameh 2003) and Dutch (van Daal, Verhoeven, & van Balkom, 2004). Even if
languages share some universal features, they also seem to have language
specific features (e.g. Bortolini et al. 2002). This fact accentuates the need
for studies on language development made in different language areas. At the
same time, comparative studies should be made between languages, in order to
make comparisons and generalising conclusions possible.
The prevalence of specific language impairment
or delay in up to 7 year old children, reported in different studies, varies
from 0,6% to 33,6 % (Law et al. 1998). There are large methodological
differences between studies, which complicate their comparison, for example:
the way language impairments are identified, whether speech and language delay
are looked at together or separately, what the population is from which the
data has been collected, and what the definition criteria of the impairment
are. The number of potential cases of primary speech and language delay is
high, with a median figure of 5,95% reported for delays in either speech or
language. According to Law and associates (1998), there is no evidence to
suggest that there is a real increase in cases in the period covered by review
1967 - 1997. According to the authors, this suggests that the estimation of
prevalence and the demands made on services are not necessarily equivalent.
Language, its development and developmental
impairments are studied in many disciplines, which also define language each
from their own point of view. Terms and diagnoses do, however, make a
difference, because many services in a society, the accessibility of
intervention, as well as the choice of school form may partly be based on
diagnosis, as is the case in
METHOD
The data of this study was collected in the
third biggest city in
In this retrospective study, the prevalence of
SLI was examined in the primary health care system of the city described above,
through eleven years, 1989 – 1999. SLI
was defined by the ICD-9 diagnoses 3153A and 3153X and the ICD-10 diagnoses
F80.1 and F80.2. Also the diagnosis SLI without diagnosis number was included.
The samples of delayed language development were from years 1989-1991 and
1996-1998. The data was collected from the statistics of the speech and
language therapists of the city. Every year the speech and language therapists
compiled statistics on their patients, e.g. amount, diagnoses and ages. One
child is included in the statistics every year s/he has used the speech and
language therapy services. Therefore, it is possible to examine the prevalence
but not the incidence of SLI.
The speech and language therapists' statistics
were collected into SPSS for Windows. The data were processed with different
statistical tests, which showed a statistically significant rise (p<0,001).
0-hypothesis was that there were no differences in the prevalence of SLI
between the years or during the whole period of this study. The whole data was
N=2480.
RESEARCH
QUESTIONS
In this presentation we will look at
a. the prevalence of SLI,
b. the prevalence of delayed language
development in two samples and
c. the numbers of children with SLI and speech
and language therapists.
RESULTS
PREVALENCE OF SLI
In this data, there were 1455 findings of SLI.
In the age group up to 15 years, the prevalence of SLI increased from 0,04% to
0,7%. In the age group under 6 years the prevalence increased from 0,09% to
0,9% (table 1). The increase during this period was statistically
significant.
TABLE 1. Years 1989 - 1999:
population, the number of the children up to 15 years of age, the number of SLI
diagnosis and the prevalence % of SLI. The lowest three lines show the
prevalence up to 6 years of age.
|
Year |
1989 |
1990 |
1991 |
1992 |
1993 |
1994 |
1995 |
1996 |
1997 |
1998 |
1999 |
|
|
population of the city |
152 272 |
154893 |
157276 |
159228 |
161133 |
164376 |
166480 |
168778 |
171297 |
173860 |
176386 |
|
|
age 0-15 years |
34 040 |
34 289 |
34 775 |
35 228 |
35 792 |
36 817 |
37 283 |
37 696 |
38 232 |
38 295 |
38 344 |
|
|
Dg (n) age 0 – 15 years |
15 |
12 |
33 |
60 |
108 |
134 |
163 |
220 |
232 |
212 |
266 |
|
|
SLI% age 0 – 15 years |
0,04 |
0,03 |
0,09 |
0,17 |
0,31 |
0,36 |
0,44 |
0,58 |
0,61 |
0,55 |
0,69 |
|
|
age 0-6 years |
15 329 |
15452 |
15957 |
16418 |
16882 |
17685 |
17939 |
18 025 |
17 974 |
17 669 |
17 381 |
|
|
Dg (n) age 0 - 6 |
14 |
12 |
23 |
39 |
77 |
100 |
119 |
160 |
163 |
130 |
147 |
|
|
SLI% age 0 – 6 years |
0,09 |
0,08 |
0,14 |
0,23 |
0,45 |
0,56 |
0,66 |
0,89 |
0,91 |
0,73 |
0,85 |
|
Prevalence of delayed language development (DLD) in two samples
Two samples of delayed language development
(DLD) were collected. The first sample of three years was from years 1989 to
1991 and the second sample from 1996 to 1998. DLD does not have as precise a
definition as SLI. A physician or a speech and language therapist may define
the child's language difficulty as delayed language development. The number of
children with DLD increased statistically significantly during the years of the
two samples. The increase of DLD was, however, lower than the increase of SLI
(table 2).
TABLE 2. Two samples of DLD and SLI.
|
Sample
years |
DLD |
SLI in
age group 0 – 15 years |
|
1989-1991 |
116 |
60 |
|
1996-1998 |
909 |
664 |
|
Ratio between years |
7,8 |
11,0 |
In speech and language therapists´ statistics,
delayed language development (DLD) is used only until 6 years of age. For this
reason, table 3 shows the numbers of children with SLI under school age only.
When putting together the numbers of SLI and DLD in three years (one sample)
and the population and divide it with three we get the mean prevalence for one
year (table 3).
TABLE 3. Two
samples, the mean numbers of 0 – 6 years old children, DLD and SLI and mean
prevalence.
|
Years of sample |
0 – 6 v |
DLD |
SLI |
prevalence |
|
1989 – 1991 |
15 579 |
38 |
16 |
0,3% |
|
1996 - 1998 |
17 889 |
303 |
151 |
2,5% |
NUMBERS OF Children with SLI and speech and language therapists
In the first year of this study (1989), there
were nine speech and language therapists and 15 children with SLI in the city
of this study. The mean number of children with SLI which one therapist had
examined or given therapy to in this year was 1,6. In 1999 the mean number was
11,1. (table 4).
TABLE 4. The
numbers of speech and language therapists and children with SLI and their ratio
1989 - 1999.
|
Year |
89 |
90 |
91 |
92 |
93 |
94 |
95 |
96 |
97 |
98 |
99 |
|
Children with SLI |
15 |
12 |
33 |
60 |
108 |
134 |
163 |
220 |
232 |
212 |
266 |
|
Speech and
language therapists |
9 |
9 |
9 |
9 |
21 |
21 |
21 |
21 |
22 |
24 |
24 |
|
SLI/ Therapists |
1,6 |
1,3 |
3,7 |
6,7 |
5,1 |
6,4 |
7,8 |
10,5 |
10,5 |
8,8 |
11,1 |
DISCUSSION
During the follow-up period of this study the
prevalence of SLI increased, but it still remained under one percent in both
age groups. Because SLI is considered to have a stability of language
impairment profiles, the data of this study was collected up to 15 years. The
prevalence of SLI in this group was 0,7%. In age group up to six years, the
prevalence of SLI was 0,9%. In this study, the prevalence of SLI follows the
lowest estimates in the international studies. The explanation may be that only
the most serious speech and language impairments were included in the SLI cases
of this study. Even though the prevalence numbers are low, it does not
necessarily mean under-diagnosing. The health care system of the city in this
study is considered to be well functioning and has shown its comprehensiveness
by clinical experience.
There have been some speculations that SLI
would be a trend-diagnosis or that the diagnosis is moving from one group to
another. In this study, this movement could have been only from the delayed
language development group to the SLI group. However, also the prevalence of
DLD increased in this study. The statistically significant increase was seen
both in the DLD and in the SLI group. When the numbers of SLI and DLD are
counted together, this study shows a prevalence of 2,5% in the age group up to
six years. This prevalence number comes closer to the international median
figures (Law et al. 1998) than do the pure SLI numbers in this study.
In the beginning of the follow-up period of
this study, each speech and language therapist had only one or two children
with SLI in therapy during one year, but in the latter part of the period the
number was ten times bigger. In the beginning of the follow-up period,
therapists had good resources to take care of therapy needs, while to the end
of this period they had to develop more ecological ways to support their
clients speech and language development.
CONCLUSION
Disorders in children's language development
form the biggest group of disorders in speech and language therapists´ daily
work in primary health care. The prevalence numbers of SLI in this study
correspond the smallest numbers in internationally reported studies. Still the
results suggest that the prevalence of SLI increased significantly in the
decade of the 1990’s. This phenomenon was obvious also in clinical work, and it
has forced — or at least challenged – the speech and language therapists to
develop their therapy towards more ecological intervention practices.
It seems that in this city intervention is
functioning well in younger ages of children with SLI. In this decade, the
children with SLI who were born in the beginning of the 90´s, will be finishing
their elementary school, and the school system has a challenging job to find
vocational education for them. Our society has a big challenge in recreating
education and occupations also with less academic demands. This task is
especially challenging because the values in our society, as well as those in
many other Western countries, emphasize – even overemphasize - language skills.
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