| Hein, Jakob : The Specific disorder of arithmetical skills. Prevalence study in an urban population sample and its clinico-neuropsychological validation. Including a data comparison with a rural population sample study. |
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As described in chapter 3.1.1., we examined an urban population sample in the present study. Preceding the present investigation, our study group had studied the prevalence of the Specific disorder of arithmetical skills in a rural population sample in 1995 Häußer, 1995 . The theoretical background and methodology were similar to those of the present study and are laid out in another publication by our group Rüdiger, 1994 . Therefore we attempted to compare the data of both studies.
Häußer carried out his study in the early fall of 1993 in the Dahme-Spreewald-district of the federal state of Brandenburg. Similar to the present study, laid out in chapter 3.1.2., the basic conception of Häußer for evaluating the prevalence was to assess the mathematics and language skills with standardized academic achievement tests. As defined in the ICD-10, an arithmetical performance significantly below the results of the language test led to the working diagnosis of a Specific disorder of arithmetical skills.
The study was conducted in eight third-grade-classes from August to September 1993, at the beginning of the academic year. The classes were chosen from four schools. A total of 181 probands underwent testing, 92 of which were boys and 89 girls. The Mathematics test for second grades (MT-2; Feller &Hugo, 1981 ) and the Diagnostic spelling test for second grades (DRT-2; Müller, 1983 ) were applied to the students, and their teachers were asked to evaluate their students performance in a questionnaire. The data were collected in an anonymous fashion.
An average or above-average performance is defined in the DRT-2 as a result above the 34th percentile of the standardization sample, and in the MT-2 as a performance above the 17th percentile of the standardization sample.
The results in MT-2 and DRT-2 corresponded very well with those of the standardization samples of the tests, assessed in 1981 and 1983, respectively. The average value in the MT-2 standardization sample was for example a score of 52.47. Häußer found in his sample an average score of 52.4 in the MT-2. In order to make a working diagnosis for a suspected Specific disorder of arithmetical skills, the author consequently used the criteria of the MT-2 and DRT-2 to define discrepancies between academic skills. The criteria are shown in Table 4:
Tab. 4. Criteria for a likely learning disorder of the rural population sample.
|
Class of Learning disorder |
Percentile MT-2 |
Percentile DRT-2 |
|
Specific disorder of arithmetical skills |
<17 |
>34 |
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|
Specific disorder of reading skills |
>17 |
<26 |
|
Combined learning disorder |
<17 |
<26 |
Twelve probands (6.6 %) met the criteria for a suspected Specific disorder of arithmetical skills. Of those nine (75 %) agreed to participate in a further clinical and neuropsychological validation process, which included a clinical and neurological examination, EEG, AEP, VEP and WISC-R-A as well as a test of hand-dominance. A Computer-assisted tomography (cCAT) of one proband and a common X-ray image of the skull of another proband were obtained. In the validation process only two of the probands were found to meet full diagnostic criteria for a Specific disorder of arithmetical skills of the ICD-10. Both of these probands showed left-sided functional deficits in the EEG and the clinical examination. In four probands the overall IQ was to low to fulfill the discrepancy criterion, and the arithmetical abilities of the remaining three probands were found to be within normal limits.
There are many differences but also important similarities between the two studies of our research group, the present investigation of a city population sample and the one of a rural population sample by Häußer.
We conducted our study of the city population sample in winter, towards the end of the third academic year, whereas Häußer made his in early fall at the beginning of the academic year. Consequently, the present study used standardized academic achievement tests for the end of the third grade, while in the rural population study those for the second grade were applied. Another major difference is the fact, that in the former study our results of the standardized academic achievement test were significantly below those of the standardization sample, while the latter found good correlation of the data with the standardization sample. Table 5 shows a comparison of both population samples, when the standardization criteria for the achievement tests (see Table 4) are applied.
Tab.5: Comparison of the frequency of suspected Learning disorders in a city vs. rural population sample if the standardization norms of the screening instruments would have been applied.
|
|
Frequency (%) |
|
|
Class of Learning disorder |
Rural population |
City population |
|
Specific disorder of arithmetical skills |
6.6 |
10.6 |
|
Specific disorder of reading skills |
12.7 |
12.3 |
|
Combined learning disorder |
3.3 |
48.6 |
|
No learning disorder |
77.3 |
28.5 |
Another dissimilarity constituted the fact that there were no probands with another language than German as their first language in the rural population sample, while
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there were 36 (19.6 %) such probands in the city population sample. However, such probands were underrepresented in the group of probands with a suspected Specific disorder of arithmetical skills.These important differences notwithstanding, there were also many similarities between the two investigations. Both studies were conducted with a practically equivalent number (n=181 vs. 182) of third-grade probands. No significant gender differences in academic achievement were found in either study and the results were homogeneously distributed. Most notably, in spite of different criteria and test instruments there was the same number of probands with a suspected Specific disorder of arithmetical skills, and the prevalence rates were practically identical in both studies (6.6 vs. 6.59 %).
While we detected abnormalities with cMRI, Häußer found no abnormality in the two imaging studies he obtained. Since it is well-known that the cMRI is superior to other imaging techniques for information about the neuronal structure of the brain, we would argue for the cMRI as the imaging technique of choice when evaluating a Specific disorder of arithmetical skills in the absence of a clinically suspected gross anatomical abnormality.
The most conspicuous difference between both studies is probably the average performance of the rural population sample in the standardized academic achievement test in comparison to the below-average results of the city population sample in those tests. A number of reasons is responsible for that circumstance.
On one hand, the difference between both population samples is not surprising and it seems unlikely that only 28.5 % of the probands of our city population sample do not have any form of a learning disorder. We applied the achievement test too early for reasons explained in chapter 3.1. It is therefore not unexpected that the test results were below the average of the standardization sample. Häußer, on the other hand, applied the MT-2 and the DRT-2 at the latest time permitted by the test criteria. It would thus have been conceivable that the performance of his population sample was above the standardization data. The data of both studies therefore confirm the findings of Pfüller and Zerahn-Hartung that the results in standardized achievement tests deteriorate over longer periods of time Pfüller &Zerahn-Hartung, 1996 . Furthermore the studies' results are in accordance to the German results of the Third International Mathematics and Science Study (TIMSS). The authors found that the German students reached the mean international results in mathematics on average 6 to 12 months later than their international peers Baumert, Lehmann, &u.a., 1997 .
But the difference between the performance of both population samples is too salient, and the temporal difference in the test application does not seem to suffice as a solitary rationalization. As explained in chapter 3.3., our data of the city population sample do seem to be indicative of genuine lack in academic performance, whereas the performance results of the rural population sample merely
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could be better, but are in the average range. One difference between the populations was that the rural study population consisted exclusively of East German students as well as its teachers who were all trained in the former German Democratic Republic (GDR). In the teacher's education of the GDR teaching methods like pattern drill were emphasized and high standards of broad knowledge were implicated for all students. Those methods and goals had become unpopular in West Germany during the nineteen-seventies and eighties, and there was a stronger focus on the individual achievement of each student. In the aforementioned TIMSS the authors found that a combination of both methods, as applied in many Asian countries, seems to produce the best results: to focus on the individual's achievement level in combination with ambitious educational intentions and consequent training. The authors infer that the individualization in Western European schooling has led to lowered expectations on the student's academic achievement and found a slight tendency toward better achievement in East German students Baumert, Lehmann, 1997 . At the same time these differences abide with time and none the probands of both studies had a conscious socialization in the GDR. The diminution of the East-Western difference was also noted in the TIMSS as this difference was more pronounced in older students who had more of their education in the former East Germany. In addition we found no difference in the city population sample between classes from the former West Berlin or East Berlin or between classes taught by teachers from either part of Germany. So differences in teaching methods between the formerly two countries fail to provide an explanation.Another contributing factor to the stronger performance of the rural population is possibly the absence of students whose native language is not German in the sample of Häußer. In such classes, the teaching of academic skills in German is facilitated especially at the beginning of the schooling and thus could make for an educational advantage.
Other explanations are conceivable, such as a lower motivation of the inner-city population for education, a higher stimulus density in urban areas leading to an overflow of information or various environmental influences such as nutrition and air pollution. These factors were not controlled for in either of the two studies.
A common feature of both studies is that only one fifth of the probands (one in the present, two in Häußer‘s study) whose parents agreed to a clinical and neuropsychological validation process were found to meet the ICD-10 criteria for a Specific disorder of arithmetical skills, although the majority of the probands (four in the present, six in Häußer‘s study) was found to have significant and marked difficulties in their arithmetical performance.
The most important common feature of both studies is a prevalence rate of 6.6 % for a suspected Specific disorder of arithmetical skills according to the diagnostic guidelines of the ICD-10. This coincides with the findings of the publications by Kosc and Gross-Tsur et al. who both used a methodology and criteria similar to those of the study of Häußer and the present study for diagnosing a Specific disorder of arithmetical skills. The authors so arrived at a prevalence rate for the condition of 6.4 % and 6.5 %, respectively Kosc, 1974 ; Gross-Tsur, Manor, 1996 . This is a striking similarity,
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especially since these prevalence rates were found over a period of more than 20 years in three different countries with unrelated languages using different tests.© Die inhaltliche Zusammenstellung und Aufmachung dieser Publikation sowie die elektronische Verarbeitung sind urheberrechtlich geschützt. Jede Verwertung, die nicht ausdrücklich vom Urheberrechtsgesetz zugelassen ist, bedarf der vorherigen Zustimmung. Das gilt insbesondere für die Vervielfältigung, die Bearbeitung und Einspeicherung und Verarbeitung in elektronische Systeme.
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