Utility of the Kyoto Scale of Psychological Development in cognitive assessment of children with pervasive developmental disorders

Authors


Tomonori Koyama, PhD, 4-1-1 Ogawa-Higashi, Kodaira, Tokyo 187-8553, Japan. Email: tomok@ncnp.go.jp

Abstract

Based on the clinical records of 74 children with pervasive developmental disorders (PDD; mean age, 45.2 months; 62 boys), the utility of the Kyoto Scale of Psychological Development in cognitive assessment of young and/or mentally retarded PDD children was investigated. Because the overall developmental quotient (DQ) had the highest correlation with the IQ (Pearson's r, 0.88) and the Cognitive–Adaptive DQ showed a non-significant difference in mean (65.8) from the IQ (66.4), they both seem useful as an equivalent to an IQ. The test would enable clinicians to carry out continual developmental assessments and to develop appropriate remedial programs for those children from infancy.

EARLY INTERVENTION IS important for children with pervasive developmental disorders (PDD) to enhance their social adaptation and to reduce difficulties in parenting.1–3 A cognitive assessment of PDD children is necessary to plan remedial treatment and predict outcomes of such children.4 It is not easy, however, to administer standardized intelligence tests to young and/or mentally retarded PDD children. Without reliable alternative tools, clinicians cannot trace developmental change in children and evaluate the effectiveness of treatment.

The Kyoto Scale of Psychological Development (K-test) is one of the most widely used developmental tests in Japan.5 Based on the Koyama et al. study written in Japanese,6 its developmental quotients (DQ) have been considered to be equivalent to an IQ of younger PDD children;4,7 but the K-test was recently revised.

In the present study we examined the utility of the revised version of the K-test in the cognitive assessment of young and/or mentally retarded PDD children. This article, a scientific confirmation written in English, would help Japanese researchers to introduce studies involving the K-test in international journals, and may stimulate Japanese studies focusing further on early development of PDD children.

METHODS

Instruments

Kyoto Scale of Psychological Development

The latest version of the K-test standardized for 2677 Japanese children/adults was published in 2002.5 The K-test is an individualized face-to-face test administered by experienced psychologists to assess a child's development in the following three areas: Postural–Motor (P-M; fine and gross motor functions); Cognitive–Adaptive (C-A; non-verbal reasoning or visuospatial perceptions assessed using materials [e.g. blocks, miniature cars, marbles]); and Language– Social (L-S; interpersonal relationships, socializations and verbal abilities). It usually takes approximately 20–40 min to administer.

In each of the three areas, a sum score is converted to a developmental age (DA), and an overall DA is also obtained. The three area DAs and the overall DA are divided by the child's chronological age and multiplied by 100 to yield four DQ.

Procedures and subjects

This study, approved by the ethics committee of Tokyo University Graduate School of Medicine when the first and the last authors were affiliated with the university, was conducted at a regional clinic in Tokyo specializing in PDD.

In the clinic, experienced psychologists performed cognitive evaluations according to the developmental level of the child. Some of the children, who had been assessed on the K-test when younger, were given the Tanaka–Binet Intelligence Scale (Japanese version of Stanford–Binet Intelligence Scale)8 when they grew up. For all those children, we obtained their last DQ and their first IQ from clinical records.

Previous studies confirmed the utility of other developmental tests through significant positive correlation between DQ and IQ,9,10 but confirmation may be insufficient because the difference between DQ and IQ was not examined on either mean scores or individual scores. We set three criteria for the DQ to be useful as an equivalent to IQ: (i) significant correlation with IQ (Pearson's r), (ii) non-significant difference from IQ (paired t-test), and (iii) sufficient number of children with DQ close to IQ (≤8 points: 0.5 SD of the IQ).8

The subjects were 74 children with PDD (mean age at K-test, 45.2 ± 18.6 months; range, 24– 137 months; 62 boys) with an ICD-10 diagnosis according to consensus of a clinical team consisting of professionals led by an experienced child psychiatrist (H.K.).

Statistical analysis

All statistical analyses were performed in SPSS 16.0J for Windows (SPSS Japan, Tokyo, Japan) and statistical significance was set at P < 0.01 (two-tailed).

RESULTS

Table 1 shows that all of the K-test DQ had significant positive correlation with the Tanaka–Binet IQ, and that overall DQ had the highest correlation. Significant correlations were maintained when converted to ranked scores, as examined by Delmolino.10

Table 1.  Kyoto Scale of Psychological Development scores in 74 children with PDD
 MeanSDCorrelation with IQ (Pearson's r)Mean difference from IQ (Paired t-test)% of children scoring close to IQ
(≤8 points)
  • *

    P < 0.01.

  • DQ, developmental quotient; PDD, pervasive developmental disorders.

Overall DQ63.116.70.88*2.88*59.5
Postural–Motor DQ79.121.00.59*5.84*12.2
Cognitive–Adaptive DQ65.816.50.81*0.4344.6
Language–Social DQ57.120.10.81*6.53*43.2
Tanaka–Binet IQ66.420.2   

The mean C-A DQ was almost equal to the mean IQ, with no significant difference between them. The mean overall and L-S DQ were significantly lower, and the mean P-M DQ was significantly higher than the mean IQ. A total of 59.5% of PDD children had an overall DQ close to his/her IQ.

DISCUSSION

The results showed that overall and C-A DQ seem useful. The DQ in the present study were highly correlated with IQ as compared to those on parental reports,9 which indicates that assessments carried out by professional observations are more appropriate to evaluate a child's continual development.

The mean overall DQ was significantly lower than the mean IQ, but the difference was very small. Its utility as an equivalent to IQ was confirmed in that it had the highest correlation with IQ and it was closest to IQ of the four DQ, in the highest percentage of children.

Consistent with the findings in the previous version of the K-test,6 C-A DQ was significantly correlated with IQ and the mean score was almost equal to the mean IQ. This means that clinicians can simplify cognitive assessments of the K-test by using the C-A subscale only. A large discrepancy between the IQ and the P-M or L-S DQ is not surprising because most children in the present study did not have any impairment in motor function but a significant impairment in communication.

Because an interval between the two tests might influence the results, evaluations done at the same period are methodologically ideal to test the association of DQ with IQ. Such an attempt, however, is impossible for IQ-unmeasurable children and should be avoided even in IQ-measurable children in clinical settings.

In conclusion, the K-test would enable clinicians to make continual assessments of young and/or mentally retarded PDD children from infancy, and to develop appropriate remedial programs for them, and to evaluate their effectiveness.

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