This study aimed to compare the Wechsler Intelligence Scale for Children, Fourth Edition (WISC-IV) profiles of children with attention deficit/hyperactivity disorder (ADHD) and typically-developing children (TC) in Korea.
The Korean version of the WISC-IV and the Advanced Test of Attention (ATA) were administered to 377 children and adolescents: 224 with ADHD (age 8.2±2.1 years, 182 boys) and 153 TC (age 8.7±2.4 years, 68 boys). Partial correlation and an analysis of covariance were used to investigate the relationship between the scores of the WISC-IV and the ATA.
The mean score of the full-scale intelligence quotient was lower in ADHD children than in TC (p<0.001). In analyses controlling for gender and with the full-scale intelligence quotient as a covariate, the working memory index (WMI) (p<0.001) and values of the Digit span subtest (p=0.001) of the WISC-IV were lower in the ADHD group than in TC. The WMI (r=-0.26, p<0.001) and its subtest Arithmetic scores (r=-0.25, p<0.001) were negatively correlated with Commission errors on the auditory ATA.
Children with ADHD have significantly lower WMI scores, which were clinically correlated with Commission errors on the auditory task of the ATA. Thus, the WMI is an indicator of attention deficit in children with ADHD.
Attention deficit/hyperactivity disorder (ADHD) is one of the most common psychiatric conditions of children and adolescent, which has a prevalence of 5% to 8% [
Although there are no objective diagnostic tests for ADHD, intelligence tests, including the Wechsler Intelligence Scale for Children (WISC), are widely used to evaluate the cognitive function in children with ADHD. Children with ADHD demonstrate lower intellectual ability than typically-developing children (TC). A meta-analysis showed that the average full-scale intelligent quotient (FSIQ) in children with ADHD is 7–10 points below the mean of the comparison group [
The fourth edition of the WISC (WISC-IV; 2003) incorporates the expanded understanding of development and cognitive neuroscience since the publication of the WISC-III (1991) [
Previous study identified 89% of children with ADHD from TC via assessments of Digit span, Information, Vocabulary, and Picture completion using the WISC-III [
To better assess the diagnostic value of the WISC-IV for children with ADHD, we used the Korean version of the WISC-IV (K-WISC-IV), standardized and released in 2011, to compare Korean ADHD children with TC. We also investigated the correlation between indices and scales of the WISC-IV and the scores of the computerized continuous performance test (CPT) to investigate what elements of the WISC-IV reflect core attentional deficits of ADHD.
Subjects with ADHD were prospectively enrolled from September 2012 to May 2018 on the Department of Pediatric Psychiatry of Asan Medical Center, located in Seoul, South Korea. To include of the study, ADHD subjects had to be from 6 to 12 year-old age and diagnosed ADHD according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) and the Kiddie Schedule Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime version (K-SADS-PL), whereas TC subjects had to be from 6 to 12 years of age and not ever meet the criteria for a diagnosis of ADHD. TC subjects were recruited by advertisements on the staff board at Asan Medical Center.
Participants were excluded from this study when they had any of the following exclusion criteria: 1) IQ score lower than 70 according to the K-WISC-IV, 2) any history of schizophrenia, organic mental disorder, and pervasive developmental disorder 3) any history of other neurological disorders including seizure, 4) presence of impairments in any sensorium, and 5) lifetime history of taking stimulants or atomoxetine more than 3 months or history of taking any psychotropic drug within the last 6 months.
The study received ethical approval from the Institutional Review Board in Asan Medical Center (2012-0767). Informed consent was obtained from the parents of all children included in the study, and assent/consent was obtained from all children.
ADHD and other psychiatric comorbidities of both ADHD and TC subjects were diagnosed by certified child and adolescent psychiatrists (H.W.K., H.J.L., and K.J.P.), and psychiatric diagnosis of these conditions were also confirmed by K-SADS-PL [
The K-WISC-IV, standardized by Kwak et al., [
The Advanced Test of Attention (ATA) is a type of computerized continuous performance test developed and standardized in South Korea [
Statistical analyses were performed using R (3.5.1) with R studio (1.0.153). The normality of data was assessed by Shapiro-Wilk tests. Results from the ADHD group and TC were compared with chi-square tests, Fisher’s exact tests, Student’s t-tests, and analyses of covariance, adjusted for FSIQ and gender. Partial correlation analyses were used to determine the relationship among the scores of WISC-IV indices and subtests and ATA scores, adjusted for FSIQ and gender.
The characteristics of children with ADHD and TC are presented in
The mean FSIQ was significantly lower in the ADHD than in the TC group (p<0.001) (
We further dissected the difference between the groups for the Digit span subtest within the WMI of the K-WISC-IV. The mean scores for Digit span forward (p=0.041) and backward (p=0.114) did not differ between the ADHD and TC groups after controlling for FSIQ and gender and correcting for multiple comparisons (
To investigate which factor of the K-WISC-IV would be affected by the attentional abilities of the ADHD group according to the ATA, we performed partial correlation analyses with adjustments for FSIQ and gender. Only WMI showed a meaningful negative correlation (|r|>0.2) with Commission errors on the auditory tasks of the ATA (r=-0.26, p<0.001) (
In our study, children with ADHD showed lower scores for the FSIQ, WMI, and Digit span subtests of the K-WISC-IV. In addition, the WMI score and Arithmetic subtest score of the WISC-IV correlated negatively with Commission errors on the auditory task of the ATA. In our previous retrospective chart review, we reported that children with ADHD showed low average scores in WMI and PSI which were clinically correlated with ATA scores [
Our results are consistent with several previous findings showing that children [
We also found that WMI scores negatively correlated with scores of Commission errors on the auditory ATA but not with Omission errors. Although both types of errors are associated with inattention, hyperactivity, and impulsivity, Commission errors is considered to measure response inhibition whereas Omission errors measure selective attention [
Among the subtests included in the WMI, the score for the Digit span subtest were decreased in children with ADHD compared with TC, consistent with a previous study [
Several limitations should be considered when interpreting our results. First, ADHD is more prevalent in boys, and a gender difference was expected and can be a marker of a reliable and representative cohort [
In summary, we investigated the demographic and cognitive characteristics of children with ADHD using the K-WISCIV, ADHD Rating Scale, and ATA. The results of this study show that working memory is impaired in children with ADHD and can be assessed with the WMI of the WISC-IV.
This work was supported by a National Research Foundation of Korea (NRF) grant (no. 2018R1A2B6002216) funded by the Korean Government (Ministry of Science and ICT).
The authors have no potential conflicts of interest to disclose.
Conceptualization: Hyo-Won Kim, Min Kyung Koh. Data curation: Go Eun Yu, Yangsik Kim, Kee Jeong Park, Hyun-Jeong Lee. Formal analysis: Yangsik Kim, Hyo-Won Kim. Funding acquisition: Hyo-Won Kim. Investigation: Min Kyung Koh, Kee Jeong Park, Hyun-Jeong Lee, Go Eun Yu, Hyo-Won Kim. Methodology: Yangsik Kim, Hyo-Won Kim. Project administration: Hyo-Won Kim. Resource: Min Kyung Koh, Kee Jeong Park, Hyun-Jeong Lee, Go Eun Yu, Hyo-Won Kim. Supervision: Hyo-Won Kim. Validation: Hyo-Won Kim. Visualization: Yangsik Kim, Hyo-Won Kim. Writing—original draft: Yangsik Kim, Hyo-Won Kim. Writing—review & editing: Yangsik Kim, Hyo-Won Kim.
Demographic and clinical characteristics of ADHD and TC subjects
Characteristic | ADHD (N=224) | TC (N=153) | t or χ2 | p-value |
---|---|---|---|---|
Age, years, mean (SD) | 8.2 (2.1) | 8.7 (2.4) | 1.83 | 0.104 |
Gender | ||||
Boys, N (%) | 182 (81.3) | 68 (44.4) | 55.10 | <0.001 |
Subtype, N (%) | ||||
Inattentive | 107 (47.8) | |||
Hyperactive/impulsive | 9 (4.0) | |||
Combined | 95 (42.4) | |||
NOS | 13 (5.8) | |||
Comorbid diagnosis, N (%) | 60 (26.8) | 16 (10.4) | ||
ODD |
25 (11.2) | - | 18.30 | <0.001 |
MDD |
3 (1.3) | 2 (1.3) | 0.00 | 0.979 |
Anxiety disorder | 13 (5.8) | 10 (6.5) | 0.09 | 0.770 |
Enuresis |
2 (0.9) | - | 1.37 | 0.240 |
Tic disorder | 21 (9.4) | 5 (3.2) | 5.28 | 0.022 |
ARS, mean (SD) | ||||
Inattentive | 29.1 (44.0) | 13.2 (41.0) | -17.4 | <0.001 |
Hyperactive/impulsive | 29.6 (38.9) | 11.9 (24.4) | -14.8 | <0.001 |
using Fisher’s exact test.
ADHD: attention deficit hyperactivity disorder, MDD: major depressive disorder, NOS: not otherwise specified, ODD: oppositional defiant disorder, TC: typically-developing children, ARS: ADHD rating scale
The K-WISC-IV and ATA scores of ADHD and TC subjects
Assessment | ADHD |
TC |
t or χ2 | p-value | Adjusted p-value |
||
---|---|---|---|---|---|---|---|
N | Mean (SD) | N | Mean (SD) | ||||
FSIQ | 95.4 (15.0) | 106.0 (13.6) | 7.04 | <0.001 | - | ||
VCI | 98.4 (12.9) | 103.7 (15.0) | 3.65 | <0.001 | 0.121 | ||
Similarities | 218 | 9.4 (2.0) | 152 | 10.6 (2.7) | 3.86 | <0.001 | 0.043 |
Vocabulary | 218 | 10.6 (2.7) | 152 | 11.2 (3.2) | 1.97 | 0.05 | 0.113 |
Comprehension | 218 | 9.0 (2.6) | 152 | 9.9 (2.9) | 3.06 | 0.001 | 0.856 |
PRI | 99.9 (16.2) | 107.9 (15.9) | 4.78 | <0.001 | 0.012 | ||
Block design | 218 | 10.5 (3.0) | 152 | 115. (3.1) | 3.08 | 0.008 | 0.356 |
Picture concepts | 176 | 9.4 (3.2) | 151 | 10.5 (3.2) | 3.22 | 0.003 | 0.024 |
Matrix reasoning | 217 | 9.8 (3.0) | 152 | 11.3 (2.9) | 4.75 | <0.001 | 0.030 |
Picture completion | 146 | 9.3 (2.6) | 78 | 10.3 (2.6) | 2.53 | <0.001 | 0.057 |
WMI | 96.1 (16.5) | 107.8 (13.6) | 7.2 | <0.001 | <0.001 | ||
Digit span | 218 | 9.5 (3.5) | 152 | 11.8 (2.8) | 6.65 | 0.003 | 0.001 |
Arithmetic | 164 | 9.1 (3.1) | 120 | 11.1 (2.9) | 5.55 | <0.001 | 0.114 |
PSI | 91.3 (14.7) | 99.2 (14.3) | 5.14 | <0.001 | 0.111 | ||
Coding | 218 | 8.3 (3.2) | 152 | 9.5 (2.9) | 3.44 | <0.001 | 0.496 |
Symbol search | 218 | 8.7 (2.8) | 152 | 10.2 (2.9) | 5.02 | <0.001 | 0.729 |
ATA visual | |||||||
Omission errors | 29.1 (44.0) | 13.2 (41.0) | -3.57 | <0.001 | 0.255 | ||
Commission errors | 29.6 (38.9) | 11.9 (24.4) | -4.96 | <0.001 | 0.883 | ||
Response time | 7.8 (15.3) | 6.1 (11.0) | -1.33 | 0.64 | 0.031 | ||
Response time variability | 19.9 (27.5) | 8.0 (25.7) | -4.32 | <0.001 | 0.359 | ||
ATA auditory | |||||||
Omission errors | 12.8 (24.7) | 7.7 (22.0) | -2.07 | <0.001 | 0.001 | ||
Commission errors | 14.7 (24.8) | 5.6 (17.6) | -3.93 | <0.001 | 0.080 | ||
Response time | -3.2 (12.5) | 0.4 (8.0) | 3.08 | 0.034 | 0.543 | ||
Response time variability | 0.04 (11.1) | -3.2 (9.0) | -2.93 | 0.005 | 0.149 |
Multiple comparison corrected significance level p<0.002.
adjusted for FSIQ and gender. Different number of subtests of K-WISC-IV due to children’s developmental stages.
ATA: Advanced Test of Attention, K-WISC-IV: Korean–Wechsler Intelligence Scale for Children, Fourth Edition, FSIQ: full-scale intelligent quotient, VCI: verbal comprehension index, PRI: perceptual reasoning index, WMI: working memory index, PSI: processing speed index, TC: typically-developing children
The K-WISC-IV Digit span scores of ADHD and TC
Digit span | Mean (SD) score |
p-value | Adjusted p-value |
|
---|---|---|---|---|
ADHD (N=179) | TC (N=132) | |||
Forward | 10.0 (3.6) | 11.9 (2.8) | <0.001 | 0.041 |
Backward | 9.0 (3.6) | 10.6 (3.1) | <0.001 | 0.114 |
Multiple comparison corrected significance level, p<0.025.
adjusted for FSIQ and gender.
ADHD: attention deficit/hyperactivity disorder, K-WISC-IV: Korean–Wechsler Intelligence Scale for Children, Fourth Edition, TC: typically-developing children, FSIQ: full-scale intelligent quotient
Partial correlation analyses among four indexes of KWISC-IV and ATA, adjusted for FSIQ and gender
Assessment | VCI | PRI | WMI | PSI |
---|---|---|---|---|
ATA visual | ||||
Omission errors | 0.09 | 0.02 | -0.11 |
-0.02 |
Commission errors | 0.07 | -0.65 | -0.04 | 0.02 |
Response time | 0.10 | 0.06 | 0.03 | -0.20 |
Response time variability | 0.11 |
-0.04 | <0.01 | -0.09 |
ATA auditory | ||||
Omission errors | <0.001 | 0.75 | -0.12 |
<0.01 |
Commission errors | 0.17 |
-0.01 | -0.26 |
0.03 |
Response time | -0.10 | 0.58 | 0.14 |
-0.07 |
Response time variability | 0.03 | 0.04 | -0.10 | 0.02 |
p<0.05,
p<0.01,
p<0.001.
ATA: Advanced Test of Attention, K-WISC-IV: Korean–Wechsler Intelligence Scale for Children, Fourth Edition, VCI: verbal comprehension index, PRI: perceptual reasoning index, WMI: working memory index, PSI: processing speed index, FSIQ: full-scale intelligent quotient
Partial correlation analyses among 14 subtests of K-WISC-IV and ATA adjusted for FSIQ and gender
K-WISC-IV subtests | ATA visual |
ATA auditory |
||||||
---|---|---|---|---|---|---|---|---|
Omission errors | Commission errors | Response time | Response time variability | Omission errors | Commission errors | Response time | Response time variability | |
Similarities | 0.04 | -0.02 | 0.12 |
0.02 | 0.05 | 0.03 | 0.02 | 0.03 |
Vocabulary | 0.11 |
0.11 |
0.05 | 0.12 |
-0.44 | 0.11 |
-0.08 | 0.03 |
Comprehension | 0.002 | 0.03 | 0.03 | 0.06 | 0.01 | 0.16 |
-0.13 |
0.01 |
Block design | 0.09 | 0.04 | 0.04 | 0.001 | 0.07 | 0.005 | -0.02 | 0.10 |
Picture concepts | -0.02 | -0.06 | 0.08 | -0.01 | 0.01 | 0.006 | 0.06 | 0.10 |
Matrix reasoning | -0.09 | -0.13 |
-0.04 | -0.10 | 0.07 | -0.09 | 0.11 |
-0.15 |
Picture completion | 0.001 | 0.003 | -0.04 | 0.06 | -0.12 | 0.08 | -0.04 | -0.05 |
Digit span | -0.06 | -0.02 | 0.02 | -0.02 | -0.09 | -0.14 |
0.10 | -0.07 |
Arithmetic | -0.11 | 0.02 | 0.03 | 0.07 | -0.09 | -0.25 |
0.08 | -0.38 |
Coding | -0.02 | 0.07 | -0.15 |
-0.04 | 0.003 | 0.004 | -0.09 | 0.06 |
Symbol search | -0.02 | -0.06 | -0.18 |
-0.11 |
0.001 | 0.05 | -0.01 | -0.02 |
p<0.05,
p<0.01,
p<0.001.
ADHD: attention deficit/hyperactivity disorder, ATA: Advanced Test of Attention, K-WISC-IV: Korean–Wechsler Intelligence Scale for Children, Fourth Edition, FSIQ: full-scale intelligent quotient