Verbal - Performance IQ Discrepancies in Children attending a Child and Adolescent Psychiatry Clinic

DANIEL VINCENT RIORDAN
SPECIALIST REGISTRAR,
NEW CRAIGS HOSPITAL,
INVERNESS,
IV3 8NP,
SCOTLAND.

• Objective
• Introduction
• Method
• Results
• Discussion
• Conclusion
• References
• Previous Page

ABSTRACT

OBJECTIVE: There is conflicting evidence regarding the relationship which verbal-performance IQ discrepancies have with hyperactivity and conduct problems in children. This study aims to determine if there is a relationship between the magnitude of such discrepancies in children and reported features of hyperactivity, conduct disorder and emotional disorder respectively.
METHOD: Case notes of children who had attended a Child and Adolescent Psychiatry clinic were retrospectively examined. Where the relevant data was available, verbal-performance IQ discrepancies were correlated with hyperactivity, conduct and emotional sub-scores respectively (as measured by parent and teacher questionnaires) by calculating Spearman rank (i.e. non-parametric) co-relation coefficients.
RESULTS: Boys were more likely than girls to have been referred for psychometrics (p < 0.05). Verbal-Performance IQ discrepancies were more likely to be in favour of verbal (p < 0.05). A weak (r=0.276) but statistically significant (p<0.02) correlation was found between these discrepancies (towards verbal) and hyperactivity sub-scores, but not with emotional or conduct sub-scores.
CONCLUSION: Low performance (relative to verbal) IQ is associated with reported hyperactivity in children, but not with conduct or emotional disorders

INTRODUCTION

Psychometric tests which produce an intelligence quotient (IQ) are constructed such that, theoretically, the population mean IQ is 100, with a standard deviation of 15 (Weschler, 1992). The expected population mean of both verbal (VIQ) and performance (PIQ) sub-tests is also 100, hence the expected discrepancy between sub-tests in a large enough, normal, population is zero. Whereas an individual discrepancy of 9 ( p < 0.05 ) to 12 ( p < 0.01 ) is statistically significant, an individual discrepancy is not usually considered clinically significant unless it is greater than 15 (Weschler, 1981; Kaufman, 1990).

Brumbach (1985) reported a significant association between depression and PIQ deficits (i.e. VIQ > PIQ) in children with learning difficulties. Although a latter study (Mokros et al, 1989) failed to replicate these results, such a deficit in PIQ has also been demonstrated in a population of adults with a diagnosis of depression (Sackein et al, 1992). A discrepancy towards verbal (VIQ > PIQ) has also been linked with Asperger's syndrome but not with other pervasive developmental disorders (Ehlers et al, 1997).

A link between discrepancies towards performance (i.e. VIQ < PIQ) and delinquency in children or dissocial personality disorder in adults has been demonstrated by several studies (Walsh et al, 1986; Walsh et al, 1987; Snow et al, 1997) although it has also been argued that a discrepancy in children in either direction is a useful predictor of the possibility of becoming delinquent in later life (Walsh, 1992).

Despite this apparent link between verbal-performance IQ discrepancy and conduct disorder, links with hyperactivity are less clear. Although hyperactivity in children has been associated with difficulties with both reading (Schachar et al, 1995; August et al, 1990) and motor co-ordination (Blonbis, 1999; Piek et al, 1999), no clear association has been demonstrated between hyperactivity and VIQ-PIQ discrepancies. A large epidemiological study of children on the Isle of Wight (Schachar et al, 1981) found that children who were pervasively hyperactive, (i.e. reported as hyperactive by both parents and teachers) had lower mean 'non-verbal' (analogous to performance) IQ than verbal IQ. No such discrepancy between non-verbal and verbal IQ was seen in children who were reported to be hyperactive in one setting only (school or home) or in 'non hyperactive' children.

This study did not use modern DSM-IV (American Psychiatric Association, 1994) or ICD-10 (World Health Organisation, 1992) criteria, such as the DSM-IV criteria for 'attention deficit and hyperactivity disorder' (ADHD) or the ICD-10 criteria for hyperkinetic disorders. Instead, children were considered to be "hyperactive" if they scored above a certain cut off point on a parent, or teacher, child behaviour inventory. A more recent work (Njiokiktjien et al, 1998) which compared a group of children with very large (i.e. >25) VIQ-PIQ discrepancies towards verbal with a group of children with equally large discrepancies towards performance found a higher incidence of ADHD in the VIQ >> PIQ group than in the PIQ >> VIQ group. The authors argue that this is evidence in favour of a right hemisphere theory of hyperactivity, which links attention deficit to right cerebral hemisphere dysfunction, which in turn , it is argued is linked to relatively low PIQ (Kaufman, 1990; Njiokiktjien et al, 1998).

However, the WISC-lll standard sample (Weschler, 1992) which provides the normal data on which one of the most commonly used psychometric test is based, contained a sample (n=68) of children who fulfilled DSM-lV criteria for ADHD. This sample did not show any significant difference between verbal and performance IQ.

NOTE ON TERMINOLOGY

Regarding diagnosis, for clarity, the DSM-IV term "ADHD" is favoured over the ICD 10 term "hyperkinetic disorder" in the remainder of this text. However the term "hyperactivity" is used to describe the trait which the hyperactivity sub-scale of the questionnaires used in this study were designed to measure.
AIM

Previous studies have tended to confine themselves either to individuals with very large discrepancies (Njiokiktjien et al.., 1998) or have compared individuals who satisfied predefined diagnostic criteria with normal populations (Weschler, 1992). This study aimed to determine if there is an association between the magnitude of VIQ - PIQ discrepancies in a (clinic referred) population (n = 77) and the reported severity of features suggestive of three common psychological problems of childhood: Hyperactivity, Conduct disorder and Emotional disorder respectively. It was hoped to establish what relationship, if any, exists between the VIQ - PIQ discrepancies (no matter how small or insignificant on the individual level) and the corresponding score which indicates the degree to which each child is reported to exhibit features of each of the three disorders. In this way the study is independent of arbitrarily defined inclusion or exclusion criteria.

METHOD

SUBJECTS

All case notes held at a department of Child and Adolescent Psychiatry (St. Finbarr's Hospital, Cork, Ireland) were reviewed. All children and adolescents whose case notes contained emotional screening forms completed by both parents and teachers as well as a WISC-lll (UK) psychometric assessment report were selected for inclusion in the study. All psychometric assessments had been carried out because they were considered clinically indicated at the time. They were conducted by 17 different clinical psychologists, some of whom were working within the clinic, the rest for other services.
Children who had been referred to the Child and Adolescent Psychiatry clinic but who had never actually attended were excluded.

DATA COLLECTION

Tick the box which best describes the child’s behaviour over the past three months (parents) / this school year (teachers). (rated 0, 1 or 2, and also similarly for items in tables below)

 

1	Very restless, has difficulty staying seated for long.
2	Squirmy, fidgety child.
3	Cannot settle to anything for more than a few moments.

 

Table 1 (above). Items comprising the hyperactivity sub-scale.

 

1 a (parents) 1b (teachers)	* Does he/she ever steal things? Has stolen things on one or more occasions in the past twelve months.
2	Frequently fights or is extremely quarrelsome with other children.
3	Is often disobedient.
4	Often tells lies.
5	Bullies other children

 

* On the parent questionnaire the options for this item read ; "No" (score 0), "Yes occasionally"(score 1) and "yes frequently" (score 2).

 

Table 2 (above). Items comprising the conduct sub-scale.

1	*Has tears on arrival at school or refused to go into the building in the past twelve months (parents) / in this school year (teachers).
2	Often worried, worries about many things.
3	Often appears miserable, tearful or distressed.
4	Tends to be fearful or afraid of new things or new situations.
*	* On the parent questionnaire the options to this item are; "Never" (score 0), "Occasionally but not as often as once a week" (score 1) or "at least once a week" (score 2)

 

Table 3 (above). Items comprising the emotional sub-scale.

On referral to the clinic, emotional screening forms had been routinely sent to each child's parents and (pending parental permission) teachers. The forms used were those designed by Rutter (RUTTER A and RUTTER B). These each contained three items relating to hyperactivity (Table 1), six items relating to conduct disorder (Table 2) and four items relating to emotional disorder (Table 3). As each item could be scored from 0 to 2, where both parent and teacher forms had been completed, it was possible to give the child a "hyperactivity score" on a scale of 0 to 12, a "conduct score" of 0 to 24 and an "emotional score" of 0 to 16 (Schachar et al., 1981).

As all of the children included in the study had reports on psychometric assessments included in their case notes, a note was made of the verbal and performance IQ score in each case. WISC-lll (UK) assessments only were included.

Where more than one completed parent or teacher form or more than one WISC-lll (UK) assessment existed, the most recent data available was used, earlier data being ignored.

ANALYSIS

As well as determining such characteristics of the sample population as sex ratio and mean full scale IQ (FSIQ), the data analysis also sought to determine if any association existed between VIQ-PIQ discrepancies and hyperactivity, conduct and emotional scores respectively. Two Spearman rank correlation coefficients (rs) were calculated for each disorder. One correlated the children's scores for each disorder with the absolute magnitude of their VIQ-PIQ discrepancies, regardless of the direction of the discrepancy. The other correlated the scores with the magnitude of the discrepancies towards verbal.
I.E. Performance IQ was subtracted from verbal IQ. In the former case sign was ignored and the cases ranked from greatest to least discrepancy, regardless of which direction the discrepancy was towards. In the latter, the sign was not ignored, hence cases were ranked from greatest negative value (greatest discrepancy towards performance) through to greatest positive value (greatest discrepancy towards verbal).

RESULTS

SAMPLE SIZE, SEX RATIO

267 case notes were identified of children who had been seen at the Child and Adolescent Psychiatry clinic and who had both parent and teacher emotional screening forms completed . Of these, 165 were male and 102 were female. 77 of these children had a report on a WISC-III (UK) psychometric assessment contained in their case notes, 60 of whom were male and 17 of whom were female. These 77 children comprised the sample population. This represents a male: female ratio of 1.62: 1 among the larger group of children referred to the clinic, rising to 3.53: 1 among those who had also been referred for psychometrics (the sample population).
A x 2 test on this data showed this difference in sex ratios to be statistically significant (X2 = 9.96, p < 0.001) meaning that boys were significantly more likely to have been referred for (WISC-III (UK)) psychometric evaluation than girls were, a difference which could not be accounted for solely by the higher male: female ratio in the larger group.

AGE

The 77 children who had both completed emotional screening forms and WISC-III assessments in their notes ranged in age from 6 years 6 months to 16 years and 11 months, (mean 11.03 years, s.d. 2.95).

WISC-III IQ

The mean full FSIQ of the sample was 83.9 (s.d. 15.56). This is a little more than one standard deviation below the expected population mean (by definition 100). On comparing this sample mean and s.d. with the population mean using a one sided t - test, t = 9.07. At 76 degrees of freedom (d.f.) this indicates a highly significant (p > 0.001) difference between the sample and population means.

VERBAL - PERFORMANCE IQ DISCREPANCIES

The mean VIQ - PIQ discrepancy of the sample population was 7.2 towards verbal. Using a t-test this is found to be significantly (t = 5.71, p < 0.001) different than the expected value (i.e. 0), demonstrating that this sample of children, attending a Child and Adolescent Psychiatry clinic, have a greater than expected tendency to have a VIQ - PIQ discrepancy towards verbal.

 

HYPERACTIVITY SUBSCORE	VIQ - PIQ DISCREPANCIES
0	-9, 10, 30
1	-9, -3, -3
2	-8, -4, 9, 18
3	-8, -3, 7, 11
4	-20, 14, 22
5	-17, 4, 9, 9, 9, 36
6	-2, 0, 7, 9, 12, 12, 12, 21
7	-17, -1, -1, 5, 6, 18, 19
8	-7, -3, 1, 1, 8, 9, 9, 12, 13, 20
9	-10, -3, 5, 9, 11, 11, 19, 19
10	-3, 0, 7, 7, 10, 11
11	-13, 0, 5, 10, 20
12	5, 13, 13, 13, 15, 17, 19, 23, 25, 32

 

TABLE 4 ( above). Verbal - Performance IQ discrepancies listed according to the corresponding hyperactivity sub-score. A negative value indicates a discrepancy in favour of performance, a positive value indicates a discrepancy in favour of verbal.

 

CONDUCT SUBSCORE	VIQ - PIQ DISCREPANCY
0	-9, -8, 4, 7, 10, 11, 23
1	-3
2	-8, -3, -3, -3, 7, 14
3	-9, -1, 9, 9, 22,
4	-1, 9, 9, 18, 30
5	-17, -4, 9, 12, 19, 36
6	-7, 15, 18
7	5, 13, 20
8	1, 9, 11, 12, 21
9	-17
10	0, 5, 7
11	6, 12
12	-3, 1, 20
13	0, 13, 19, 25
14	-20, 8, 13
15	-10, 5, 9, 11, 19
16	5, 10, 19
17	-3
18	-2, 10, 11
19	0, 9, 13
20	-13, 7
21	17
22	-
23	12
24	32

 

TABLE 5 (above). Verbal - Performance IQ discrepancies listed according to corresponding conduct sub-score. Negative values indicate a discrepancy in favour of performance, positive values indicate a discrepancy in favour of verbal.

 

EMOTIONAL SUBSCORE	VIQ-PIQ DISCREPANCY
0	5, 7, 9, 36
1	1, 6, 9, 11
2	-20, 5, 11, 12, 13, 13, 20, 30
3	-3, -3, -2, 0, 5, 11, 12, 13, 17, 19
4	-4, -1, 7, 9, 10, 19, 19, 19, 25
5	-9, -8, -8, 0, 0, 12, 14, 18, 21
6	4, 7, 10, 11, 20, 23
7	-17, -13, -9, -3, -3, 5, 8, 9, 10, 12, 18
8	-3, -3, 1, 7, 15, 32
9	-17, 9
10	-10, -7, 9, 9, 9
11	13, 22
12	-1
13	_
14	_
15	_
16	_

 

TABLE 6 (above). Verbal - Performance IQ discrepancies listed according to the corresponding emotional sub-score. A negative value indicates a discrepancy in favour of performance, a positive value indicates a discrepancy in favour of verbal.

 

The VIQ - PIQ discrepancies for each of the 77 cases are listed, according to the corresponding hyperactivity score in Table 4, conduct score in Table 5 and Emotional score in Table 6. A positive discrepancy score indicates a discrepancy towards verbal, a negative score indicates a discrepancy towards performance.

Correlation coefficient			t	p
Hyperactivity	(absolute)	0.16	1.24	0.5 > p > 0.1
	(towards verbal)	0.27	2.48	p < 0.02
Conduct	(absolute)	0.03	0.32	0.5 > p > 0.1
	(towards verbal)	0.09	0.86	0.5 > p > 0.1
Emotional	(absolute)	0.09	0.76	0.5 > p > 0.1
	(towards verbal)	-0.18	1.64	0.5 > p > 0.1

 

 

Table 7: Correlation coefficients (with corresponding t - values and p - values at 76 degrees of freedom) relating hyperactivity, conduct disorder and emotional disorder with VIQ - PIQ discrepancies, both absolute and towards verbal.

 

The Spearman rank (i.e. nonparametric) correlation coefficients (rs) comparing the VIQ-PIQ discrepancies with the corresponding hyperactivity, conduct and emotional scores are given in Table 7 together with corresponding t values (76 d.f.) and p values, both for absolute discrepancies and discrepancies towards verbal.

The correlation coefficient in the case of hyperactivity scores with discrepancies towards verbal (rs = 0.276) indicates a weak, but statistically significant, (t = 2.324, p < 0.02 at 76 d.f.) correlation between VIQ-PIQ discrepancy (towards verbal) and subjective parent / teacher ratings of hyperactivity. However, when the sign was ignored, rs fell to 0.16 (t=1.41, p > 0.1) indicating no significant correlation with absolute VIQ-PIQ discrepancy.

In the case of conduct disorder, the correlation coefficients, rs = 0.099 (towards verbal) and rs = 0.037 (absolute) are much smaller. Neither are statistically greater than 0 , hence no association was demonstrated between VIQ - PIQ discrepancy (either absolute or towards one direction) and conduct disorder.
The correlation coefficients in the case of emotional difficulties is also small, rs = -0.187 (towards verbal) and rs = 0.087 (absolute). These too do not differ significantly from zero, again demonstrating no significant association between emotional difficulties and VIQ - PIQ discrepancies.

DISCUSSION

LIMITATIONS

A. SELECTION BIAS

The group studied was not a random sample but consisted of children who had attended a Child and Adolescent Psychiatry clinic and who had had a psychometric evaluation. Therefore, children who had a low score in one, two or even all three disorder groups studied can not be considered to comprise a normal control group. It should also be noted that this study is confined to a group of children who had been referred for psychometric assessment on clinical grounds, i.e. in most cases a low FSIQ or a sub-score discrepancy of some form had been suspected. This is reflected in the low mean FSIQ of the sample population.

It is also worth noting the high male: female ratio in the study group. This ratio was demonstrated to be significantly greater than the male: female ratio of the group of children who differed from the study group only in that they had not been referred for psychometrics. This suggests that boys referred to a Child and Adolescent Psychiatry clinic are more likely to be referred for psychometrics than girls are. This in itself is an interesting and unexpected finding, which indicates a sex bias in the selection criteria. It is interesting that this male: female ratio (3.53: 1) is comparable with the reported male: female ratio of children presenting with hyperactivity (3.6: 1) (Taylor, 1986).

B. VALIDITY

The validity of this study relies firstly on the assumption that the WISC III (UK) standardisation sample and (UK) norms are applicable to the Irish population under study, an assumption which may not be accurate on account of the considerable differences in the education systems of the two countries. Secondly, it relies on the assumption that a child's score for each symptom group on the "Rutter questionnaire" accurately reflects the degree to which that child is presenting with the corresponding disorder. It is worth noting that one of the few previous studies to have linked hyperactivity with a relatively high verbal IQ (Schachar et al., 1981) used the same instrument to measure hyperactivity as this study.

The use of a scoring system for each symptom group has the disadvantage of not producing results based on ICD-10 or DSM-1V diagnostic criteria. It is thus important to note that, for example, a child scoring a maximum score on the hyperactivity sub-scale (12/12) may not necessarily fulfil the DSM-lV diagnostic criteria for ADHD, (although, in practice, one would expect this to be unlikely). Nevertheless, the use of a well recognised and widely used method of quantifying the degree to which traits suggestive of each disorder are reported to be present allows the data to be correlated with other quantified (i.e. psychometric) data, without the use of arbitrarily defined cut-off points.

VIQ-PIQ DISCREPANCIES

In a normal population, the expected mean VIQ-PIQ discrepancy is zero (Weschler, 1992). However in this sample there is a clear tendency for VIQ to be higher than PIQ among all children seen at the clinic. It may be that low performance IQ children are more likely to be referred to a Child and Adolescent Psychiatry clinic whereas children with low verbal IQs may be more likely to be seen by another service. For example, children with low verbal IQs may present earlier in life, perhaps due to a speech delay, and be referred to speech therapy rather than to Child and Adolescent Psychiatry.
The tendency for VIQ to be greater than PIQ among a Child and Adolescent Psychiatry clinic population was found to correlate only with reported hyperactivity, not with conduct or emotional difficulties.

CONCLUSION

These results suggest that hyperactivity in children is associated with relatively low performance IQ, whereas conduct and emotional problems are not. It should be noted, of course, that given the low (albeit statistically significant) rs value, VIQ-PIQ discrepancy on its own as "a test for ADHD" would have both poor sensitivity and specificity. However, these results indicate that, in individual cases, such discrepancies may provide evidence in favour of a hyperactivity component to a conduct disorder, the weight of evidence being proportional to the magnitude of discrepancy towards verbal.

These results are consistent with the findings of the Isle of Wight study (Schachar et al, 1981) using the same parent and teachers rating scales but are, however, not consistent with studies linking VIQ-PIQ discrepancies with delinquency in children, as no association was found between such discrepancies and conduct disorder.

These results support the right hemisphere theory of attention (Garcia et al, 1997), but only insofar as there is evidence that PIQ and VIQ reflect right and left hemispheric function respectively. Although observations and tests on patients with known localised brain injuries have linked verbal ability with the left hemisphere and performance with the right (Kaufman, 1990), some authors suggest that, whereas a low VIQ relative to PIQ may be an accurate indicator of left hemisphere dysfunction, a low PIQ relative to VIQ is a more non-specific indicator of brain damage or dysfunction (Warrington et al, 1986: Whelan et al, 1998).

These findings are also of interest in the context of the relationship between ADHD, dyspraxia and dyslexia. Relatively low VIQ has been considered an indicator of dyslexia and relatively low PIQ of dyspraxia (Weschler, 1992) ). In recent years, researchers in this field have begun to notice a high degree of individual and familial comorbidity between these three disorders (Stordy, 1999).

Traditionally ADHD has been seen as the responsibility of Child Psychiatry, dyspraxia of Occupational Therapy and dyslexia of Speech Therapy or Educational Psychology, possibly resulting in common features between all three being under-recognised. Evidence is emerging (Richardson et al, 1997) that a phospholipid membrane defect may provide a common biological link between several neurodevelopmental and learning disorders, which has raised questions about the validity of our current diagnostic concepts of hyperkinetic disorders / ADHD, dyslexia and dyspraxia. In the light of this debate, these results suggest that there may be a greater overlap between ADHD and dyspraxia than between these two disorders and dyslexia. However, in making any such interpretation, the comments above regarding referral bias and the historical tendency for children with dyslexia to be referred elsewhere need to be borne in mind. This is particularly important given the strikingly small number of children with PIQ > VIQ identified in this Child and Adolescent Psychiatry population. It should also be considered that some authors have seriously questioned the diagnostic usefulness of IQ discrepancies in dyslexia and dyspraxia. It may therefore be unwise to make any inferences from this data relating to these disorders (Fletcher et al, 1998: Lyon et al, 1996).

Further work needs to be done to determine if these findings can be replicated in children with higher FSIQs. It also needs to be established whether children with mild VIQ-PIQ discrepancies in favour of performance differ from those with discrepancies in favour of verbal, in terms of emotional and behavioural difficulties. This study tells us little about the former, as so few children with such an IQ discrepancy were identified in this sample.

ACKNOWLEDGEMENTS

The author wishes to thank the staff of the Child Guidance Clinic, St Finbarr's Hospital, Cork, Ireland, for their help and encouragement, in particular Dr Finbarr O' Leary, Consultant Child and Adolescent Psychiatrist, Dr Pat Corbett, Clinical Psychologist and Ms. Deirdre Hegarty, Occupational Therapist.

 

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DECLARATION OF COMMERCIAL INTERESTS
None.

ETHICS / CONSENT

The retrospective use of the patient data involved in this project was approved by the Cork University / Southern Health Board Medical ethics committee in January 1999.
On the advice of the ethics committee, the study design was also discussed with the Data Protection Commissioner. Following this, it is my understanding that the study complies with the (Republic of Ireland) Data Protection Act, 1988.

Version 1.0 Published 1/1/2001

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