INSTABILITY OF THE INTELLIGENCE QUOTIENT-MOTOR QUOTIENT RELATIONSHIP Kevin N. Cole Susan R . Harris

Professionals serving children with developmental disabilities are faced with the task of classifying individuals as exceptional and allocating services to those who will benefit from intervention. Several disciplines use the student’s developmental profile as the basis for determining service eligibility. In speechlanguage pathology (for diagnosis of language delay) and remedial reading instruction (for diagnosis of learning disability), for example, performance in the particular domain is contrasted with performance on a measure of intelligence. The relationship between these two factors is then used to diagnose the disorder, and consequently to predict whether the student will benefit from intervention. It is presumed that cognition sets the upper limit for development (e.g. Cromer 1976), so students are not considered to have an aptitude for growth unless cognition is more advanced than the specific area of development. While this model of diagnosis and triage has been used for some time in other disciplines, it is a relatively new trend for the allocation of physical therapy (PT) and occupational therapy (OT) services to children (Carr 1989, Long 1990, Oringel 1990). This practice applied to motor development has been labeled ‘cognitive referencing’ (Cole et al. 1991). According to this method, children who

have equally delayed development in cognitive and motor skills are considered to be poor candidates for direct PTIOT intervention, while children with delayed motor skills but relatively higher cognitive abilities are considered to be appropriate candidates (e.g. Louisiana Department of Education 1987, Waukesha Delivery Model 1987, Washington Occupational Therapy Association 1988). For both reading and language, there are well-developed theoretical models suggesting a strong relationship between the skill area and cognitive development (e.g. Dale 1976, Rice 1983). For motor development, however, models explaining the causal relationship between skill, development and cognition have yet to be elucidated. Ironically, while PT and OT service providers are beginning to employ the cognitive referencing model, it is being strongly challenged in disciplines in which it has traditionally been used. The theoretical basis of cognitive referencing has been challenged in both the areas of reading (Siegel 1989, Stanovich 1991) and language intervention (Kemp 1983, Subcommittee on Language and Cognition 1987). Criticisms of assumptions underlying the cognitive referencing model include: (1) 1Q tests may measure intelligence too narrowly (Stanovich 1991); (2r IQ may not be independent of the contrasting skill area (Siegel 1989);

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(3) children with IQ scores higher than skill-area scores do not necessarily have different causal factors for delay in the skill area than children with less discrepant profiles (Leonard 1987); (4) children with IQ scores higher than skillarea scores do not necessarily have uniquely disordered information processing skills (Cole et al. 1990, Leonard 1991); and (5) IQ scores are poor predictors of intervention progress (Bruck 1988; Labuda and DeFries 1989; Cole et al. 1990, 1991; Notari et al. 1992). Advocates of cognitive referencing might argue that, despite potential flaws in the conceptual bases of the model, our ability to measure discrepancies between motor development and cognitive level allows us to identify groups of students who will particularly benefit from PT or OT services. The ability to measure accurately the relationship between IQ and other ‘developmental areas, however, has also been challenged for the areas of language and reading development (McCauley 1989, Lahey 1990). Frequently test instruments do not include children with disabilities in the norming sample (Fuchs et al. 1987), and some subgroups of children with disabilities respond in systematically different ways to assessment tasks and examiners (Fuchs 1981, Fuchs et al. 1983). Test reliability is also a concern in the implementation of the cognitive referencing model (McCauley 1989, Lahey 1990). Reliability of assessment tools is critical in cognitive referencing because the reliability of the difference between instruments influences the accuracy of the discrepancy profile. The standard error of measurement of the difference (sEM,,,) between assessment tools is often not known to testers, and frequently the information needed to calculate the SEM,,, (test reliability and intercorrelations among the tests) is not presented (McCauley and Swisher 1984). These criticisms of measurement ability raised for the areas of language and reading development are perhaps more serious for pediatric PT and OT service providers. These relatively new professional areas have fewer standardized instruments available for children (Campbell 1990), and in some cases the

reliability of the instruments is less than ideal (Ayres 1972, 1989). Cognitive referencing is used for prediction, identifying who should benefit from PT and OT services. Predictive models assume reasonable stability over time, so it is essential to know whether the cognitive/motor relationship, determined by current practices, does remain stable. If the cognitive/motor profile changes significantly from year to year in directions that would not be predicted by the cognitive referencing model (e.g. ‘flat’-profile children gaining motor skills to a greater degree than cognitive development), it would indicate that the conceptual model is flawed, or that our ability to measure the cognitive/motor relationship is inadequate. The purpose of this study was to examine the stability, over a two-year period, of the relationship between the cognitive and motor development of young children enrolled in a special education program. Specifically, we examined the relationship between the McCarthy Scales of Children’s Abilities (McCarthy 1972) General Cognitive Index (GCI) and the McCarthy Motor subscale. The McCarthy Motor Scale was selected to contrast with the McCarthy GCI because both measures were normed on the same population. The use of instruments normed on different populations is likely to reduce reliability between instruments (Salvia and Ysseldyke 1981). Therefore the use of the GCI and Motor Scale eliminates the possibility that reliability between the measures is negatively influenced by norming sample differences. T o evaluate the stability of the cognitive/motor performance relationship, we examined whether the relationship changed significantly over time, whether there were strong correlations between cognitive/motor profiles over time, and whether children stayed in the same category of service eligibility (based on the cognitive referencing model) over the two-year period.

Method Subjects Ninety-four children, aged between three and seven years, who were enrolled in a

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TABLE I Descriptive statistics at each test period (N=94)

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McCarthy GCI McCarthy Motor

Test I Mean (SD)

Test 2 Mean (SD)

Test 3 Mean (SD)

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75.7 (16.4) 76.6 (15.8)

77.3 (17.1) 72.7 (14.8)

74.9 (15.8) 74.2 (16.9)

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special education program for two consecutive years at a Northwestern United States university laboratory school participated in this study. All eligible children were included. The children’s mean age was 4.5 (SD 0.79) years. There were 63 boys and 31 girls. State eligibility guidelines are not categorical before age six, so children with various disabilities are eligible with the status of ‘developmentally delayed’. This classification includes children with deficits of at least 1 SD below the mean in two or more of the areas of cognitive, language, social, gross motor and fine motor development, or a 2 SD delay in one area. a

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composite score, referred to as the general cognitive index (GcI). The GCI has a mean of 100 and a standard deviation of 16. The McCarthy Motor scale is composed of a number of gross motor activities: ball-bouncing, imitative action activities and a series of balancing activities, including walking on a straight line, walking backwards, standing on one foot, skipping, bean-bag catch and toss, and design copying. The Motor Scale has a mean of 50 and a standard deviation of 10. In order to compare the relationship of the McCarthy Gc1 and the Motor Scale using a common mean and standard deviation, we converted the Motor Scale to a mean of 100 and a standard deviation of 16.

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Data from this study were gathered over

a four-year period, using assessment

Procedures

information collected during the first and second years that the child participated in a preschool program. Children between the ages of three and five years attended special education preschool classes for two hours a day, five days per week, over a 180-day school year. Each preschool class contained 12 children. Students aged six to seven years attended transitional kindergartenlprimary classes for 5 % hours a day. These classes contained 14 children. Each classroom was staffed by a head teacher and an assistant teacher, and by PT and OT staff, who each served four classrooms.

The test was first administered between October and December, and again between May and August (the school is open from October to August). The average time between the two administrations was approximately eight (range six to 10) months. The third test was done between May and August of the second year. Approximately four testers per year administered the batteries: they did not assess the same children twice in order to avoid preconceptions about expected performance. The relationship between cognitive ability and motor performance was determined by subtracting the Motor Scale score from the GCI: a child with a GcI of 100 and a Motor score of 85 would have a Gcr-Motor relationship of + 15; a child with a GCI of 50 and a Motor Scale score of 60 would have a Gcl-Motor relationship of - 10.

Measures McCarthy Scales of Children’s Abilities (McCarthy 1972), a test of children’s cognitive abilities from ages 2% to 8% years, is composed of five separate scales: verbal, perceptual-performance, quantitative, memory and motor. The verbal, perceptual-performance and quantitative scales are added together to give a

Results Table I summarizes the mean level of

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TABLE II Changes within tests between test periods (N-94)

Befween tesfs I and 2 Mean (SO) Mean absolute (SD) McCarthy GCI McCarthy Motor

+ 1.6 (12.5) -3.8 (12.0)*

9-5 (8-3) 9.6 (8-2)

Between tests 2 and 3 Mean (SD) Mean absolute (SO) - 2 . 4 (13.1) + 1.4 (14.8)

9.9 (7.9) 11.2 (9.7)

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Instability of the intelligence quotient-motor quotient relationship.

The authors evaluated the stability over one- and two-year periods of the relationship between a cognitive measure (McCarthy General Cognitive Index) ...
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