Questions and Answers
Question #10


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Questions and Answers

 

Question # 10

Are there any rules for the classification of children who exhibit NLD?


We have generated some rules for this purpose. The rules should be used only to determine whether a comprehensive neuropsychological evaluation would be worthwhile. These rules are not a substitute for a neuropsychological evaluation.

Classification rules derived for 9- to 15-year-old children (Pelletier, Ahmad, & Rourke, 2001). (Percentages of cases for which each feature/rule applied). A brief version of the classification principle (in bold) follows each rule.

Note:
It is crucial to bear in mind that the importance of the rules presented here lies in the principles, not in the specific tests that were chosen to represent these principles. These principles are, of course, derived from the characteristics of NLD (See NLD Content and Dynamics), and are consistent with the proposed ICD definition of NLD (See Question #3). A consideration of all of these dimensions should allow for the characterization of groups of persons with NLD for research purposes (See Question #42) and for determining the extent to which the syndrome of NLD is represented in the behavioural phenotypes of various types of neurological disease, disorder, and dysfunction (See NLD and Neurological Disease).

(1) Less than two errors on simple tactile perception and suppression vs. finger agnosia, finger dysgraphesthesia, and astereognosis composite greater than 1 SD below the mean (90.9%)
Simple tactile-perceptual skills are superior to complex tactile-perceptual skills.

(2) WRAT /WRAT -R standard score for Reading is at least 8 points greater than Arithmetic (85.7%)
Single-word reading is superior to mechanical arithmetic.

(3) Two of WISC/WISC- R Vocabulary, Similarities, and Information are highest of the Verbal scale (77.9%)
Straightforward and/or rote verbal skills are superior to those involving more complex processing (e.g., Comprehension).

(4) Two of WISC/WISC -R Block Design, Object Assembly, and Coding subtests are the lowest of the Performance scale (76.6%)
Complex visual-spatial-organizational skills and speeded eye-hand coordination are impaired.

(5) Target Test at least 1 SD below the mean (63.6 %)
Memory for visual sequences is impaired.

(6) Grip strength within one standard deviation of the mean or above vs. Grooved Pegboard Test greater than one standard deviation below the mean (63.6%)
Simple motor skills are superior to those involving complex eye-hand coordination, especially under speeded conditions.

(7) Tactual Performance Test Right, Left, and Both hand times become progressively worse vis-a-vis the norms (59.7%)
Complex tactile-perceptual and problem-solving skills under novel conditions are impaired.

(8) WISC/WISC -R VIQ > PIQ by at least 10 points (27.3%)
Verbal skills are superior to visual-spatial-organizational skills.

Notes
(a) It should be clear that there is some overlap in the tests that contribute to some of these rules.

(b) These rules are very much in need of refinement, even after the rather impressive results of our first concurrent validity study.

(c) The following criteria are currently under investigation:

         The first 5 features: Definite NLD
         7 or 8 of these features: Definite NLD
         5 or 6 of these features: Probable NLD
         3 or 4 of these features: Questionable NLD
         1 or 2 of these features: Low Probability of NLD



Classification rules derived for 7- and 8-year-old children (Drummond, Ahmad, & Rourke, 2005). (Percentages of cases for which each feature/rule applied). A brief version of the classification principle (in bold) follows each rule.

(1) Target Test at least 1 SD below the mean (90.0%)
Memory for visual sequences is impaired.

(2) Two of Wechsler Intelligence Scale for Children Block Design, Object Assembly, and Coding subtests are the lowest of the Performance scale (90.0%)
Complex visual-spatial-organizational skills and speeded eye-hand coordination are impaired.

(3) Two of Wechsler Intelligence Scale for Children Vocabulary, Similarities, and Information are the highest of the Verbal scale (80.0%)
Straightforward and/or rote verbal skills are superior to those involving more complex processing (e.g., Comprehension).

(4) Tactual Performance Test Right, Left, and Both hand times become progressively worse vis-a-vis the norms (77.8%)
Complex tactile-perceptual and problem-solving skills under novel conditions are impaired.

(5) Grip Strength within one standard deviation of the mean or above versus Grooved Pegboard Test greater than one standard deviation below the mean (70.0%)
Simple motor skills are superior to those involving complex eye-hand coordination, especially under speeded conditions.

(6) Wechsler Intelligence Scale for Children VIQ > PIQ by at least 10 points (70.0%)
Verbal skills are superior to visual-spatial-organizational skills.

(7) WRAT standard score for Reading is at least 8 points higher than Arithmetic (60.0%)
Single-word reading is superior to mechanical arithmetic.

(8) Less than two errors are made on simple tactile perception and suppression versus finger agnosia, finger dysgraphesthesia, and astereognosis composite greater than one standard deviation below the mean (10.0%)
Simple tactile-perceptual skills are superior to complex tactile-perceptual skills.

Particularly notable regarding this ranking of the rules/criteria is that criteria #1, 2, and 3 are evident 80-90% of the time. It would appear that dropping #8 as a criterion would, in all likelihood, have no appreciable effect on classification/diagnostic accuracy. The strict application of criteria #1 through 3 should result in very few false positives or false negatives.

Notes
(a) It should be clear that there is some overlap in the tests that contribute to some of these rules.

(b) These rules are very much in need of refinement, even after the rather impressive results of our first concurrent validity study.

(c) The following criteria are currently under investigation:

         The first 3 features: Definite NLD
         Two of the first 3 features and one of 4 or 5: Definite NLD
         Criteria 4, 5, 6, & 7: Probable NLD
         Only two of features 1 through 7: Questionable NLD
         None of features 1 through 7: Low Probability of NLD

Notes:

(1) The interested reader should consult the two articles cited for details regarding how these rules were generated.

(2) Classification rules for children with Basic Phonological Processing Disabilities (BPPD) were also generated in these studies.

(3) In the Drummond et al. (2005) study it was determined that none of the children classified as probable or definite NLD met criteria for classification of probable or definite BPPD. Also, none of the children classified as probable or definite BPPD met criteria for classification of probable or definite NLD. Thus, the specificity of the classification rules was, in this sense, perfect (100%).



References


Drummond, C. R., Ahmad, S. A., & Rourke, B. P. (2005). Rules for the classification of younger children with Nonverbal Learning Disabilities and Basic Phonological Processing Disabilities. Archives of Clinical Neuropsychology, 20, 171-182.

Pelletier, P. M., Ahmad, S. A., & Rourke, B. P. (2001). Classification rules for Basic Phonological Processing Disabilities and Nonverbal Learning Disabilities: Formulation and external validity. Child Neuropsychology, 7, 84-98.

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