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A note on the distinction between attention deficit disorder and reading disability: Are there group-specific cognitive deficits?
BRAIN
AND
LANGUAGE
34,
350-352 (1988)
NOTES AND DISCUSSION A Note on the Distinction between Attention Deficit Disorder and Reading Disability: Are There Group-Specific Cognitive Deficits? DAVID
L. SHARE AND STEVEN SCHWARTZ University
of Queensland
In a recent paper in this journal, Felton and her colleagues (R. H. Felton, F. B. Wood, I. B. Brown, S. K. Campbell, & M. R. Harter, 1987, Brain and Language, 31, 171-184) claim to have demonstrated that children suffering from attention deficit disorder have different cognitive deficits from children with reading disorders. In this paper, we show that the two groups were inappropriately compared and that Felton et al.‘s own data do not support their conclusions. 0 1988 Academic
Press, Inc.
Although the authors of the DSM-ZZZ(American Psychiatric Association, 1980) consider attention deficit disorder (ADD) to be distinct from developmental reading disability (RD), the two often appear to go together (Douglas & Peters, 1979; Levine, Busch, & Aufsuser, 1982). Attempts to separate the two syndromes have been plagued by methodological and definitional problems (inconsistent diagnostic criteria, a failure to control for differences in verbal intelligence and inappropriate experimental tasks). It has also become clear that the best way to identify cognitive deficits specific to RD or ADD is to compare the two groups on several different tasks. Differential performance-an ADD group deficit on one task and an RD group deficit on another-constitutes evidence that the disorders are distinct. A study using this “multiple comparison” approach was reported in this journal by Felton, Wood, Brown, Campbell, and Harter (1987). While other studies have reported multiple comparisons between similar groups This paper was prepared with the support of the Australian Research Grant Scheme, the British Red Cross Society, and the NHMRC. Requests for reprints should be sent to Steven Schwartz, Department of Psychology, University of Queensland, St. Lucia, Queensland 4067. Australia. 350 0093-934X/88 $3.00 Copyright All rights
0 1988 by Academic Press, Inc. of reproduction in any form reserved.
NOTES AND DISCUSSION
351
on measures of sustained and selective attention (see Tarnowski, Prinz, & Nay, 1986, for example), Felton et al. concentrated on measures of memory and naming. They concluded that ADD and RD are characterized by different cognitive deficits. Specifically, “deficits in learning and memory for recently acquired information occur as a function of ADD rather than RD while deficits in naming are specific to RD rather than ADD” (p. 171). We believe that this conclusion is unwarranted; indeed, we will show that it contradicts Felton et al.‘s own results. We first wish to make clear, that our criticism is not directed toward Felton et al.‘s hypothesis or their experimental procedures. The care with which they selected their groups and their measures, and the clarity of their presentation could serve as a model for other researchers in the area.] Our main concern is the logic underlying their data analysis. Felton et al. organized their data into a 2 x 2 structure in which RD and ADD (present or absent) were the two independent variables. Eleven dependent variables representing scores on the various tasks were analyzed in a multivariate analysis in which age and intelligence were (quite appropriately) covariates. The outcome of this analysis was a main effect for both independent variables but no interaction. A set of follow-up univariate analyses were performed to isolate the dependent variables responsible for the main effects. These univariate analyses were performed comparing the ADD children to the non-ADD children and comparing the RD children to the non-RD children. Felton et al. found little overlap among the dependent measures responsible for the two main effects. Most of the RD differences were found on tasks requiring naming (of letters, objects, digits and so on). In contrast, the ADD vs. non-ADD differences were on tests of memory and on measures of semantic and linguistic fluency. These findings formed the basis for their conclusions as quoted above. These conclusions were not justified, however, because the main effects they reported only showed that, when two of the three disordered groups were pooled (either ADD-RD and ADD or RD and ADD-RD) the combined group differed from the remaining children who were mainly normal controls. With the inclusion of normal controls in the comparison, these results are hardly surprising. To conclude that ADD and RD children are differentfrom one another, it is necessary to compare the two disordered groups directly. Fortunately, the necessary means and standard deviations are given in Felton et al.‘s Table 2 (p. 180). Columns 2 and 3 contain the scores of the “pure” ADD group and the “pure” RD group, respectively. We compared these two groups on each of the dependent measures using a series of small sample t tests. Using the same statistical criterion as Felton et al. 0, < .Ol), only two of the 13 tests were statistically ’ Although we should note that 24% of their unselected group of non-reading-disordered children were diagnosed as ADD, an extraordinarily high number.
352
NOTES AND DISCUSSION
significant. These were Rapid Naming of Objects and the Boston Naming Test. On both tests the ADD group was superior. No other comparisons differentiated the ADD and RD groups. Thus, there is no evidence in these data to support Felton et al.‘s conclusion that ADD children have learning and memory deficits not present among RD children and there is only weak evidence that RD children have naming deficits not found in ADD children. We characterize this latter evidence as weak not only because only two tests reached statistical significance but also because three other naming tasks failed to distinguish between the two groups. Moreover, the differences between the two groups could easily have been the result of factors other than RD and ADD. For example, the ADD children had substantially higher intelligence scores than the RD children. If the influence of intelligence had been removed from our t tests, the few differences we did observe may well have disappeared. Even if many group differences had been obtained, this would still not constitute unequivocal evidence for group-specific cognitive deficits because the various measures used by Felton et al. have not been equated for reliability and discriminating power. Chapman and Chapman (1973) have shown that when two measures differ in difficulty or reliability, it is possible to find group by test interactions purely for psychometric reasons alone. A minimum requirement for demonstrating group-specific cognitive deficits, therefore, is that the various dependent measures are all equally reliable and not subject to ceiling, regression, or any other artifact that would produce spurious interactions. We conclude, along with Rutter (1983), that there is no evidence demonstrating a distinct ADD disorder. REFERENCES American Psychiatric Association 1980.Diagnostic and statistical manual of mental disorders. Washington, DC: Author. 3rd ed. Chapman, L. J., & Chapman, J. P. 1973. Problems in the measurement of cognitive deficit. Psychological Bulletin, 79, 380-385. Felton, R. H., Wood, F. B., Brown, 1. B., Campbell, S. K., & Harter, M. R. 1987. Separate verbal memory and naming deficits in attention deficit disorder and reading disability. Brain and Language, 31, 171-184. Douglas, V. I., & Peters, K. G. 1979. Toward a clearer definition of the attentional deficit disorder of hyperactive children. In G. A. Hale & M. Lewis (Eds.), Attention and cognitive development. New York: Plenum Press. Pp. 173-247. Levine, M. D., Busch, B., & Aufsuser, C. 1982. The dimension of inattention among children with school problems. Pediatrics, 70, 387-395. Rutter, M. 1983. Behavioral studies: Questions and findings on the concept of a distinctive syndrome. In M. Rutter (Ed.), Developmental neuropsychiatry. New York: Guilford Press. Pp. 259-279. Tarnowski, K. J., Prinz, R. J., & Nay, S. M. 1986. Comparative analysis of attentional deficits in hyperactive and learning disabled children. Journal ofAbnormal Psychology, 95, 341-345.
AND
LANGUAGE
34,
350-352 (1988)
NOTES AND DISCUSSION A Note on the Distinction between Attention Deficit Disorder and Reading Disability: Are There Group-Specific Cognitive Deficits? DAVID
L. SHARE AND STEVEN SCHWARTZ University
of Queensland
In a recent paper in this journal, Felton and her colleagues (R. H. Felton, F. B. Wood, I. B. Brown, S. K. Campbell, & M. R. Harter, 1987, Brain and Language, 31, 171-184) claim to have demonstrated that children suffering from attention deficit disorder have different cognitive deficits from children with reading disorders. In this paper, we show that the two groups were inappropriately compared and that Felton et al.‘s own data do not support their conclusions. 0 1988 Academic
Press, Inc.
Although the authors of the DSM-ZZZ(American Psychiatric Association, 1980) consider attention deficit disorder (ADD) to be distinct from developmental reading disability (RD), the two often appear to go together (Douglas & Peters, 1979; Levine, Busch, & Aufsuser, 1982). Attempts to separate the two syndromes have been plagued by methodological and definitional problems (inconsistent diagnostic criteria, a failure to control for differences in verbal intelligence and inappropriate experimental tasks). It has also become clear that the best way to identify cognitive deficits specific to RD or ADD is to compare the two groups on several different tasks. Differential performance-an ADD group deficit on one task and an RD group deficit on another-constitutes evidence that the disorders are distinct. A study using this “multiple comparison” approach was reported in this journal by Felton, Wood, Brown, Campbell, and Harter (1987). While other studies have reported multiple comparisons between similar groups This paper was prepared with the support of the Australian Research Grant Scheme, the British Red Cross Society, and the NHMRC. Requests for reprints should be sent to Steven Schwartz, Department of Psychology, University of Queensland, St. Lucia, Queensland 4067. Australia. 350 0093-934X/88 $3.00 Copyright All rights
0 1988 by Academic Press, Inc. of reproduction in any form reserved.
NOTES AND DISCUSSION
351
on measures of sustained and selective attention (see Tarnowski, Prinz, & Nay, 1986, for example), Felton et al. concentrated on measures of memory and naming. They concluded that ADD and RD are characterized by different cognitive deficits. Specifically, “deficits in learning and memory for recently acquired information occur as a function of ADD rather than RD while deficits in naming are specific to RD rather than ADD” (p. 171). We believe that this conclusion is unwarranted; indeed, we will show that it contradicts Felton et al.‘s own results. We first wish to make clear, that our criticism is not directed toward Felton et al.‘s hypothesis or their experimental procedures. The care with which they selected their groups and their measures, and the clarity of their presentation could serve as a model for other researchers in the area.] Our main concern is the logic underlying their data analysis. Felton et al. organized their data into a 2 x 2 structure in which RD and ADD (present or absent) were the two independent variables. Eleven dependent variables representing scores on the various tasks were analyzed in a multivariate analysis in which age and intelligence were (quite appropriately) covariates. The outcome of this analysis was a main effect for both independent variables but no interaction. A set of follow-up univariate analyses were performed to isolate the dependent variables responsible for the main effects. These univariate analyses were performed comparing the ADD children to the non-ADD children and comparing the RD children to the non-RD children. Felton et al. found little overlap among the dependent measures responsible for the two main effects. Most of the RD differences were found on tasks requiring naming (of letters, objects, digits and so on). In contrast, the ADD vs. non-ADD differences were on tests of memory and on measures of semantic and linguistic fluency. These findings formed the basis for their conclusions as quoted above. These conclusions were not justified, however, because the main effects they reported only showed that, when two of the three disordered groups were pooled (either ADD-RD and ADD or RD and ADD-RD) the combined group differed from the remaining children who were mainly normal controls. With the inclusion of normal controls in the comparison, these results are hardly surprising. To conclude that ADD and RD children are differentfrom one another, it is necessary to compare the two disordered groups directly. Fortunately, the necessary means and standard deviations are given in Felton et al.‘s Table 2 (p. 180). Columns 2 and 3 contain the scores of the “pure” ADD group and the “pure” RD group, respectively. We compared these two groups on each of the dependent measures using a series of small sample t tests. Using the same statistical criterion as Felton et al. 0, < .Ol), only two of the 13 tests were statistically ’ Although we should note that 24% of their unselected group of non-reading-disordered children were diagnosed as ADD, an extraordinarily high number.
352
NOTES AND DISCUSSION
significant. These were Rapid Naming of Objects and the Boston Naming Test. On both tests the ADD group was superior. No other comparisons differentiated the ADD and RD groups. Thus, there is no evidence in these data to support Felton et al.‘s conclusion that ADD children have learning and memory deficits not present among RD children and there is only weak evidence that RD children have naming deficits not found in ADD children. We characterize this latter evidence as weak not only because only two tests reached statistical significance but also because three other naming tasks failed to distinguish between the two groups. Moreover, the differences between the two groups could easily have been the result of factors other than RD and ADD. For example, the ADD children had substantially higher intelligence scores than the RD children. If the influence of intelligence had been removed from our t tests, the few differences we did observe may well have disappeared. Even if many group differences had been obtained, this would still not constitute unequivocal evidence for group-specific cognitive deficits because the various measures used by Felton et al. have not been equated for reliability and discriminating power. Chapman and Chapman (1973) have shown that when two measures differ in difficulty or reliability, it is possible to find group by test interactions purely for psychometric reasons alone. A minimum requirement for demonstrating group-specific cognitive deficits, therefore, is that the various dependent measures are all equally reliable and not subject to ceiling, regression, or any other artifact that would produce spurious interactions. We conclude, along with Rutter (1983), that there is no evidence demonstrating a distinct ADD disorder. REFERENCES American Psychiatric Association 1980.Diagnostic and statistical manual of mental disorders. Washington, DC: Author. 3rd ed. Chapman, L. J., & Chapman, J. P. 1973. Problems in the measurement of cognitive deficit. Psychological Bulletin, 79, 380-385. Felton, R. H., Wood, F. B., Brown, 1. B., Campbell, S. K., & Harter, M. R. 1987. Separate verbal memory and naming deficits in attention deficit disorder and reading disability. Brain and Language, 31, 171-184. Douglas, V. I., & Peters, K. G. 1979. Toward a clearer definition of the attentional deficit disorder of hyperactive children. In G. A. Hale & M. Lewis (Eds.), Attention and cognitive development. New York: Plenum Press. Pp. 173-247. Levine, M. D., Busch, B., & Aufsuser, C. 1982. The dimension of inattention among children with school problems. Pediatrics, 70, 387-395. Rutter, M. 1983. Behavioral studies: Questions and findings on the concept of a distinctive syndrome. In M. Rutter (Ed.), Developmental neuropsychiatry. New York: Guilford Press. Pp. 259-279. Tarnowski, K. J., Prinz, R. J., & Nay, S. M. 1986. Comparative analysis of attentional deficits in hyperactive and learning disabled children. Journal ofAbnormal Psychology, 95, 341-345.