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Article Excerpt
Abstract. Data from the 2001 National Household Education Survey were examined to estimate the prevalence of comorbid AD/HD and LD among school-aged children in the United States and assess how this comorbidity was associated with selected parent-reported behavioral and academic outcomes. The observed prevalence of comorbidity coincided with estimates in previous studies. Parents of children with comorbid AD/HD + LD were significantly more likely than parents of children with LD-only to be contacted by teachers about behavioral problems at school. Additionally, students with comorbid disorders were more likely than students with AD/HD-only to show impaired academic outcomes. However, when compared to children with AD/HD-only, children with comorbidity did not show significantly impaired behavioral outcomes; and when compared to children with LD-only, they did not show significantly impaired academic outcomes.
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Attention-deficit/hyperactivity disorder (AD/HD) is a neurobiological disorder characterized by a chronic pattern of inattention and/or hyperactivity-impulsivity. This behavior pattern is exhibited more frequently and is more serious in nature than behavior displayed by individuals at a comparable developmental level (American Psychiatric Association [APA], 2000).
Three subtypes of AD/HD have been identified: (a) AD/HD with a significant pattern of inattentiveness (AD/HD, predominantly inattentive type); (b) AD/HD with significant symptoms of both hyperactivity and impulsivity (AD/HD, predominantly hyperactive-impulsive type); and (c) AD/HD with significant symptoms of inattentiveness, hyperactivity, and impulsivity (AD/HD, combined type) (APA, 2000). AD/HD has been described as "one of the most important disorders that child and adolescent psychiatrists treat" (p. 978) because of its persistence, interference with typical development and functioning, and prevalence (Cantwell, 1996).
Children and adolescents with AD/HD experience tremendous difficulty in academic performance and achievement (APA, 2000; Barkley, 2006; Biederman, Newcorn, & Sprich, 1991; Hechtman et al., 2004). In addition, AD/HD is associated with difficulties or deficits in behavioral performance (APA, 2000; Miranda, Presentacion,& Soriano, 2002). Indeed, Barkley, one of the leading researchers on AD/HD has stated "evidence that behavioral disinhibition, or poor effortful regulation and inhibition of behavior, is in fact the hallmark of this disorder is so substantial that it can be considered fact" (2006, p. 81).
Recent estimates of the prevalence of AD/HD among school-aged children include 3-6% (DeVeaugh-Geiss et al., 2002), 3-5% (U.S. Department of Health and Human Services, 1999), 6.8% (U.S. Department of Health and Human Services-Centers for Disease Control and Prevention [DHHS-CDCP], 2002), and 7.5% (Leibson, Katusic, Barbaresi, Ransom, & O'Brien, 2001). These rates emphasize that AD/HD is a common disorder of childhood.
Another disorder that commonly occurs in children and adolescents is a learning disability (LD). As defined by the Individuals with Disabilities Education Improvement Act of 2004 (IDEA, 2004), the federal law governing special education and related services in the United States, a specific learning disability is:
a disorder in one or more of the basic psychological processes involved in understanding or in using language, spoken or written, which disorder may manifest itself in the imperfect ability to listen, think, speak, read, write, spell, or do mathematical calculations.
In general, reading is the most common problem among students with LD (Bell, McCallum, & Cox, 2003). Some students experience difficulties in only one academic area, such as written communication (Mayes, Calhoun, & Crowell, 2000) or math (Mazzocco, 2005). Most of these students, however, have difficulties that span the entire range of academic as well as social areas (C. R. Smith, 2004). Indeed, the defining characteristic of students with LD has come to be known as unexpected underachievement (D. D. Smith, 2004) or an unexpected failure to learn despite "adequate intelligence, schooling, and their parents' best attempts at nurturing" (C. R. Smith, 2004, p. 2).
Although there are large discrepancies in reported prevalence rates of LD from state to state (C. R. Smith, 2004), recent prevalence estimates include 4-6% (Learning Disabilities Association, n.d., para. 1), 7.7% (DHHS-CDCP, 2002), and 6.1% (U.S. Department of Education, National Center for Education Statistics, 2005). Of note is that of the students receiving special education in the United States, approximately half are identified as having an LD (U.S. Department of Education, National Center for Education Statistics).
Previous research has indicated that LD and AD/HD frequently coexist; that is, they are comorbid. Reported rates of LD among children with AD/HD have varied widely, including 20-25% (Pliszka, 2000), 10-90% (Biederman, Faraone, & Lapey, 1992; Carmichael et al., 1997), and 10-92% (Semrud-Clikeman et al., 1992). A range in the rates of AD/HD among children with LD has also been reported. For example, Carmichael et al. found that 41-80% of students with LD concurrently had AD/HD.
The variability in comorbidity rates of AD/HD and LD may be due largely to inconsistencies in definitions of LD. Thus, when more stringent standards for defining learning disability have been applied, more modest rates of LD have been found in children diagnosed with AD/HD. Using two stricter assessment methods, Semrud-Clikeman et al. (1992) found LD rates of 23% and 17%, respectively, among students who had attention deficit disorder and hyperactivity. More recent investigations have indicated that fewer than 10% of children with AD/HD have learning disabilities when strict LD criteria are applied (San Miguel, Forness, & Kavale, 1996).
In contrast to comorbidity rates within the population of children with AD/HD or LD, an additional statistic of interest concerns the rate of AD/HD and LD comorbidity among all school-aged children. Estimates of this nature are scarce in the literature; however, the DHHS-CDCP (2002) has reported that 3.5% of school-aged children have comorbid AD/HD and LD.
The effects of AD/HD or LD (considered individually) on academic outcomes are well documented. However, less work has been carried out on the effects of the two as comorbid disorders on such outcomes. Several studies have pointed to an additive or intensification effect on learning/academic variables when AD/HD and LD occur together, rather than in isolation. A number of these have noted the impact of AD/HD with regard to academic difficulties in students with comorbid AD/HD and LD. For example, Mayes and colleagues (2000) compared Wechsler Individual Achievement Test and IQ scores among children 8-16 years of age with AD/HD, LD, or a combination of the two disorders. Among children with LD, problems with learning were significantly greater among those who also had AD/HD than those who did not, suggesting that AD/HD intensified learning problems in children with LD. Similarly, Tirosh, Berger, Cohen-Ophir, Davidovitch, and Cohen (1998) noted that, based on teachers' reports, children with combined LD and AD/HD performed significantly poorer in many areas of academic achievement than students with LD alone. Further, with regard to academic grades, McNamara, Willoughby, Chalmers, and YLC-CURA (2005) found that students without LD reported higher grades than students with LD, who, in turn, reported higher grades than adolescents with AD/HD and LD.
The impact of LD on academic problems in students with comorbid AD/HD and LD has also been noted. Faraone, Biederman, Monuteaux, Doyle, and Seidman (2001)...
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