ADHD and Prevalence of LDs

8/3/2019 ADHD and Prevalence of LDs

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THE EFFECT OF COM ORBID A D /H D AN DLEARNING DISABILITIES ON PARENT REPORTED

BEHAVIORAL AND ACADEMIC OUTCOMESOF CHILDREN

Thomas / . Smith and Gail Adams

Abstract Data from the 2001 National Household EducationSurvey were examined to estimate the prevalence of comorbidAD/HD and LD among school-aged children in the United Statesand assess how this comorbidity was associated with selectedparent-reported behavioral and academic outcomes. The observedprevalence of comorbidity coincided with estimates in previousstudies. Parents of children with comorbid AD/HD -i- LD were sig-nificantly more likely th an parents of children w ith LD-only to becontacted by teachers about behavioral problems at school.Additionally, students with comorbid disorders were more likelythan students with AD/HD-only to show impaired academic out-comes. However, when compared to children with AD/HD-only,children with comorbidity did not show significantly impairedbehavioral outcomes; and when compared to children with LD-only, they did n ot show significantly impaired academ ic outcomes.

THOMAS ]. SMITH, Northern Illinois University, DeKalb.GAIL ADAMS, Northern Illinois University, DeKalb.

Attention-deficit/hyperactivity disorder (AD/HD) is aneurobiological disorder characterized by a chronicpattern of inattention and/or hyperactivity-impulsiv-ity. This behavior pattern is exhibited more frequentlyand is more serious in nature than behavior displayedby 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/HDwith significant symptoms of both hyperactivityand impulsivity (AD/HD, predominantly hyperactive-

impulsive type); and (c) AD/HD with significantsymptoms of inattentiveness, hyperactivity, and im-pulsivity (AD/HD, combined type) (APA, 2000). AD/HDhas been described as "one of the most importantdisorders that child and adolescent psychiatrists treat"(p. 978) because of its persistence, interference withtypical development and functioning, and prevalence(Cantwell, 1996).Ghildren and adolescents with AD/HD experiencetremendous difficulty in academic performance andachievement (APA, 2000; Barkley, 2006; Biederman,Newcorn, & Sprich, 1991; Hechtman et al., 2004), In

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addition, AD/HD is associated with difficulties ordeficits in behavioral performance (APA, 2000; Miranda,Presentacion, & Soriano, 2002). Indeed, Barkley, on e ofthe leading researchers on AD/HD has stated "evidencetha t behavioral disin hibition, or poor effortful regula-tion and inhibition of behavior, is in fact the hallmarkof this disorder is so substantial th at it can be consideredfact" (2006, p. 81).Recent estimates of the prevalence of AD/HD amongschool-aged children include 3-6% (DeVeaugh-Geisset al., 2002), 3-5% (U.S. Department of Health andHuman Services, 1999), 6.8% (U.S. Department ofHealth and Human Services-Centers for Disease Gontroland Prevention [DHHS-CDCP], 2002), and 7.5%(Leibson, Katusic, Barbaresi, Ransom, & O'Brien, 20 01).These rates emphasize that AD/HD is a common disor-der of childhood.Another disorder that commonly occurs in childrenand adolescents is a learning disability (LD). As defined

by the Individuals with Disabilities Education Improve-ment Act of 2004 (IDEA, 2004), the federal law govern-ing special education and related services in the UnitedStates, a specific learning disability is:a disorder in one or more of the basic psychologi-cal processes involved in understanding or in usinglanguage, spoken or written, which disorder maymanifest itself in the imperfect ability to listen,think, speak, read, write, spell, or do mathematicalcalculations.In general, reading is the most common problemamong students with LD (Bell, McCallum, & Cox,2003). Some studen ts experience difficulties in on ly on eacademic area, such as written communication (Mayes,Calhoun, & Crowell, 2000) or math (Mazzocco, 2005).Most of these students, however, have difficulties thatspan the entire range of academic as well as social areas(C. R. Smith, 2004). Indeed, the defining characteristicof students with LD has come to be known as unex-pected underachievement (D. D. Smith, 2004) or anunexpected failure to learn despite "adequate intelli-gence, schooling, and their parents' best attempts atnurturing" (C. R. Smith, 2004, p, 2).Although there are large discrepancies in reportedprevalence 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 ofEducation, National Center for Education Statistics,2005). Of note is that of the students receiving specialeducation in the United States, approximately halfare identified as having an LD (U.S. Department ofEducation, N ational Center for Education Statistics),Previous research has indicated that LD and AD/HDfrequently coexist; that is, they are comorbid. Reported

rates of LD among children with AD/HD have variedwidely, including 20-25% (Pliszka, 2000), 10-90%(Biederman, Faraone, & Lapey, 1992; Carm ichael et al.,1997), and 10-92% (Semrud-Clikeman et al,, 1992). Arange in the rates of AD/HD among children with LDhas also been reported. For example, Carmichael et al,found that 41-80% of students with LD concurrentlyhad AD/HD,The variability in como rbidity rates of AD/HD and LDmay be due largely to inconsistencies in definitions ofLD. Thus, when more stringent standards for defininglearning disability have been applied, more modestrates of LD have been found in children diagnosed withAD/HD. Using two stricter assessment methods,Semrud-Clikeman et al. (1992) found LD rates of 23%and 17%, respectively, among students who h ad atten-tion deficit disorder and hyperactivity. More recentinvestigations have indicated tha t fewer than 10% ofchildren with AD/HD have learning disabilities whenstrict LD criteria are applied (San Miguel, Forness, &Kavale, 1996).

In contrast to comorbidity rates within the popula-tion of children w ith AD/HD or LD, an ad ditional sta-tistic of interest concerns the rate of AD/HD andLD comorbidity among al l school-aged children.Estimates of this nature are scarce in the literature;however, the DHHS-CDCP (2002) has reported that3.5% of school-aged children have comorbid AD/HDand 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 twoas comorbid disorders on such outcomes. Several stud-ies have po inted to an a dditive or intensification effecton learning/academic variables when AD/HD and LDoccur together, rather th an in isolation. A number ofthese have noted the impact of AD/HD with regard toacademic difficulties in students with comorbid AD/HDand LD. For example, Mayes and colleagues (2000)compared Wechsler Individual Achievement Test andIQ scores among children 8-16 years of age withAD/HD, LD, or a combination of the two disorders.Among children with LD, problems with learning weresignificantly greater among those who also had AD/HDthan those who did not, suggesting that AD/HD inten-sified learning problems in children with LD. Similarly,Tirosh, Berger, Cohen-Ophir, Davidovitch, and Cohen(1998) noted that, based on teachers' reports, childrenwith co mbine d LD and AD/HD performed significantlypoorer in many areas of academic achievement thanstudents with LD alone. Further, with regard to aca-demic grades, McNamara, Willoughby, Chalmers, andYLC-CURA (2005) found that students without LDreported higher grades than students with LD, who, in

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turn, reported higher grades than adolescents withAD/HD a nd LD.The impact of LD on academic problems in studentswith comorbid AD/HD and LD has also been noted.Faraone, Biederman, Monuteaux, Doyle, and Seidman(2001) found that the presence of LD among boys 6-17years of age who had AD/HD predicted poorer achieve-ment scores at four-year followup than for boys withAD/HD alone. The authors stated that their results"show th at, a lthoug h ADHD itself is a risk factor for aca-demic difficulties, these deficits are more severe inADHD youth with c oncom itant LD" (p. 227). Studentswith both disorders exhibited significantly higher ratesof grade repetition, remedial tutoring, and placement inspecial classes than their peers with AD/HD only.

The need for increased special education servicesamong students with comorbid AD/HD and LD has alsobeen addressed by others. Summarizing the results ofseveral emp irical inv estigations, San M iguel et al. (1996)concluded that when AD/HD (or another disorder) iscomorbid with LD, it appears that there is an increasedneed for special education support. Moreover, theDHHS-CDCP (2002) reported that among children withcomo rbid AD/HD and LD, 64.7% were receiving specialeducation services compared to 45.9% of children withLD alone, and 11.7% of children with AD/HD-only.

AD/HD alone has been more closely associated withbehavioral difficulties than LD-only. In a study of chil-dren with ADHD, ADD, emotional disturbance (ED), orLD, Palomares (1991) found that children with ED andthose with ADHD/ADD exhibited the most deviantbehavior. In a study of students with ADD withouthyperactivity (ADD/WO), ADD with hyperactivity(ADD/H), or LD, Stanford and Hynd (1994) found gen-eral support for their hypothesis that the behavior ofchildren in the ADD/WO group was more similar to th ebehavior of children in the LD group. However, theyalso found that students in bo th ADD subtypes exhib-ited behavioral symptoms that were not displayed tothe sarne degree by students with LD.

W ith regard to the com bined effect of AD/HD and LDon behavioral outcomes, findings closely parallel thoserelated to academic outcomes: Data generally supportan additive or intensification effect when AD/HD andLD occur together, rather than in isolation. Severalresearchers have investigated the impact of AD/HDwithregard to behavioral difficulties in studen ts with comor-bid AD/HD and LD. Flicek (1992), for example, foundthat among boys in second through sixth grade, thosewith AD/HD and LD were reported (via peer nomina-tions and ratings) to be more disruptive and to startmore fights than boys with LD alone. Flicek also notedthat teachers rated students with com orbid AD/HD andLD as exhibiting significantly more difficulties with

cooperation, self-control, and oppositional/defiantbehavior than students with LD only. Similarly, Tiroshet al. (1998) found tha t teacher ratings of several behav-ioral outcomes in students with comorbid AD/HD andLD were significantly lower than in students with LDalone. One of the psychosocial variables McNamara etal. (2005) studied among adolescents with and withoutvarious disorders (LD-only, AD/HD and LD, neither dis-order) was temp eram ent (i.e., activity level, distractibil-ity, sleep/rhythmicity, affect/mood, persistence, andapp roach). Although no statistically significant differ-ences were found among disorder groups, adolescentswith comorbid AD/HD and LD reported a higher levelof negative characteristics in all temperament areasthan adolescents with LD-only.

There is a paucity of literature on the im pact of LD onbehavioral difficulties amon g studen ts with comorbidAD/HD and LD. In one of the existing studies, Pisecco,Baker, Silva, and Brooke (2001) compared 11-year-oldboys with both AD/HD and reading disabilities (RD) toboys with AD/HD or RD alone. Results showed thatboys who currently showed symptoms of comorbidAD/HD and RD had displayed significantly more diffi-culty with behavioral control at a younger age (ages 3and 5) than boys with RD alone. The authors alsoreported that comorbidity was associated with morebehavioral control problems than AD/HD-only.

The implications of comorbidity for school-basedassessments and interventions have also been exam-ined. Marshall and Hynd (1997), for example, discussedscreening students with AD/HD for certain learning dis-abilities and monitoring students with attention prob-lems (particularly those without hyperactivity) forpotential problems with math performance. In a reviewof the relationship between AD/HD and reading disabil-ities, Riccio and Jemison (1998) suggested that becauseADHD and RD frequently co-occur, children who arereferred for either condition should be assessed for theother condition as well. They recommended that assess-ments of children referred for potential ADHD be com-prehensive enough either to rule out or to identify aco-occurring reading disability. They further suggestedthat assessments of children who are referred for diffi-culties in early reading skills be sufficiently com prehen -sive to include an assessment of behavioral domains.Moreover, Riccio and Jemison supported the notionthat concurrent interventions that address language,academic, and behavioral concerns are necessary forchildren with AD/HD and RD.

Much of the previous research on this topic has beenconducted with students from clinical populations,including referrals to diagnostic clinics as well as psy-chiatric and pediatric settings (e.g., Faraone et al., 2002;Mayes et al., 2000; Tirosh et al., 1998). It is possible that



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children referred to specialty clinics comprise a selectgroup of children, and do not necessarily represent thepopulation of children with AD/HD and/or LD at large(Tirosh et al., 1998). A community sample provides fora potentially more diverse population of children thanclinical samples (whose members typically include chil-dren with more severe AD/HD or LD symptoms), andtherefore might allow for broader generalization.Further, community samples (e.g., DHHS-CDCP,2002) often make use of parent reports about the dis-ability status of a child. While some studies have castdoubt on the efficacy of parent reports (e.g., Antrop,Roeyers, Oosterlaan, & Van Oost, 2002; Mitsis, McKay,Schulz, Newcorn, & Halperin, 2000), others havesupported their accuracy (e.g., Biederman, Faraone,Mo nuteaux, & Grossbard, 2004). However, in the sestudies, parents were asked to report the presence orabsence of symptoms of a particular disorder, whereascommunity surveys typically query parents about thepresence or absence of the disorder itself- a distinct issueand one likely influenced by information parentsreceive from professionals in regular contact with theirchild. As such, parents' ability to remember informationconcerning the disorder status of their child may be apertinent issue here. In a study examining parental abil-ity to remember medical information about their child,Pless and Pless (1995) found that a high level of agree-ment existed between maternal reports of serious healthconditions exhibited by children and correspondingmedical record information.

According to the DHHS-CDCP (2002), few studieshave examined the accuracy of parental reports of diag-nosed learning and behavioral disorders in children.The DHHS-CDCP postulated, however, that parentreports about diagnosed LD and ADD may be preferredover school or medical record information, because "aparent may be the one informant who can describefindings from evaluations by health care providers andschool personnel and also provide detailed informationabout a child's sociodemographic characteristics" (p. 8).Similarly, parental reports about their children's aca-demic performance have been found to match substan-tially teacher reports on the same child (Schaefer &Edgerton, 1980) and to have equal predictive validity asadolescent-reported grades (Schuerger & Kuna, 1987),which are frequently used in studies of adolescents.

The present study was designed to (a) estimate theprevalence of comorbid AD/HD and LD among school-aged children in the United States using a large, nation-ally representative com mun ity sample; and (b) examinethe impact of this comorbidity on a set of behavioraland academic outcome variables. Based on the cited lit-erature, we hypothesized that (a) children with comor-bid AD/HD and LD or AD/HD-only would show a

greater incidence of behavioral problems than childrenwith LD-only, (b) children with comorbid AD/HD andLD or LD only would show a greater incidence of aca-demic problems than children with AD/HD-only, and(c) comorbidity of AD/HD and LD would show anintensification of adverse academic outcomes whencompared to LD-only. Investigation of the effects ofcomorbidity on these outcomes is important, becausethe results may be used to inform school-based behav-ioral and academic interventions.

METHODSInstrumentation and DataThe present study made use of the 2001 NationalHousehold Education Survey (NHES), developed bythe National Center for Educational Statistics (NCES,2003a, 2003b). Specifically, we used Volume III ofthe data set, which contains responses from a parent orhead of household (hereafter "parent") of 9,583school-aged children aged 5-15 attending kindergartenthrough grade eight in the United States. Participantswere contacted by pho ne via random-digit dialing fromJanuary 2 through April 14, 2001, and computer-assisted interviews were administered. The survey wasadministered with the primary goal of obtaining infor-mation, regarding relative a nd non-relative care ofchildren during non-school hours, in addition to par-ticipation in before- and after-school programs, activi-ties, and self-care. The surveyed households includedfamilies with children attending public and privateschools, as well as families with home-schooled chil-dren. The sampling scheme was designed to provide agood representation of civilian households in theUnited States and to provide "reliable national esti-mate s" (NCES, 2003a, p . 5).

For the purposes of the present study, we consideredresponses from parents of children currently attendingpublic or private schools. Specifically, responses to thefollowing survey questions were examined: (a) "Does(child) have a specific learning disability?" (yes/no); (b)"Does (child) have attention deficit disorder, ADD, orADHD?" (yes/no); (c) "Overall, across all subjects he/shetakes at schoo l, does he /she get mo stly (A's, B's, C's, D's,F's)?"; (d) "Have any of (child's) teachers or his/herschool contacted you (or child's mother, stepmother,foster mother, father, stepfather, foster father, grand-mother, grandfather, aunt, uncle, cousin, or the otheradults in your household) about any behavior problemshe/she is having in school this year?" (yes/no); (e)"Have any of (child's) teachers or his/her school con-tacted you (or child's mother, stepmother, fostermother, father, stepfather, foster father, grandmother,grandfather, aunt, uncle, cousin, or the other adults inyour household) about any problems he/she is having

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with school work this year?" (yes/no); (f) "During thisschool year, has (child) had an out-of-school suspensionor been expelled from school?" (yes/no); and (g) "Sincestarting kindergarten, has child repeated anygrades/kindergarten?" (yes/no). For the grade repetitionvariable, we recoded the responses to reflect the pres-ence or absence of grade repetition within three gradelevel ranges (K-3, 4-6, 7-8).Finally, we were interested in whether the target childwas receiving special education services under theIndividuals with Disabilities Education Act. Therefore,we considered parental responses to the survey question"Is (child) receiving services for his/her disability/dis-abilities thro ug h an Individualized (Family Service Plan,or IFSP/Educational Program, or IEP)?"Although it was not possible to fully ensure the accu-racy of the parent responses used in the present study,several aspects of the survey may have helped toincrease accuracy. First, th e queries a bout AD/HD statusand behavioral and academic outcomes of the childrenwere embedded within the context of a comprehensiveand in-depth set of survey questions, enhancing theprospect that respondents would develop some level ofcomfort and trust with the interviewer. Second, the datawere collected in a manner that ensured participantanonymity. Third, data were based on parent reports ofchildren currently attending school (rather than retro-spective reports), thereby reducing inaccuracies thatcould result from parental lapses in memory.Procedure

To estimate the prevalence of AD/HD and LD comor-bidity, we analyzed data from all 9,583 children in the

data set and computed the relative frequency of eachdisorder: comorbid AD/HD and LD (AD/HD H- LD),AD/HD with no LD (AD/HD-only), and LD with noAD/HD (LD only), along with standard errors and asso-ciated confidence intervals. Additionally, the preva-lence of LD among children with AD/HD, as well as theprevalence of AD/HD among children with LD, was esti-mated by constructing a 2 x 2 cross-classification table(AD/HD status by LD status), and computing the per-centages of children in each of the categories.

To determine how a child's parent-reported AD/HDand/or LD status was related to the categorical behav-ioral and academic outcome variables, we considereddata from the children in the data set (H = 1,167) with adisorder (i.e., comorbid AD/HD + LD, AD/HD-only, an dLD-only), and computed the frequency and percentageof students within each disorder category showing"undesirable" academic or behavioral outcomes, alongwith standard errors and 95% confidence intervals.Significance was determined by comparing theseintervals for the groups of interest (with lack of overlapindicating significance, a = .05 level). Effect sizes (thephi coefficient, which indicates degree of associationbetween a pair of binary variables) were computed toassess the magnitude of the effect when pairs of disor-ders were assessed on each outcome. To reduce intra-household dependencies in the data, a single, randomlyselected case (child) was selected from each household,resulting in a working sample of = 970.

RESULTSPrevalence of Comorbid AD/HD + LDTo address the occurrence of comorbid AD/HD + LD,

Table 1Frequency and Percentage

Disorder StatusAD/HD + LDAD/HD-onlyLD-onlyNeither AD/HD n or LDTotal

of Children

n35 834 346 68416

9583

Within Each Disorder

Percent3.73.64.987.8

100.0Note. Standard errors have been adjusted by the root design effect (DEFT).

Category

StandardError0.25

0.250.290.43

95% ConfidenceInterval

(3.21, 4.19)(3.12, 4.08)(4.34, 5.46)(86.95, 88.65)

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Table 2Cross-Classification

AD/HDNo AD/HDTotal

of AD/HD Status With LD Status

LD35846 6824

NoLD34 3

8,4168,759

Total82 4

8,8829,583

we considered the sample and computed the frequencyand percentage of children with each disorder. Table 1shows the distribution of children by disorder status.Out of the total number of children (n = 9,583), 358(3.7%) had comorbid AD/HD + LD, 343 (3.6%) hadAD/HD-only, and 466 (4.9%) had LD-only.We also estimated the relative occurrence of comor-bid LD among children with AD/HD, as well as theoccurrence of comorbid AD/HD among children withLD. Table 2 shows the cross-classification of all ch ildrenin the data set by disorder status. Of the 824 childrenwho were reported by parents as having AD/HD, 358(43.4%) were indicated to have a comorbid learningdisability. Among th e 701 children w ith a learning dis-ability, 51.1% were reported by their parents as havingcomorbid AD/HD.Effect of Comorbid AD /HD + LD on BehavioralOutcomesThe next research question concerned the effect ofthe various disorders on behavioral and academic out-comes. Table 3 shows the percentage of children withineach disorder category whose parents were contactedby teachers regarding behavioral problems, along withstandard errors and 95% confidence intervals for thesepercentages. Based on a comparison of the confidenceintervals (specifically, examining for lack of overlap),parents of children with AD/HD + LD and childrenwith AD/HD only were significantly more likely to becontacted by the teacher for child behavioral problemsthan parents of children with LD-only. A weak-to-mod-erate effect size ((j) = .26) was evident for this difference.However, no significant difference existed betweenchildren with comorbid AD/HD + LD and children withAD/HD-only, and a small effect size was observed ((j) =.07). When we used suspension/expulsion as thebehavioral outcome, no significant differences were

evident among any of the three disorder categories (seeTable 3). Further, small effect sizes resulted when chil-dren with comorbid AD/HD + LD were compared tochildren with AD/HD only ((() = .03) and children withLD only (()> = .10) on this question.Effect of Comorbid AD/HD + LD on AcademicOutcomesIn a similar manner, we compared children fromeach of the three disorder categories on three academicoutcome variables. Table 4 shows the percentage ofchildren within each disorder category whose parentswere contacted regarding problems with school work.As illustrated, p arents of children with comorbidAD/HD + LD were significantly more likely to be con-tacted th an parents of children with AD /HD-only. Asimilar pattern emerged when we considered the aca-demic outcomes "child received average grades of 'Cor lower" and grade repetition, with pa rents of childrenwith comorbid AD/HD + LD reporting significantlylower grades and more grade repetition th an parents ofchildren with AD/HD-only. Effect sizes indicated thatthe magnitude of the proportional difference in theseacademic outcomes was small (with all values < .22).Additionally, for two of the three academic outcomes(grades of 'C or lower and grade repetition), a signifi-cant {p < .05) difference was apparent between childrenwith LD only and children with AD/HD only.However, no significant difference was apparent forany of the three academic variables when childrenwith comorbid AD/HD + LD were compared to chil-dren with LD-only.

In sum, it appeared that the presence of comorbidAD/HD + LD exerted an additive effect over thepresence of AD/HD-only on academic outcomes, butexerted no intensification effect over LD-only.



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Table 3Frequency and Percentage of Children WithinBehavioral Outcomes

DisorderAD/HD + LDAD/HD-onlyLD-only


Each Disorder Status Category With Specific

Teacher Contacted Parents Regarding Behavioral Problemsn

15 112396

n473934

Percent50.743.925.5

Standard Error2.902.972.25

Child Suspended or ExpelledPercent15.8

13.99.0


95% ConfidenceInterval(44.99, 56.35)(38.12, 49.74)(21.12, 29.94)


Table 4Frequency and Percentage of Children Within Each Disorder Status Category With SpecificAcademic Outcomes




Teacher Contacted Parents Regarding School Workn179125188

Percent60.044.650.0


Child Received Average Grades of C or Lowern11683

139

n8731109

Percent52.335.649.3Child Repeated

Percent29.211.830.9


a GradeStandard Error3.72

2.183.44



95% ConfidenceInterval(21.57, 35.86)(6.84, 14.99)

(22.14, 34.78)



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Table 5Frequency andServices

DisorderAD/HD + LDAD/HD o nlyLD o nly

Percentage

n158

64216

of Children Within

Percent55.426.671.5

Each Disorder Category Receiving IFSP/IEP



Interaction EffectsAs a followup analysis, we examined how ethnicity,gender, and student grade level interacted with childdisorder status to affect the behavioral and academicoutcomes. Logit modeling, a technique used to examineassociations among two or more categorical variables(see DeMaris, 1992), was used for this analysis. Resultsindicated no significant (p > .05) interactive effects forethnicity or gender, except for the outcome of graderepetition. For this outcome, a significant disorder-status X ethnicity interaction was evident (Ax^ [df= 4]= 10.23, p < .05). Specifically, White children withAD/HD-only or with LD-only were least likely to haverepeated a grade, followed by Hispanic children, thenBlack children. This differed from the pattern of graderepetition for child ren w ith com orbid AD/HD + LD,where Hispanic children were least likely to haverepeated a grade, followed by White children, thenBlack children .Reception oflESP/IEP ServicesAs an additional followup analysis, we investigatedwhether reception of IFSP/IEP services differed by dis-order status. To assess this, we computed the propor-tion of children within each of the three disordercategories whose parents reported that they werereceiving IFSP/IEP services (see Table 5). When wecompared the confidence intervals for these propor-tions, all three disorder categories differed from oneanother. Specifically, children with LD were mostlikely to receive services, followed by children withcomorbid AD/HD + LD, and children with AD/HDonly. Followup logit analyses showed no significant(p > .05) gender X disorder, ethnicity X disorder, orgrade level X disorder interaction effects on receptionof services.

DISCUSSIONThe purpose of this study was to (a) estimate theprevalence of parent-reported comorbid AD/HD + LDamong school-aged children in the United States and(b) examine the impact of this comorbidity on selectedbehavioral and academic outcome variables. Whenprevalence was examined, the results indicated that3.7% of the children were reported by a parent to havecomorbid AD/HD + LD. This figure is strikingly similarto the 3.5% prevalence rate reported in the DHHS-CDCP summary (2002) of the 1997-98 National HealthInterview Survey data. Of note is that the DHHS-CDCPsurvey, like the National Household Education Surveyused in the present study, involved a nationally repre-sentative household sample. In the DHHS-CDCP sur-vey, information on sociodemographic characteristicsof sample children living in the households wasobtained by interviewing an adult family member, ofwhom over 90% were parents. In the present study,93.2% of respondents were parents. The reported ratesof AD/HD only and LD only (3.6% and 4.9%, respec-tively) were also very similar to th e estimates reported inthe DHHS-CDCP study (3.3% for AD/HD only and 4.2%for LD only).

Results of the present study also showed that amongchildren who were reported by parents as havingAD/HD, 43.4% had comorbid LD; among children withLD, 51.1% were reported as having comorbid AD/HD.Although these values appear to be in the midrange ofthe wide span of estimates reported in the literature, the43.4% figure is higher than the estimated rate of LDamong children with AD/HD when "strict" definitionsof LD have been used (e.g., San Miguel et al., 1996;Semrud-Clikeman et al., 1992), suggesting that parentsin this study may have used less stringent definitions ofLD when responding to the survey query.

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Behavioral OutcomesThis study also examined the effects of the variousdisorder categories on behavioral outcomes. Withregard to the first behavioral outcome, teacher contact-ing parents regarding child behavior problems, resultsindicate that such contact was significantly greater forstudents with comorbid AD/HD + LD than for studentswith LD-only, supporting the findings of earlier researchby Flicek (1992), Tirosh et al. (1998), McNamara et al.(2005), and Pisecco et al. (2001). In add ition, our resultsindicate that parents of children with AD/HD-onlywere contacted significantly more frequently regardingbehavioral problems than parents of children with LD-only.Although no significant differences were foundamong disorder categories with regard to the secondbehavioral outcome, suspension and expulsion, theobserved sample statistics for children with comorbid-ity were more adverse than for children with LD-only.Hence, our first hypothesis, that children with parent-reported comorbid AD/HD + LD or AD/HD-only wouldshow a greater incidence of behavioral problems thanchildren with LD-only, was partially supported.The impact of AD/HD on behavioral outcomes seenin the present study is not surprising, given currentperspectives on this disorder. Alluding to deficientrule-governed behavior as a primary deficit or an asso-ciated condition in children with AD/HD, Barkleynoted that:these children [are] described as not listening, fail-ing to initiate compliance to instructions, beingunable to maintain compliance to an instructionover time, and b eing poor at adhering to directionsassociated with a task. All these descriptors areproblems in the regulation and inhibition ofbehavior, especially by rules. (2006, p. 133)Academic OutcomesThe results of this investigation indicate that for allthree academic variables, comorbidity led to signifi-cantly poorer outcomes than the presence of AD/HDalone . These findings supp ort earlier work by Faraone etal . (2001), who found that AD/HD + LD had moreadverse effects on academic outcomes than the presenceof AD/HD-only. Furthermore, for two of the three aca-demic variables (grades lower than C and grade repeti-tion), students with LD-only performed worse thantheir counterparts with AD/HD-only. Hence, our thirdhypo thesis, tha t children with com orbid AD/HD + LDor LD-only would show a greater incidence of academicproblems than children with AD/HD-only, was gener-ally upheld. Taken together, these results point to theimportant contribution of the presence of a learningdisability to academ ic variables, lendin g further support

to the phenomenon of unexpected underachievementassociated w ith learn ing disabilities.The results of this investigation also indicate that forall three academic outcomes examined (teacher contactregarding school work, C grades or lower, and grade rep-etition), comorbid AD/HD + LD did not exert a signifi-cantly greater negative impact over the presence of LD-only. These findings do not support previous research(Mayes et al., 2000; McNamara et al., 2005; Tirosh et al.,1998), which suggested an additive or intensificationeffect on learning an d academ ic variables when AD/HDand LD occur together compared to LD-only. Hence,our third hypothesis, that comorbidity would result inan intensification of adverse academic outcomes com-pared to LD in isolation, was not supported.Several explanations for th e differences between thesefindings and those of previous studies may be posited.First, it has been noted that academic deficits tend to bemost pronounced in children with the subtype ofAD/HD without hyperactivity (predominantly inatten-tive type) (Marshall & Hynd, 1997) or in children withsubtypes of AD/HD characterized by inattention (pre-dominantly inattentive type and combined type) (APA,200P). One possibility is that students with the pre-dominantly inattentive and/or combined type ofAD/HD were underrepresented in the current study.This cannot be determined, however, because the sur-vey data do no t distinguish among the various AD/HDsubtypes. A second possible explanation is tha t t heseverity level of learning disabilities repo rted by parentsof the students in the LD-only group was greater thanthat of the learning disabilities reported by the parentsof students with AD/HD + LD.Interaction effectsThe present study also found no significant interac-tion effects of ethnicity, gender, or grade level withchild disorder status on the parent-reported academicand behavioral outcomes (with the exception of graderepetition). That is, differences in these outcomesamong disorder categories did not vary by ethnicity,gender, or grade, suggesting tha t th e effects of these dis-orders remain fairly constant across these demographiccharacteristics.Reception oflFSP/IEP ServicesOur results, like those of the DHHS-CDCP study(2002), show that significantly fewer students withAD/HD-only received special education services thanstuden ts w ith com orbid disorders or LD-only. A verylikely explanation for this finding is that many studentswith AD/HD receive modifications and accommoda-tions under Section 504 of the Rehabilitation Act of1973 (a U.S. civil rights law that prohibits discrimina-tion against individuals with disabilities) rather than



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IDEA (Friend & Bursuck, 2006). Students served underSection 504 do not have IFSPs or IEPs, and thus wouldnot have heen considered in the current study.Previous research has also shown that students withcomorhid AD/HD + LD receive services at higher ratesthan students with LD alone (DHHS-CDCP, 2002). Bycontrast, our results indicate that children with LD-onlyand children with comorbid AD/HD + LD did no t differsignificantly in this respect, suggesting that AD/HDadded little to this outcome. These results would lendsupport to the previous suggestion that the severitylevel of the learning disabilities reported hy parents ofthe students in the LD-only group was greater than thatof the learning disahilities reported hy the parents ofstudents with AD/HD + LD.The results related to the reception of IFSP/IEP serv-ices yielded another notahle finding. That is, data fromthe DHHS-CDCP (2002) survey (collected in 1997-98)showed that only 12% of students with AD/HDreceived special education services. Our data (collectedin 2001) indicate that 26.6% of students with AD/HDwere receiving special education services, representingmore than a twofold increase in special education serv-ices in only a few years. Historically, children withAD/HD were not eligible to receive special educationservices under IDEA, unless they also met criteria forone of the other major disability categories withinIDEA; for example, a learning disahiiity (DuPaul,Eckert, & McGoey, 1997). However, when IDEA wasreauthorized in 1997, AD/HD was included as a specificexample of the "Other Health Impaired" disability cat-egory. It is possible that as parents have hecomeincreasingly aware of this change, they have advocatedfor special education and related services on the hasisof an AD/HD diagnosis alone.LimitationsAlthough other studies have examined AD/HD + LDcomorhidity issues, few have investigated this topicusing large nationally representative samples. Thestudy conducted by the DHHS-CDCP (2002) examinedthe impact of comorhid AD/HD + LD on the use ofhealth care services and other health conditions usingsuch a sample. The only school-related variablereported in the DHHS-CDC study, however, was theuse of special education services. The present studyextends this work hy examining how additional behav-ioral and educational outcomes (teacher contactregarding behavioral prohlems, suspension/expulsion,teacher contact regarding school work, grades of C orlower, and grade repetition) are related to AD/HD + LDcomorhidity.As this study is the first of its kind to examine theimpact of comorbid AD/HD + LD on specific behavioral

and academic variables using a large, national, house-hold sample, we consider these findings to he prelimi-nary. Hence, future research should he conductedto confirm or refute the results. Also, a limited set ofparent-reported behavioral and academic outcomes wasused in this study. In addition, the study relied on par-ent reports of disorder status, and although there is evi-dence to support the validity of such reports, this maystill be viewed as a limitation inherent in this type ofstudy. Moreover, the survey question pertaining to thepresence of ADD or AD/HD did not discriminate am ongthe different suhtypes of AD/HD. Future research m ightexamine a broader array of behavioral and academicoutcomes, use a variety of reporting sources, andinclude data on different suhtypes of AD/HD.Implications for PracticeAs previously indicated, Riccio and Jemison (1997)recommended that assessments of children who arereferred for potential AD/HD he comprehensive enoughto rule out or identify a potential reading disahiiity. In asimilar fashion, these authors suggested that assess-ments of children referred for early reading difficultiesbe broad enough to include an assessment of hehavioraldomains. The substantial levels of comorbidity foundboth in this study and in previous research support thisrecommendation; that is, a diagnosis of one disordershould alert school personnel to the possibility that theother disorder is also present. Hence, when a child isdiagnosed w ith a learning disahiiity, for example, it maybe wise to screen for AD/HD; the presence of AD/HDmay herald behavioral difficulties for which specificinterventions are warranted. Similarly, when a childpresents with AD/HD, the possibility of an LD should beconsidered; a learning disability ma y be associated w ithincreased academic problems that require specializedinterventions. Faraone et al. (2001), whose researchfound that although AD/HD alone is a risk factor foracademic difficulties, these problems are even moresevere in youth with AD/HD who have coexisting LD,suggested "the need to develop appropriate screeningtechniques to identify ADHD children with comorbidLD who likely require more extensive psychoeduca-tional interventio ns" (p. 228). In sum, the presence of comorbid AD/HD + LD, compared to either disorder inisolation, may have important ramifications for inform-ing school-based behavioral and academic assessmentand intervention.

REFERENCESAmerican Psychiatric A ssociation. (2000). Diagnostic an d statisticalmanual of mental disorders (4th ed., Text Revision). Washington,DC: Author.Antrop, L, Roeyers, H., Oosterlaan, J., & Van Oost, P. (2002).Agreement between parent and teacher ratings of disruptive



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Smith, D. D. (2004). Introduction to special education: Teaching in anage of opportunity. Boston: Allyn and Bacon.Stanford, L. D., & Hynd, G. W. (1994). Congruence of behavioralsymptomatology in children with ADD/H, ADD/WO, and learn-ing disabilities. Joumal of Leaming Disabilities, 27(4), 243-253.Tirosh, E., Berger, J., Cohe n-Ophir, M., Davidovitch, M., & Coh en,A. (1998). Learning disabilities with andwithout attention-deficit hyperactivity disorder: Parents' and teachers' perspec-tives. Joumal of Child Neurology, 13(6), 270-276.U.S. Department of Education, National Center for EducationStatistics. (2005). Th e condition ofeducation 2005 (PublicationNo. NCES 2005-094). Washington, DC: U.S. GovernmentPrinting Office.

U.S. Department of Health and Human Services. (1999). Mentalhealth: A report of the Surgeon General. Retrieved Ju ne 9, 2005from http://www.surgeongeneral.gov/library/reports.htmU.S. Depar tment of Health and Human Services-Centers forDisease Control and Prevention (2002). Attention deficit disorderan d leaming disability: United States, 1997-98 (DHHS PublicationNo. (PHS) 2002-1534). Hyattsville, MD: Author.

Please address correspondence to: Thomas J. Sm ith, Dept. of ETRA,College of Education, Northern Illinois University, DeKalb, IL60115; [email protected]

DISSERTATION RESEARCH SCHOLARSHIPSThe Donald D. Hammill Foundation is awarding up to fivescholarships to assist students w ho require financial aid incomp leting their dissertations. Prerequisites for applicationare as follows:

The study must pertain tocharacteristics, services, orissues related to disabhngconditions.The student's doctoralcommittee must have approvedthe dissertation p roposal.

The student should haveplans to complete the studyduring the 2006-2007academic year.The amount requestedcannot exceed $5,000.

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8700 Shoal Creek BoulevardAustin, Texas 78757-6897512/451-0784 fax 512/[email protected]

Contact Cindy Thigpen at the address shown. The deadlinefor receiving completed applications is June 1, 2006; awardswill becom e available with the 2 006-2007 academic year.Money can be used for living expenses, materials, data collec-tion, tuition, clerical services, or other germa ne p urpose s.Preference is given to applicants who have a disability or whoare experiencing serious financial distress.



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Documents

ADHD and Prevalence of LDs