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Journal of IntellectualDisability Research (JIDR).Volume 55, part 7, July 2011

Authors: C. L. Neece, B. L. Baker,

J. Blacher & K.A. Crnic.

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Introduction

Children and adolescents with intellectualdisability (ID) are at high risk for mentaldisorders.

Studies have indicated that children with IDare at heightened risk for attention-deficit/hyperactivity disorder (ADHD).However, what is still unclear is whether the

ADHD diagnosis has the same meaning inthe presence of ID as it does for typicallydeveloping children.

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Introduction

Some studies have argued that the apparentrisk for ADHD in children with ID is simplydue to their developmental delay, citingresearch showing that ADHD symptoms

(e.g. inattentiveness, overactive /impulsivebehaviour) are characteristic of individualswith low cognitive functioning (Reiss &Valenti-Hein 1994; Tonge et al. 1996;

Gjaerum & Bjornerem 2003).

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Introduction However, other studies provide support for

ADHD as a valid psychiatric diagnosis forchildren with ID. Handen et al. (1998)examined a sample of children with ID withand without elevated levels of ADHD

symptoms and found differences in terms ofactivity level and attention difficulties, evenafter controlling for intellectual functioning(Handen et al. 1998).

Fee et al. (1994) found no significantdifferences between children with ID andADHD and children with ADHD alone interms of their psychological characteristics

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Aim of the study

The current study expands on thesestudies investigating the validity ofADHD as a diagnosis for children with IDby comparing the developmental course of

ADHD in typically developing childrenand children with ID.

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Hypotheses There will not be any significant difference

in the presentation of ADHD (i.e.prevalence, sex difference, co-morbidityand symptom endorsement) between thetwo status groups.

There will not be any significant differencein the age of onset of ADHD (i.e. year offirst meeting diagnostic criteria) between

the two status groups.

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Hypotheses con There will not be any significant difference

in the stability of ADHD diagnosis amongthe two status groups.

There will not be any significant differencein terms of trajectories of inattentive andhyperactive/impulsive symptom acrossearly and middle childhood between thetwo status groups

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Methodology Participants

Participants were 228 families in alongitudinal study of young children, withsamples drawn from Southern California(78%) and Central Pennsylvania (22%).

The present sample was comprised of allfamilies for whom data were available onthe primary measures at child age 5 years.

Table 1 shows demographic characteristics.In the combined sample, there were moreboys (58.4%) than girls

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Methodology con

Procedures Procedures were approved by the

Institutional Review Boards of the threeuniversities. University of California, LosAngeles; University of California, Riverside;The Pennsylvania State University (Baker etal. 2003).

Children at age 5 and their mothers cameinto the child study centre. Research

assistants administered the Stanford-Binetto children while their mothers completeddemographic and diagnostic interviews.

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Methodology con Measures

1. Stanford-Binet IV (Thorndike et al. 1986)

2. Vineland Adaptive Behavior Scales

(Sparrow et al. 1984)3. Diagnostic Interview Schedule for Children

(Costello et al. 1985)

4. Teacher Report Form Ages 618

(Achenbach & Rescorla 2001).

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Results

Rates of ADHD were significantly higher inthe ID and borderline group compared tothe TD group at every time point, whilethere were no differences in the rates ofADHD between the ID and borderlinegroups. These differences are shown inTable 2.

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Results con

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Results con These differences are shown in Table 2 as

risk ratios. Because the ID and borderlinegroups did not differ on any demographicvariable or on prevalence of ADHDdiagnosis at any age, these two groups were

combined in subsequent analyses in order toincrease statistical power.

There were no significant differences inrates of ADHD diagnosis by child sex at any

age., however at age 6, the rates of ADHDwere marginally higher in boys than girls inthe TD group (X2 = 3.56, P = 0.06). Chi-squares ranged from 0.08 to 3.56 in the TDgroup and from 0.31 to 1.52 in the ID group.

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Results con The co-morbidity of ADHD and other

mental disorders in this sample wasconsistently higher in the ID group. At ages5, 6, 7 and 8, the per cent of TD groupchildren who met criteria for ADHD and

one or more additional disorders was 7.1%,4.2%, 7.7% and 3.5%.

Symptom presentation for ADHD wassimilar among children with TD and ID

across time. The present analyses showedthis finding to be consistent at ages 6, 7 and8; at no time point did the ID and TD groupsdiffer significantly in number of symptomsendorsed.

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Resultscon A Spearmans rank correlation coefficient on

the endorsement frequency between items forthe TD and ID samples was moderately highat age 5 (r = 0.64,P < 0.001), age 6 (r = 0.58,P