Inattention and hyperactivity/impulsivity among children with attention-deficit/hyperactivity-disorder, autism spectrum disorder, and intellectual disability.
Lower IQ tames parent-reported ADHD severity, so factor intelligence into every differential.
01Research in Context
What this study did
McClain et al. (2017) compared ADHD symptom levels across kids with six different diagnosis mixes. The groups were ADHD alone, ASD alone, ID alone, ASD plus ADHD, ID plus ADHD, and the triple combo of ASD plus ID plus ADHD.
Parents filled out the standard ADHD rating scale. The team then asked: who shows the most inattention and hyperactivity once we factor in IQ?
What they found
Children who had both ID and ADHD showed noticeably milder ADHD symptoms than children with ADHD alone. The same softening showed up for kids who had ASD plus ID plus ADHD.
In short, lower IQ was linked to lower reported ADHD severity, even when ADHD was present.
How this fits with other research
Matson et al. (2011) found ADHD is three times more common in kids with ID and lasts longer. Brunson agrees but adds a twist: once IQ is counted, the actual symptom intensity is lower.
Tonizzi et al. (2022) pooled data showing that ASD plus ADHD means worse executive control than ASD alone. Brunson does not contradict this; they simply show that raw hyperactivity scores drop when ID is also in the picture.
Bigham et al. (2013) warned that parent ratings can over-tag ADHD in kids with ID. Brunson’s IQ-linked pattern supports that warning—scores need an IQ lens before you trust them.
Why it matters
If you test a child with ID who also has ADHD, expect softer rating-scale numbers. Do not let the mild score talk you out of help the child may still need. Always note IQ, use developmental age, and pair rating scales with direct observation. This guards both against over-diagnosis in mild ID and under-diagnosis in bright kids with ASD.
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02At a glance
03Original abstract
BACKGROUND: Attention-Deficit/Hyperactivity Disorder (ADHD), Autism Spectrum Disorder (ASD), and Intellectual Disability (ID) are common co-occurring neurodevelopmental disorders; however, limited research exists regarding the presentation and severity of overlapping symptomology, particularly inattention and hyperactivity/impulsivity, when a child is diagnosed with one of more of these neurodevelopmental disorders. AIMS: As difficulties with inattention and hyperactivity/impulsivity are symptoms frequently associated with these disorders, the current study aims to determine the differences in the severity of inattention and hyperactivity/impulsivity in children diagnosed with ADHD, ASD, ID, and co-occurring diagnosis of ADHD/ID, ASD/ADHD, and ASD/ID. METHODS AND PROCEDURES: Participants in the current study included 113 children between the ages of 6 and 11 who were diagnosed with ADHD, ASD, ID, ADHD/ID, ASD/ADHD, or ASD/ID. Two MANOVA analyses were used to compare these groups witih respsect to symptom (i.e., inattention, hyperactivity/impulsivity) severity. OUTCOMES AND RESULTS: Results indicated that the majority of diagnostic groups experienced elevated levels of both inattention and hyperactivity/impulsivity. However, results yielded differences in inattention and hyperactivity/impulsivity severity. In addition, differences in measure sensitivity across behavioral instruments was found. CONCLUSIONS AND IMPLICATIONS: Children with neurodevelopmental disorders often exhibit inattention and hyperactivity/impulsivity, particularly those with ADHD, ASD, ASD/ADHD, and ADHD/ID; therefore, differential diagnosis may be complicated due to similarities in ADHD symptom severity. However, intellectual abilities may be an important consideration for practitioners in the differential diagnosis process as children with ID and ASD/ID exhibited significantly less inattention and hyperactive/impulsive behaviors. Additionally, the use of multiple behavior rating measures in conjunction with other assessment procedures may help practitioners determine the most appropriate diagnosis.
Research in developmental disabilities, 2017 · doi:10.1016/j.ridd.2017.09.009