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The proportion of children with autism who qualify as ‘minimally verbal’ depends on the criteria researchers use to identify them. The findings suggest that some characteristics of minimally verbal children, including nonverbal intelligence quotient (IQ) and ability to function in everyday life, vary accordingly.
“I think it’s important for researchers to be clear about what their definition is, what that means for the group composition, and make sure that’s appropriate for the questions that they’re asking,” says Charlotte DiStefano, who presented the findings 10 May at the 2018 International Society for Autism Research annual meeting in Rotterdam, the Netherlands. DiStefano is a clinical instructor in psychiatry and biobehavioral sciences at the University of California, Los Angeles.
DiStefano and her colleagues analyzed data on the speech of 1,478 children, aged 5 to 18, from the Autism Genetic Resource Exchange, a repository of data from people with autism and their family members. The data include results from autism diagnostic evaluations and parent responses to questions about their child’s speech and other skills.
Using these data, the researchers compared five strategies for classifying children as minimally verbal. Two of the strategies classify children as minimally verbal if they speak single words or no words during an evaluation for autism, using either of two standard diagnostic tests. In the third strategy, a child is flagged as minimally verbal if a clinician assessed her using the ‘module 1’ version of one of these tests, the Autism Diagnostic Observation Schedule (ADOS). (This version is reserved for children who speak few or no words.)
The remaining two methods rely on word use as reported by parents. One classifies children as minimally verbal if they have language abilities that are roughly equivalent to those of an 18-month-old — meaning they rely primarily on gestures or single words to communicate. The other puts children in this category if they have language abilities equivalent to those of a 24-month-old (meaning they can speak some words).
A total of 30 percent of the children met criteria for being minimally verbal under all the definitions. This finding is in line with previous results.
Using the ADOS module method, 28 percent of the children in the sample are minimally verbal. Of all the children classified as minimally verbal, these children have the highest average nonverbal IQ, and the highest score on a measure of adaptive behavior, which is the ability to function in daily life.
Using the 18-month-old equivalence method, only 13 percent of the children are minimally verbal.
The other three methods classify 20 to 21 percent of the children as minimally verbal. These three groups of children have similar average IQs and adaptive behavior scores; these scores fall in between those of children who qualify as minimally verbal using the other two methods.
There were no age or sex differences among the children flagged under each definition.
As a whole, the children had a wide range of nonverbal IQ scores, reinforcing the notion that the number of words a person can speak has little to do with her cognitive ability.
DiStefano says she recommends researchers use one of the ADOS methods. “Because ADOS is a direct assessment of the child, I think going with an ADOS definition is probably best,” she says.
But the ADOS is time-consuming. Using the 24-month-old equivalence method is a reasonable and quicker alternative, she says.
For more reports from the 2018 International Society for Autism Research annual meeting, please click here.