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How Many Children with Autism Spectrum Disorder Are Functionally Nonverbal?

Thursday, 2 May 2013: 15:00
Meeting Room 1-2 (Kursaal Centre)
P. Mirenda1, I. M. Smith2, J. Volden3, P. Szatmari4, S. E. Bryson5, E. Fombonne6, W. Roberts7, T. Vaillancourt8, C. Waddell9, L. Zwaigenbaum10, S. Georgiades4, E. Duku4 and A. Thompson4, (1)University of British Columbia, Vancouver, BC, Canada, (2)Dalhousie University / IWK Health Centre, Halifax, NS, Canada, (3)University of Alberta, Edmonton, AB, Canada, (4)Offord Centre for Child Studies & McMaster University, Hamilton, ON, Canada, (5)Dalhousie University/IWK Health Centre, Halifax, NS, Canada, (6)Montreal Children's Hospital, Montreal, QC, Canada, (7)University of Toronto, Toronto, ON, Canada, (8)University of Ottawa, Ottawa, ON, Canada, (9)Simon Fraser University, Burnaby, BC, Canada, (10)Glenrose Rehabilitation Hospital, University of Alberta, Edmonton, AB, Canada
Background:  Historical estimates are that 50% of children with autism over the age of 6 are nonverbal (Lord & Rutter, 1994), meaning that they have few or no words or that they do not speak as their primary method of communication.  However, in 2004, Lord, Risi, and Pickles provided data from the United States suggesting that approximately 14%-20% of children with autism remain nonverbal by age 9. These estimates may be biased, however, by the non-systematic sampling procedures.

Objectives: The purpose of this study was to estimate the proportion of children with ASD in Canada who remain nonverbal at the time of school entry, using a systematic sampling procedure and the same measurement criteria as Lord et al. (2004). 

Methods: Data were drawn from the Pathways in ASD study and included 231 children from five Canadian provinces. At first assessment, within 4 months of diagnosis, the children’s mean age was 40 months (range = 24-61 mo). The ADOS module and question 30 (overall level of language) on the ADI-R were used to define four language categories, as per Lord et al. (2004). These were:  (a) fluent language; (b) phrases but not fluent (daily uses phrases ≥ 3 words which sometimes include a verb, and are comprehensible to others); (c) words but not 3-word phrases; and (d) no consistent speech (i.e., “nonverbal,” defined as fewer than 5 words total or speech not used daily). The proportions of children in each language category were calculated separately for ages 2-2:11, 3-3:11, and 4-4:11 at the time of diagnosis (T1) and at the time of school entry (T2, ages 6-7).

Results: Of the total sample at T1, 1.7%  had fluent speech, 25.5% had phrases, 36.1% had words but no phrases, and 36.7% were nonverbal. At T2 (age 6-7), 54% had fluent speech, 24.2% had phrases, 12.1% had words but no phrases, and only 9.8% were nonverbal. A strong relationship was found between verbal level at T2 and age at T1. Of the 89 children diagnosed between ages 2-2:11, who were most comparable to those in the Lord et al. (2004) study, 20.1% remained nonverbal at ages 6-7 and 54.4% had fluent speech. Corresponding figures for 89 children diagnosed between ages 3-3:11 were 5.2% and 52.6%, and for 53 children diagnosed between ages 4-4:11 were 2% and 56%. All children in the nonverbal group, regardless of age of diagnosis, had cognitive age-equivalent scores ≤ 21 months at T1 and scored ≤ 29 months at T2.

Conclusions: In this sample, the proportion of Canadian children with ASD who were diagnosed at age 2 and who remained nonverbal after age 6 was similar to results reported by Lord et al. (2004). Overall, in our sample, approximately 10% of the children remained nonverbal by school entry. The children who remained nonverbal, regardless of the age of diagnosis, were those whose low mental ages at T1 remained relatively stable at T2.

See more of: Language Development
See more of: Core Deficits
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