"Incidence" of spoken language disorders refers to the number of new cases identified in a specified time period. No reliable data on the incidence of spoken language disorders in children were located.
"Prevalence" of spoken language disorders refers to the number of people who are living with a spoken language disorder in a given time period. The variability in prevalence estimates below is attributed to differences in how language impairment is defined, the nature of the population studied, and variations in the methodological procedures used (Law, Boyle, Harris, Harkness, & Nye, 2000; Pinborough-Zimmerman et al., 2007).
In children 7 years old and younger in the United Kingdom the median prevalence of receptive language delay/disorder ranged from 2.63%-3.59%, expressive language delay/disorder ranged from 2.81%-16%, and combined receptive and expressive language delay/disorder ranged from 2.02%-3.01% (Law et al., 2000).
The prevalence of language impairment in Canadian kindergarten children was 8.04% overall, 8.37% for girls, and 8.17% for boys (Beitchman, Nair, Clegg, & Patel, 1986).
Among Canadian children 7 to 14 years old with psychiatric disorders, 40% were found to have a language impairment (Cohen, Barwick, Horodezky, Vallance, & Im, 1998). In the Northeastern region of the United States, about 40%-50% of children and adolescent speakers of Spanish and English who were referred for psychiatric services were found to have a language delay or impairment following testing in both languages (Toppelberg, Medrano, Morgens, & Nieto-Castañon, 2002).
The prevalence of SLI for kindergartners in the upper Midwestern region of the United States was 7.4% overall, 6% for girls, and 8% for boys (Tomblin et al., 1997). Prevalence of SLI in racial/ethnic groups was highest in Native Americans, with African Americans being the next highest, followed by Hispanics, and then Whites. No students of Asian descent presented with SLI (Tomblin et al., 1997); however, other research does indicate that SLI is present in children of Asian descent (Gray, 2003; Lahey & Edwards, 1999).