Speech sound disorder at 4 years: prevalence, comorbidities, and predictors in a community cohort of children

Aim: The epidemiology of preschool speech sound disorder is poorly understood. Our aims were to determine: the prevalence of idiopathic speech sound disorder; the comorbidity of speech sound disorder with language and pre-literacy difficulties; and the factors contributing to speech outcome at 4 years. Method: One thousand four hundred and ninety-four participants from an Australian longitudinal cohort completed speech, language, and pre-literacy assessments at 4 years. Prevalence of speech sound disorder (SSD) was defined by standard score performance of ≤79 on a speech assessment. Logistic regression examined predictors of SSD within four domains: child and family; parent-reported speech; cognitive-linguistic; and parent-reported motor skills. Results: At 4 years the prevalence of speech disorder in an Australian cohort was 3.4%. Comorbidity with SSD was 40.8% for language disorder and 20.8% for poor pre-literacy skills. Sex, maternal vocabulary, socio-economic status, and family history of speech and language difficulties predicted SSD, as did 2-year speech, language, and motor skills. Together these variables provided good discrimination of SSD (area under the curve=0.78). Interpretation: This is the first epidemiological study to demonstrate prevalence of SSD at 4 years of age that was consistent with previous clinical studies. Early detection of SSD at 4 years should focus on family variables and speech, language, and motor skills measured at 2 years. What this paper adds: First longitudinal and prospective study of 4-year-olds to detect 3.4% prevalence of speech disorder in a community cohort. Comorbidity of speech sound disorder (SSD) and language disorder was 40.8% and 20.8% for poor pre-literacy skills. The proportion of males (54%) with SSD and comorbid language disorder was double that of females (28%). Detection of SSD by 4 years should focus on speech, language, and motor abilities at 2 years.