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.
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.
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).
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.