Differentiating normal variability from inconsistency in children's speech: normative data

Background: In young, typically developing children, some word production variability is expected, but highly inconsistent speech is considered a clinical marker for disorder. Speech-language pathologists need to identify variability versus inconsistency, yet these terms are not clearly differentiated. Not only is it important to identify inconsistency, but also it needs to be defined and measured so that clinical decisions are evidence based. In order to understand inconsistent speech production, typical variability must be described. Aims: This paper differentiates between variability and inconsistent productions. Variability is defined as productions that differ, but can be attributed to factors described in normal acquisition and use of speech. Inconsistency is speech characterized by a high proportion of differing repeated productions with multiple error types, both segmental (phoneme) and structural errors (consonant-vowel sequence within a syllable). The study describes and quantifies the consistency of word production in typically developing children aged between 3;0 and 6;11 years. Methods and Procedures: This paper reports a large cross-sectional study (n=409) of the consistency of children's production of words within the same linguistic context. Outcomes and Results: The study found that the speech of typically developing children is highly consistent. Children in the youngest age group demonstrated the highest levels of variability, but it remained below 13% with 10% reflecting maturational influences. Conclusions: Inconsistent production cannot be considered a typical feature of speech development. The results inform differential diagnosis of speech disorder.