Mean Length of Utterance and Other Quantitative Measures of Spontaneous Speech in Russian-Speaking Children
This study investigated methodological and theoretical aspects of using mean length of utterance (MLU) and its alternatives in cross-linguistic research, and in particular its applicability to Russian – a language with opaque grammatical paradigms and rich system of derivational morphology.
Audio recordings of spontaneous speech samples were collected from 27 Russian-speaking children aged between 2;9 and 5;7 (years;months) over individual play sessions. For each participant, the first 100 complete utterances were transcribed and coded for several types of utterance length measurements, including their length in morphemes (grammatical and derivational), words and syllables. In addition, the average number of unique grammatical forms produced by each child was calculated.
A combination of Pearson correlation analysis and Bland-Altman difference plots established that MLU can be reliably used in Russian-speaking children aged around 3;0 years. In contrast, the average number of unique grammatical forms remains a sensitive measurement of language capabilities even in older children aged over 3;6. In addition, it was demonstrated that two quantitative measurements – MLU in syllables and morphemes – show good agreement, suggesting that these measurements can be used interchangeably across studies. Sample size analysis revealed that samples under 75 utterances do not provide sufficient reliability for estimating a child’s MLU.
This paper demonstrated that MLU can be used in young Russian-speaking children under 3;0–3;6 years. Also, we showed that the classical morpheme calculation approach can be substituted with counting syllables, which is much more time-efficient in the absence of automated parsers and is potentially more appropriate for some (e.g., polysynthetic) languages. Importantly, the proposed alternative to MLU – the average number of grammatical forms in a sample – appears to be a more sensitive measurement of language capabilities even in older children. Theoretical and practical implications of these findings are discussed.