Mean Length of Utterance and Other Quantitative Measures of Spontaneous Speech in Russian-Speaking Children

Purpose 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 a rich system of grammatical and derivational morphemes. Method We collected audio recordings of spontaneous speech samples from 27 Russian-speaking children aged between 2;9 and 5;7 (years;months) over individual play sessions. For each participant, we transcribed the first 100 complete utterances and coded them for several types of utterance length measurements, including length in morphemes (grammatical and derivational), words, and syllables. At a sample level, we calculated the average number of produced unique grammatical forms, getting an alternative quantitative estimate of children's morphosyntactic abilities. Results 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. The average number of unique grammatical forms remains a sensitive measurement of language capabilities even in older children aged over 3;6. 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. Conclusions This article demonstrated that MLU can be used in young Russian-speaking children under 3;0-3;6. Also, we showed that the classical morpheme calculation approach can be substituted with counting syllables, which is more time efficient in the absence of automated parsers and is potentially more appropriate for some (e.g., polysynthetic) languages. Our 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.