Mean Length of Utterance in Czech Toddlers: Validity Estimates and Comparison of Words, Morphemes, and Syllables

What is it about?

Mean length of the utterance (MLU) is a well-established measure of language acquisition. Different types of MLU are suitable for different languages, but Czech, a morphologically complex Slavic language, has not been examined in this respect, nor most Slavic languages. Therefore, we compared MLU calculated in different units and based on different sample lengths and examined its properties by assessing the validity of MLU against other transcript and test-based language measures.  We analyzed transcripts of spontaneous language recordings produced by 109 children during free play with their parents at two time points: 2;6 years and then at 3;11 years (59 children at 3;7 and 50 at 4;3 years). We compared MLU in syllables, morphemes, and words (MLUw) in transcripts of different lengths, 50, 75, 100, and all available utterances (more than 30 utterances). To evaluate the validity of MLU, we also calculated the Index of Productive Syntax (IPSyn) and the number of different words (NDW) and used the results of the receptive vocabulary and grammar comprehension tests assessed at both time points. The different MLU measures based on different sample lengths correlated closely with MLU in transcripts of all utterances (all rs > .87). We found mostly strong correlations between MLU, IPSyn, and NDW at both time points and weak or moderate correlations between MLU and grammar and vocabulary. Regression models showed the significant unique effect of MLUw at 2;6 for MLUw (β = .29) and grammar (β = .33) at 3;11 and vocabulary (β = .27) at 3;7. Our results confirm that MLU in words based on all utterances is a valid measure of early language skills in Czech, as it is stable in time and shows concurrent and predictive relations with other transcript-based and test-based measures.

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Photo by Sebastian Pandelache on Unsplash

Photo by Sebastian Pandelache on Unsplash

Why is it important?

Our results confirm that MLU in words based on all utterances is a valid measure of early language skills. This is an important finding as an automatic calculation of MLU in morphemes or syllables in highly inflectional languages such as Czech is complicated. Additionally, using MLU from complete language samples enable examining the language skills of the less talkative children or children with language impairments.