Abstract
Mean length of the utterance (MLU) and Index of productive syntax (IPSyn) are well-established measures of language acquisition. We examined the use of these measures for child language transcripts in Czech and relations between them and other language tests.
We compared MLU in syllables, morphemes, and words and applied IPSyn adapted to Czech on the same transcripts. We used a corpus of 110 children recorded during free play at two time points: 2;6 years and then at 3;8 (60 children) and 4;4 years (50 children).
The children were tested for receptive vocabulary and grammar. The different MLU measures correlated closely (all r's > 0,97), so we used MLU in words in further analyses.
We found strong correlations between transcript-based measures of MLU and IPSyn in both time points (0.88 and 0.77). Both MLU and IPSyn in 2;6 years predict themselves in 3;8 and 4;4 years (β = 0.37 and 0.35 respectively).
In the case of IPSyn, the vocabulary test showed a unique effect above and beyond the factors of other predictors (β = 0.37), in the case of MLU, it was at the limit of significance. Our results confirm that MLU in words is an adequate measure.
This is an important finding as an automatic calculation of MLU in morphemes or syllables in highly inflectional languages as Czech is complicated. IPSyn seems to be a valid measure since it predicts itself in time with a vocabulary measure as a unique predictor and it also correlates closely with a transcript-based measure such as MLU.