Abstract
Mean length of the utterance (MLU) and Index of productive syntax (IPSyn) are well-established measures of language acquisition. Different types of MLU are suitable for different languages but so far no one has compared which one is suitable for Czech. Likewise, IPSyn has not yet been adapted to many Slavic languages. We therefore compared MLU in syllables, morphemes, and words and we adapted IPSyn to the needs of Czech. We then examined the use of these measures and relations between them and other language tests for child language transcripts in Czech. 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 also 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 = 0.26), 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 such 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.