What does mlu measure

This study explored the extent to which variance in MLU could be accounted for by a measure of expressive vocabulary and a measure of morphosyntax in a group of 44 typically-developing children, ages months. We offer three potential explanations for the observed association between MLU and NDW, none of which necessarily precludes the others. A closer look at MLU : What does it really measure?

In addition, thanks to Marc Fey and the many members of his research lab that made the data collection for this project feasible and fun. Last but by no means least, thanks to the children of Kansas and their families who made this study possible. N2 - Despite the common use of mean length of utterance MLU as a diagnostic measure, what it actually reflects in terms of linguistic knowledge is relatively unclear.

AB - Despite the common use of mean length of utterance MLU as a diagnostic measure, what it actually reflects in terms of linguistic knowledge is relatively unclear. A closer look at MLU: What does it really measure? Laura S. The high correlations found between MLU3-w, MLU3-m and the scales of vocabulary, verbal morphology, nominal morphology as well as with the section of multiple choice items regarding children's advance in the acquisition of some particular structures revealed an extremely strong internal consistency throughout the two parental questionnaires.

Such a consistency proves, first, parental reports' trustworthiness when reporting about their children's language use and, second, BCDI instruments' reliability. The first prediction—that MLU3 scales in BCDI would be as sensitive as the rest of the scales in this instrument in detecting toddlers' developmental changes—has been confirmed by the data analyzed.

Moreover, MLU scales were calculated in exactly the same way in both instruments and revealed again a weaker effect of age in BCDI-3 than in BDCI-2, questioning the relevance of the methodological account for the differences mentioned.

The second explanation in terms of development appears to be much more convincing: the difference attested between the two Basque instruments is compatible with the stronger developmental changes taking place between the earlier developmental period covered by the BCDI-2 16—30 months , as compared to the later one covered by the BDCI-3 30—50 months.

The decrease in developmental speed found in the Basque data is in line with that found by Fenson et al. Note that two of the children studied by Brown reached that stage at around age 4, whilst the third one had reached it almost 2 years earlier.

Hence, this is compatible with the idea that the effect of this factor decreases after some age between 3 and 4 years.

On the other hand, the high correlations between MLU and the rest of the scales reveals the consistency of the instrument and its validity to measure children's verbal communicative development between 16 and 50 months of age in line with the results of many adaptations of the CDI-2 and CDI-3 instruments Fenson et al. Even though the explanation is not clearly formulated yet, we can conclude, in line with Dethorne et al. Its validity may be limited to the earliest stages, applying no further than Stage V.

Nonetheless, this last point could not be either confirmed or disconfirmed by the Basque data and requires further research. Based on the high correlations found in studies comparing MLU-w and MLU-m scores in several languages and even MLU counted in syllables , many authors consider that both MLU measures function equally well for measuring grammatical development Hickey, ; Aguado, ; Parker and Brorson, In contrast, Wieczorek considers that each MLU scale measures development in a different language component: MLU-w being more related to lexical development, and MLU-m to morphological development.

Our data support the former position. Moreover, regardless of measuring MLU3 in words or in morphemes, correlations between MLU3-m and the rest of the scales are almost identical to those between MLU3-w and the same scales, regardless of the lexical or grammatical character of them, in contrast to what has been suggested by Wieczorek The relations across MLU measurements and between MLU3-w and MLU3-m and the rest of scales may vary across languages or language types which differ in degree of morphological complexity and transparency agglutinative, fusionant, polysynthetic… , but such an analysis goes far beyond the scope of the current paper.

Utterance segmentation in words is much quicker and easier, since no technical descriptions are necessary, fewer decisions are required less subjectivity and variability across coders decreases considerably, in line with previous studies Hickey, ; Jackson-Maldonado and Conboy, , among others. The redundancy of using both, in addition to the ease of segmenting the utterance in words as compared to morphemes, leads us to recommend MLU-w as a more parsimonious measurement for screening in clinical studies, as has been suggested in other languages Hickey, ; Parker and Brorson, , without denying MLU-m's utility for more specific surveys in research.

The third hypothesis, that the relative amount of input would affect children's MLU, has been partially confirmed. MLU3 scales proved sensitive to detect input effects. A subsample of around children aged 18—48 months was analyzed with more detail in order to test MLU3's utility to test children's attained developmental level in the acquisition of a minority language in permanent contact with another socially dominant Romance language Spanish or French.

The data revealed MLU3-w and MLU3-m's sensitivity not only to age, already tested in Basque as in many other languages, but to the relative amount of exposure to the language. However, the effect of the amount of relative exposure to the language was not visible in the youngest child group 18—24 months.

Children who are exposed to more than one language rarely have the same amount of exposure to one of the languages as compared to age-matched monolinguals, on whom normative data are based Ezeizabarrena et al. As has been shown very convincingly by Pearson et al. The analysis of cross-sectional data obtained with the BCDI-2 16—30 months and BCDI-3 30—50 months of over children revealed a strong correlation between MLU3 and expressive vocabulary in both instruments, as well as between MLU3 and morphological scales.

The results also showed that MLU3-w and MLU3-m scales can report equally well on very young children's development in the Basque language up to age 4, which leads us to recommend the easier MLU-w measurement for clinical purposes. Finally, MLU3 subscales proved sensitive to input 25—48 months , which indicates the utility of these subscales to identify developmental patterns in Basque bilinguals aged 2—4. This study was approved by the ethics commission of the University of the Basque Country.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Finally, we are in debt to Maialen Iraola, the two reviewers and a native English speaker for their helpful comments. The remaining mistakes are our own. The analysis of the multiple choice item sections goes beyond the purpose of the current study.

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