Linguistics Research Today is a free monthly online journal that collates and summarizes the latest research about Linguistics, including details on human language, phonetics, syntax, phonology.

A closer look at MLU: what does it really measure?

Dethorne LS, Johnson BW, Loeb JW

Pennsylvania State University, University Park, Pennsylvania 16802-3100, USA. lsd12@psu.edu

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. 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 28-37 months. Regression techniques were employed to predict MLU from number of different words (NDW) and a tense accuracy composite (TAC). Depending on whether the variable was acting alone or in concert with the other, TAC accounted for 23% or none of the variance in MLU, while NDW accounted for 51% or 28%. We offer three potential explanations for the observed association between MLU and NDW, none of which necessarily precludes the others.

Published 8 September 2005 in Clin Linguist Phon, 19(8): 635-48.
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