title: A closer look at MLU: what does it really measure?
abstract: 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.
authors.affiliation: Pennsylvania State University, University Park, Pennsylvania 16802-3100, USA. lsd12@psu.edu
authors.forename: Laura S
authors.initials: LS
authors.lastname: Dethorne
authors.forename: Bonnie W
authors.initials: BW
authors.lastname: Johnson
authors.forename: Jane W
authors.initials: JW
authors.lastname: Loeb
mesh_terms: D002663:Child Language; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008037:Linguistics / Q000379:methods*; D008297:Male; D014705:Verbal Behavior; D014825:Vocabulary