title: Mean length of utterance levels in 6-month intervals for children 3 to 9 years with and without language impairments.
abstract: OBJECTIVE
  The mean length of children's utterances is a valuable estimate of their early language acquisition. The available normative data lack documentation of language and nonverbal intelligence levels of the samples. This study reports age-referenced mean length of utterance (MLU) data from children with specific language impairment (SLI) and children without language impairments.
  
  
  METHODS
  Of the 306 child participants drawn from a data archive, ages 2;6-9;0 (years;months), 170 were in the SLI group and 136 were in the control group. There were 1,564 spontaneous language samples collected, and these were transcribed and analyzed for sample size and MLU in words and morphemes. Means, standard deviations, and effect sizes for group differences are reported for MLUs, along with concurrent language and nonverbal intelligence assessments, per 6-month intervals.
  
  
  RESULTS
  The results document an age progression in MLU words and morphemes and a persistent lower level of performance for children with SLI.
  
  
  CONCLUSIONS
  The results support the reliability and validity of MLU as an index of normative language acquisition and a marker of language impairment. The findings can be used for clinical benchmarking of deficits and language intervention outcomes as well as for comparisons across research samples.
authors.affiliation: University of Kansas, Lawrence, KS 66045, USA. mabel@ku.edu
authors.forename: Mabel L
authors.initials: ML
authors.lastname: Rice
authors.forename: Filip
authors.initials: F
authors.lastname: Smolik
authors.forename: Denise
authors.initials: D
authors.lastname: Perpich
authors.forename: Travis
authors.initials: T
authors.lastname: Thompson
authors.forename: Nathan
authors.initials: N
authors.lastname: Rytting
authors.forename: Megan
authors.initials: M
authors.lastname: Blossom
mesh_terms: D000375:Aging; D002648:Child; D002663:Child Language; D002675:Child, Preschool; D016208:Databases, Factual; D005260:Female; D006801:Humans; D007360:Intelligence; D007361:Intelligence Tests; D007806:Language Disorders; D007807:Language Tests; D008137:Longitudinal Studies; D008297:Male; D013060:Speech; D013065:Speech Intelligibility; D013068:Speech Production Measurement; D013997:Time Factors