Mean Length of Utterance (MLU)

Language Development Analysis

Overview

  • Language development is analyzed through transcripts of language samples from adults and children.

  • Historically, samples needed to be at least 15 minutes long and contain 100 utterances.

  • Current research indicates that a 50-utterance sample is adequate for analysis.

Mean Length of Utterance (MLU)

  • MLU is the average number of free and bound morphemes in an utterance.

  • Changes in linguistic development correlate with increases in utterance length.

Brown's Stages of Language Development

  • Developed by Roger Brown, establishing essential milestones for morphological and syntactical growth.

  • Based on a study from the 1970s involving three children observed over four years.

  • Results have been replicated, confirming the applicability of the stages.

Key Milestones in Brown's Stages

  1. Stage I (12-26 months; MLU 1.0-2.0)

    • One-, two-, and three-word utterances

    • Uses intonation for yes/no questions

    • Limited wh- questions

  2. Stage II (27-30 months; MLU 2.0-2.5)

    • Begins to use grammatical morphemes

    • Uses "in" and "on"

  3. Stage III (31-34 months; MLU 2.5-3.0)

    • Increased utterance length through auxiliaries

    • More frequent wh- questions

    • Interrogative reversals

  4. Stage IV (35-40 months; MLU 3.0-3.75)

    • Uses object-noun-phrase complements

    • Indirect or embedded wh- questions

  5. Stage V (41-46 months; MLU 3.75-4.5)

    • Coordinates simple sentences

    • Uses locatives (e.g., up, down)

    • Uses "and" as the main conjunction

  6. Stage V+ (47+ months; MLU 4.5+)

    • Adds negative interrogatives

    • Introduces indefinite forms (e.g., nobody, no one)

    • Faces challenges with double negatives

Summary

  • The milestones provide guidance for assessing children's linguistic development and targeting MLU at different age ranges.

  • For example, a 3-year-old should have an MLU of 3.0 to 3.75.