Mean length of utterance (MLU) is a measure that describes language production in terms of utterance length, initially as the average number of words and later as the average number of morphemes spoken per utterance. It is a language sample analysis tool that is used both clinically and in research. This entry provides an overview of MLU, including its history, calculation procedures, score interpretation, use with clinical populations, and application to other languages.


Early child language researchers noted a rise in the number of words spoken in a single utterance along with increases in chronological age, where younger children spoke fewer words per utterance than older children. This resulted in the use of utterance length as a measure of a child’s language development. Given this general ...

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