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Mean Length of Utterance (MLU)



Mean length of utterance (MLU) is the average number of morphemes per utterance. It is an index of expressive language development used beyond the stage of single words, when a child uses two or more words together in an utterance. It is calculated in 100 spontaneous utterances by counting the number of morphemes in each utterance divided by the total number of utterances. MLU is used as a benchmark to assess individual differences and developmental changes in grammatical development in children in the early stages of language acquisition. Children with autism frequently demonstrate differences in MLU compared to non-autistic developmentally delayed children and typically developing children by producing shorter utterances with fewer grammatical morphemes. Recent research has acknowledged the use and utility of using MLU as an index for language development in children with autism (Condouris, Meyer, & Tager-Flusberg,