Mean length of utterance (MLU) is widely used in child language sample analysis as a way to quantify language development. The current study examines the split-half reliability of MLU and two alternative measures: MLU2 and median length of utterance (MdLU). The effects of utterance segmentation into phonological units (P-units) or communication units (C-units) on reliability were also studied. Sixty conversational child language samples were used which included ten children with language impairment. All measures were found to have high levels of split-half reliability, with MLU and MLU2 having higher levels of reliability than MdLU. There was no significant difference between MLU and MLU2. The differences in reliability when segmented into P-units or C-units were inconsistent. Overall, MLU and MLU2 are adequately reliable measures for clinical use.

Concerns regarding Mean Length of Utterance (MLU) has led to adaptations of this method of analysis. A recent study by Johnston (2001) introduced an alternative to MLU called MLU2. The current study investigates the split-half reliability of MLU and MLU2 as well as another alternative, Median Length of Utterance (Med-LU). Split-half reliability was found for these methods when segmented into Phonological and Communication Units. Split-half reliability of MLU2 was generally higher than that of MLU, and both were higher than Med-LU. The study suggests that MLU2 may also be a valuable tool for clinicians in analyzing child language.