Grammatical morpheme effects on MLU: "the same can be less" revisited

Area of Science:

• Child language development
• Linguistic pathology
• Developmental psychology

Background:

• Studies on specific language impairment (SLI) often use age-matched and mean length of utterance (MLU)-matched typically developing children as controls.
• Grammatical morpheme use is a common dependent measure, but it is correlated with utterance length.

Purpose of the Study:

• To investigate whether specific language impairment (SLI) in children is masked by mean length of utterance (MLU) matching.
• To examine the necessity of "offsetting effects" in language development research.

Main Methods:

• The study involved two experiments comparing children with SLI to typically developing children.
• Analysis focused on grammatical morpheme use and other linguistic features in relation to MLU.

Main Results:

• Children with SLI did not necessarily show deficits across all linguistic measures when compared to MLU-matched peers.
• The study demonstrated that MLU matching can obscure differences in specific language skills.
• Offsetting effects, where a deficit in one area is compensated by a strength in another, are not always required in MLU-matched comparisons.

Conclusions:

• Mean length of utterance (MLU) matching in specific language impairment (SLI) research may not accurately reflect a child's overall language abilities.
• Researchers should consider alternative matching methods or a broader range of linguistic measures to avoid masking true SLI characteristics.
• The findings challenge the assumption that MLU-matched controls always provide a valid comparison group for SLI studies.