science

Mean length of utterance

Mean length of utterance is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mean length of utterance rather than just read about it. In short: Mean length of utterance (or MLU) is a measure of linguistic productivity in children. It is traditionally calculated by collecting 100 utterances spoken by a child and dividing the number of morphemes by the number of utterances.

Key takeaways

Mean length of utterance belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mean length of utterance to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mean length of utterance from memory before moving on to harder problems.

Reference excerpt

Mean length of utterance (or MLU) is a measure of linguistic productivity in children. It is traditionally calculated by collecting 100 utterances spoken by a child and dividing the number of morphemes by the number of utterances. A higher MLU is taken to indicate a higher level of language proficiency. The mean length of utterance (MLU) was proposed by Roger Brown (1973) as a better index for language development in children than age. Mean length of utterance is a good marker of language impairment. It is the number of words or morphemes in each of their spontaneous utterances. It can be used to benchmark language acquisition and is used to compare language intervention outcomes in children with autism. In testing of children ages 3–9 with diagnoses of autism or autism spectrum disorders and nonverbal IQ scores below 85, results indicated that children with autism persistently scored below the unaffected group without significant improvement in scores concerning mean length of utterance. There may be variability in outcomes due to sampling differences. A study by Bishop and Adams (1990) suggests that MLU at 4.5 is a good predictor of reading ability at age 8. Nonetheless, MLU is considered controversial, and should not be used as the only diagnostic measure of language proficiency in children.

See also Language acquisition Language development

References

Bishop, D. V. M., & Adams, C. (1990). A prospective study of the relationship between specific language impairment, phonological disorders and reading retardation. Journal of Child Psychology and Psychiatry, 31, 1027–1050.

External links The Effect of Coffee Consumption on Adults’ Average MLU at the Breakfast Table: A humorous article demonstrating some of the criticisms of MLU—namely that extra-linguistic factors can greatly affect MLU.

Worked examples

Example 1 — a first encounter with Mean length of utterance

Start with the simplest possible case. Write down what Mean length of utterance claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mean length of utterance before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mean length of utterance ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mean length of utterance

In research: Mean length of utterance appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mean length of utterance in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mean length of utterance is common in secondary-school and first-year university syllabi. It links to neighbouring topics Morphemes, Phonetics stubs, Reading (process), so understanding it makes those chapters shorter.
In everyday life: Look for Mean length of utterance outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mean length of utterance in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mean length of utterance means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mean length of utterance out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mean length of utterance in simple terms?

Why does Mean length of utterance matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mean length of utterance?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mean length of utterance.