Language Disorder Assessment: MLU, DSS, and TTR Analysis
This paper presents a clinical language assessment of Jay, a 3-year 5-month-old boy with a history of expressive language delay, using a sample of 25 intelligible utterances gathered during a clinic observation. The analysis applies four standard measures: Mean Length of Utterance (MLU), Developmental Sentence Score (DSS), Correct/Incorrect Form Analysis based on Brown's morphemes, and Type Token Ratio (TTR). Results across all four measures place Jay within or near normal developmental limits for his age. The paper concludes with a summary report, practical intervention recommendations for parents and educators, and measurable six-month goals, ultimately recommending a wait-and-see approach with re-evaluation at six-month intervals.
- Mean Length of Utterance (MLU): MLU score calculated and compared to norms
- Developmental Sentence Score (DSS): DSS score places Jay at 50th percentile
- Correct/Incorrect Form Analysis: Missing morphemes assessed against Brown's stages
- Type Token Ratio (TTR): TTR within normal range with sample caveats
- Summary Report and Recommendations: Clinical summary, goals, and wait-and-see recommendation
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What makes this paper effective
- The paper systematically applies four distinct, well-established clinical measures (MLU, DSS, Correct/Incorrect Form Analysis, and TTR) and clearly explains the rationale behind each calculation, making the methodology transparent and reproducible.
- The summary report ties together all four measures into a coherent clinical picture, acknowledging limitations such as the small utterance sample while still reaching a defensible recommendation.
- Practical, specific scaffolding suggestions for parents and educators (e.g., modeled sentences using past tense) demonstrate applied clinical thinking beyond raw score interpretation.
Key academic technique demonstrated
The paper demonstrates norm-referenced interpretation — comparing an individual child's scores against published developmental benchmarks (Rice et al., 2010) and percentile cutoffs — while also acknowledging the constraints of a small sample. This balance between quantitative scoring and qualitative clinical judgment is central to speech-language pathology practice.
Structure breakdown
The paper moves from discrete quantitative analyses (MLU, DSS, TTR) to a synthesis section (Summary Report) that integrates all findings into clinical recommendations and measurable goals. Each analytical section follows a consistent pattern: present the score, explain the calculation, reference normative data, and note limitations. The summary then reframes the findings in plain language suitable for a clinical report audience.
Mean Length of Utterance (MLU)
The mean length of utterance in Jay's sample of 25 meaningful utterances is 3.8 or 3.5. Three uses of slang (gotta, gonna) by Jay increase the count to 83 morphemes, which results in a score of 3.8. If these slang words were considered one morpheme each, the rate would be 3.5. However, since the meaning of the slang words is compound — as in "got to" or "going to" — they may each be counted as two morphemes. The MLU for words (MLUW) for children with language impairment in the age range of 3;0 to 3;5 years is 2.84. Jay's MLUW falls between the age ranges of 5;0 to 5;5 years and 5;6 to 5;11 years for children with language impairment, which show MLUM scores of 3.72 and 3.95, respectively (Rice et al., 2010). The MLUM for children without language impairment has been shown to be higher in each age range (Rice et al., 2010). Accordingly, Jay's MLUM can be considered within typical limits. The main caveat in this analysis is that 25 intelligible utterances is low; research standards recommend a sample of more than 50 utterances (Rice et al., 2010).
The table below, drawn from Rice et al. (2010), presents normative MLUW and MLUM values for children with language impairment across age ranges:
MLUW and MLUM by Age Range for Children with Language Impairment (Affected Group)
Age 2;6–2;11 (N=6): MLUW Mean 2.37, SD 0.32, Cohen's d 0.93; MLUM Mean 2.59, SD 0.39, Cohen's d 0.90.
Age 3;0–3;5 (N=15): MLUW Mean 2.84, SD 0.38, Cohen's d 0.97; MLUM Mean 3.07, SD 0.48, Cohen's d 1.07.
Age 3;6–3;11 (N=24): MLUW Mean 3.10, SD 0.75, Cohen's d 1.04; MLUM Mean 3.36, SD 0.80, Cohen's d 1.09.
Age 4;0–4;5 (N=54): MLUW Mean 3.31, SD 0.70, Cohen's d 1.22; MLUM Mean 3.64, SD 0.80, Cohen's d 1.22.
Age 4;6–4;11 (N=72): MLUW Mean 3.60, SD 0.62, Cohen's d 0.95; MLUM Mean 3.95, SD 0.70, Cohen's d 1.01.
Age 5;0–5;5 (N=84): MLUW Mean 3.72, SD 0.61, Cohen's d 1.05; MLUM Mean 4.09, SD 0.70, Cohen's d 1.10.
Age 5;6–5;11 (N=97): MLUW Mean 3.95, SD 0.60, Cohen's d 0.85; MLUM Mean 4.34, SD 0.67, Cohen's d 0.89.
Source: Rice et al., 2010.
Developmental Sentence Score (DSS)
DSS Score = number of points ÷ number of utterances.
Jay's Developmental Sentence Score based on the 25-utterance sample is 100 points divided by 15 sentences, yielding a score of 6.67. One limitation of this analysis is that the DSS is normed on a 50-utterance sample. Only children who score below the 10th percentile, or more than one standard deviation below the mean, are typically considered to need intervention. Jay scores at the 50th percentile, which corresponds to a benchmark score of 6.64 for a child aged 3 years and 6 months.
Correct/Incorrect Form Analysis
Jay's speech sample notably lacks use of past tense, third person, possessives, contractible copula, and contractible auxiliary phrases. Referencing Brown's morphemes, Jay's use of language corresponds with the age-of-mastery range of 28 to 46 months. At 41 months of age, Jay is approaching the upper end of this range, but his expressive language appears to be developing normally. It is possible that the language sample did not produce many opportunities for Jay to use past tense, as he appears to be narrating his play — perhaps interacting with objects while an adult looks on.
References
Rice, M. L., Smolik, F., Perpich, D., Thompson, T., Rytting, N., & Blossom, M. (2010, April). Mean length of utterance levels in 6-month intervals for children 3 to 9 years with and without language impairments. Journal of Speech, Language, and Hearing Research, 53(2), 333–349. doi: 10.1044/1092-4388(2009/08-0183). PMCID: PMC2849178. NIHMSID: NIHMS120034.
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