Identifying “disorder within diversity”

This month, ASHA’s Language, Speech, and Hearing Services in Schools journal put out a (free!) clinical forum on the concept of “disorder within diversity.” The forum includes an introduction, where you can read about the usefulness of moving away from “difference vs. disorder,” and five related research articles. Here we review one of the articles, and others can be found here, here, and here.

Do you like your grammatical morphemes accurate, diverse, or productive?

So, you’re an awesome clinician who is eliciting and analyzing a language sample from a bilingual preschooler. High five for you! You want to capture some data about their grammar skills. What exactly do you measure?

The authors of this study suggest that, rather than counting up how accurate the child’s use of tense and agreement markers is (so, finding the percentage of accurate uses out of total obligatory contexts), you instead focus on the diversity and productivity of tense/agreement markers. The morphemes we’re concerned about are:

  • third person singular –s
  • past tense –ed
  • copula BE (am, are, is, was, were)
  • auxiliary DO (do, does, did)
  • auxiliary BE (am, are, is, was, were).* 

Notice there are five morphemes and 15 total forms here; that’ll be important in a second. These morphemes are clinical markers for language disorders in English.  

So what are diversity and productivity, and how do you measure them? Enter tense marker total and TAP score. We’ll give the basic gist of both, but the specifics for calculating them came from Hadley & Short (2005).

  • Diversity (tense marker total): How many of those 15 forms from earlier did the child use in the language sample?
  • Productivity (tense/agreement productivity, or TAP score): How many different ways did the child uses those five morphemes? Up to five points allowed per morpheme, for a max of 25.

The authors found that, for a group of 4-year-old Spanish–English bilingual children, tense marker total and TAP scores:

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  • Were correlated with MLU(words) and NDW (number of different words), valid LSA measures for this population
  • Changed over the course of a school year
  • Looked different for children with and without parent-reported language concerns

The article provides group means (typical language vs. language concerns) for both measures, but not true normative or diagnostic data, so you can’t use tense marker totals or TAP scores to directly diagnose a language disorder at this point. However, consider using them as criterion-based measures to describe tense and agreement skills, identify morphemes to focus on in therapy, and monitor growth.

*If you’re having one of those days and can’t remember the difference between a copula and auxiliary—no sweat. A copula is the only verb in a clause (like is was, there), but auxiliaries are those “helping verbs” that are linked up with another verb (like are was with linked, there).

Potapova, I., Kelly, S., Combiths, P. N., & Pruitt-Lord, S. L. (2018). Evaluating English Morpheme Accuracy, Diversity, and Productivity Measures in Language Samples of Developing Bilinguals. Language, Speech, and Hearing Services in Schools, 49(2), 260–276. https://doi.org/10.1044/2017_LSHSS-17-0026.