Home | Clinical Café Archive | December 2003

Insights from Pearson—Reporting Test or Subtest Data . . . What's the Difference?

Clinical Café by Tina Eichstadt, M.S., CCC-SLP

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"I only gave three of the subtests on Bobby's language test because I'm really short on time these days. I got what I needed for information so I stopped testing. I also like to pick and choose the subtests that I prefer." How many of us have said something similar to these statements during our careers? Maybe it was years ago, maybe it was yesterday. No matter. After a behind-the-scenes look at tests vs. subtests in this article, we will all be able to collectively exclaim, "Eeek! What was I thinking?!?"

Simply Stated

For the purposes of test scoring, interpretation, and reporting, a test can stand alone, but a subtest cannot. You may report and interpret scores on a single test or composite of specific subtests (based on the test manual), but not on a single subtest. Why? Because good psychometricians say so. Just kidding . . . read on!

The term subtest implies rather clearly that its content is not complete on its own-it is a "sub" of something else. A subtest measures only a portion of the content area you are trying to assess, and measures that content in a particular way. Student performance on a subtest is only a part of the picture that clearly describes a student's performance on an area of content, and therefore must be linked to the rest of the data that will fill in the picture and make the information reliable, valid, and able to be communicated quantitatively. A single subtest score (other than the raw score) is generally not reported because it is not reliable enough to stand alone. The subtest must be given in conjunction with other subtests to form a composite or total test score.

The term test refers to a set of data that is strong enough in validity and reliability to report a separate set of scores for the items and call it a test. Tests are collections of subtests and/or a set of items with statistically valid and reliable item data. Multiple tests linked and published together are often called a test battery. The CASL is a good example of a test battery with 15 highly-reliable tests, not subtests, all independently rigorous and able to stand alone or together in scoring, interpretation, and reporting.

Decisions YOU Make in Testing

Here's an example: Basic Concepts and Synonyms are two individual tests within the CASL. You could administer one or both of these tests, score each, interpret each individually with respect to their broad content area (Lexical/Semantic), or use the Syntax Construction and Pragmatic Judgment tests with the Basic Concepts test to establish a Core Composite for a 3-year-old. If you were particularly concerned about an additional area of language, you could then give a single Supplementary Test, and the scores are valid and reliable on their own, outside the Core Tests but psychometrically linked. The benefits of using independent tests in a battery include: (1) the ability to tease out each content area individually with data that is valid and reliable; (2) a data-based "profile" of student performance that is linked to a nationally representative normative sample; and (3) an opportunity to "kill two birds with one stone" by documenting norm-referenced data while pointing directly to intervention needs. There are likely even more benefits beyond these. Very seldom would anyone need to administer an entire battery of tests. The clinician is free to give one test or several tests and can report the score(s) with confidence. You do not have this flexibility when working with subtests.

A clarifying caveat: If you choose to give only a few subtests randomly on a test, you may not score, average, or report normative data on those subtests. You can, however, use the test information qualitatively or in a criterion-referenced format. Use A description of the student's performance, not numeric data. Because the standardization procedure was not followed, the norms will be invalid and unusable. If you need a standardized score for eligibility or release from services, make sure you follow the standardization procedure, give the whole test (or COMPLETE set of SUBtests), and report accurately.

So the moral of the story is . . . know your test! The manual should tell you in the first few sentences if you are working with tests or subtests and how they are combined. Follow the rules, and get scores you can use. It's that simple.

Send us your "What I'd like to learn about tests this year" list

As your partner in testing, we'd like you to know what we do, how we do it, and why. In turn, we'd like to know what other information we could provide to help you in your jobs. So send us your "What I'd like to learn about tests this year" list to webmaster@agsnet.com. And we'll try to fulfill your wishes.

SLP Discussion Center

As always, we'd like to thank you for your ongoing service to people with communication needs and to remind you that we are here to support you with that effort. If you'd like to discuss this topic further, please feel free to use the SLP Discussion Center as the vehicle for an ongoing discussion with your colleagues. Should you have questions regarding these or other Pearson Speech and Language products, we welcome your phone calls at 800-627-7271 or use our web site at http://ags.pearsonassessments.com.