Home | Clinical Café Archive | November 2007

Parallel Forms: What They Can Do For You

November 2007 Clinical Café
By Jeff Evans, MS, CCC-SLP

Do you ever wonder about test forms when you pick up a test? Why does it matter if a test has two (or more) forms? Is it really worth the effort to figure out what to do with Form A and Form B? Does it really matter if a test has two forms?

Short answer: Yes, it matters, and yes, it’s worth the effort.

We’ll help you through the basics of test forms in this Clinical Cafe. We’ll explain the differences between forms, how to use Forms A and B, and what they can mean for your clinical practice.

Parallel forms of a test are statistically equal (or as equal as they possibly can be) in their ability to measure the target content area. “Alternate forms reliability” refers to the correlation between Form A and Form B; that is, how closely your results from each form would match if you gave them to the same person. The correlation (written as a decimal between .00 and 1.00) should be as close to 1.00—a perfect correlation—as possible; for high quality tests like the PPVT-4™ test and EVT-2, the correlation is 0.89 across all ages. Therefore, you should be able to give a student Form A or Form B from the same test and get very nearly the same score using either form.

So what is the difference whether you have Form A or Form B or both? Your options for timely and accurate evaluation expand when you own both forms. All you need to decide is which form to use first. If they are truly equivalent, or “parallel,” it won’t matter which one you choose. If you want to test the same student again in the same content area within a short timeframe (several weeks), as in the case of progress monitoring, use the alternate form. If you wait longer (months) before testing the same student again, you may be safe to use the same form again.

We’ve covered the development and appropriate use of parallel forms. But what is the value of parallel forms in your clinical work? You get more flexibility. You can get more frequent use out of the quality test you purchased. Consider just two scenarios: special client needs; and progress monitoring. You may have a student who you know to be bright, precocious, with a good memory. If you need to test this child again you could expect him/her to recall items, particularly pictures; possibly even perseverate on a particular picture. This is the time to use your alternate form.

Use of alternate forms for progress monitoring opens new horizons for your practice. Now you can use a test such as the PPVT-4™ or the EVT-2 for progress monitoring, without concern that your student will learn the test and invalidate the scores. Form B contains a different set of items, with scores on the same scale as Form A, and the scores can be compared equally. You can monitor the progress of your student’s ability more often, and be accurate and reliable in your measurement by using Form A and Form B. This can enhance your use of response-to-intervention (RTI) procedures. A test such as PPVT-4™ with Forms A and B becomes a Tier 2, and a Tier 3 RTI tool, using the alternate forms.

So, is it worth the effort to figure out what to do with Form A and Form B? And does it really matter if a test has two forms? It certainly is worth the effort, because it allows you to work smarter, and be more accurate in your assessment of children.

SLP Discussion Center

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