These days, making statements about progress are increasingly important as we seek to document our efforts in each and every practice setting where SLPs and audiologists serve individuals with communication disorders. To that end, using scores that are sensitive to smaller changes in performance over time are critical. There are a number of Pearson products that currently have growth scores:
But what exactly is a growth score, and how is it used? Using the PPVT-4 test as an example, you can read a brief excerpt from the test manual for a definition below. In the case of the PPVT-4 and EVT-2, the growth score is titled “Growth Scale Value” or GSV:
The GSV score is useful for measuring change in…performance over time. The GSV is not a normative score, because it does not involve comparison with a normative group. Rather, it is a transformation of the raw score and is superior to raw scores for making statistical comparisons (p.18).
For a little more background on growth scores, you can read another set of comments in the PPVT-4 test manual regarding the GSV:
The GSV scale was developed so that vocabulary growth could be followed over a period of years on a single continuous scale. Standard scores, percentiles, stanines, and NCEs compare an examinee’s vocabulary knowledge with that of a reference group representing all individuals of the same age or grade. In contrast, the GSV measures an examinee’s vocabulary with respect to an absolute scale of knowledge. The test performance of any examinee…can be placed on a [single] GSV scale. As an examinee’s vocabulary grows, the GSV will increase.
The GSV is an equal-interval scale. Therefore, GSV scores can be added, subtracted, or averaged. Furthermore, the fact that GSVs can be averaged makes this scale a useful one for tracking the progress of groups.
Standard scores and percentiles are less useful than GSVs for measuring growth, because the reference norm group changes as the examinee moves into a higher age or grade level. If a person’s vocabulary increases at the average rate, his or her standard score and percentile would stay the same, whereas the GSV score would increase (p.21).
In addition, each test manual should offer you the number of growth points needed to show statistically significant change at a particular age level. For example, 8 GSV points of change from one test administration to another is statistically significant on the PPVT-4 for individuals age 2:6-12. For children in this age range, if they increase 8 points on the GSV scale, you can be confident that the child’s vocabulary has truly increased.
A caveat: Using growth scores for measuring progress doesn’t mean standard scores are not important. Standard scores serve a very clear purpose and can be used reliably with growth scores. You can think of a growth score as a complementary tool to a standard score; each score tells you something different about the individual’s performance and creates a clearer picture of change over time. The growth score indicates whether there has been improvement, and the standard score indicates whether the rate of improvement has been above or below the average rate for the child’s peers.
So, as you consider the need to demonstrate growth in an individual you serve, do consider using the growth scores available in the above tests as well—and make your work easier!
Dunn, L. M. & Dunn, D. M. (2007). PPVT-4 Manual. Bloomington, MN: NCS Pearson, Inc.