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An Additional Word About Interpreting GFTA™-2 Scores

Since the publication of the GFTA-2, questions have been raised about the difference between scores on the 1986 edition of GFTA and the GFTA-2. The 1986 GFTA norms were percentiles extrapolated from two different databases: the National Speech and Hearing Survey (Hull, Mielke, Willeford, & Timmons, 1976) and the Khan and Lewis work of 1986. (See Chapter 2 in the GFTA-2 manual for a complete history of the GFTA.) The use of two unrelated databases collected at two different points in time is part of the reason for score differences. However, the key reason for the difference in scores lies in how the normative scores were developed.

The psychometrician who worked on the original GFTA norms apparently applied the methods of normative score development based on a "normal" distribution of data. He/she may have done this because of a lack of familiarity with articulation or because this was the known and widely accepted procedure for developing test scores at that time. In either case, this method did not result in scores that appropriately represented the extremes of the distributions of articulation errors. For example, according to the 1986 norms, a female who was aged 6 years 6 months and made no errors would have a percentile rank of 99. This would mean that only 1 percent of girls that age made no errors. Of course, this is not true. According to the GFTA-2 norms, the percentile for girls this age making no errors is appropriately listed at >65. This means that, at this age, 65 percent make one or more errors and 35 percent make no errors. Speech pathologists know, and research on normal articulation development tells us, that this is a more accurate representation.

If a child has a percentile rank of 2 on the 1986 GFTA or on another articulation test with scores developed by "forcing the data" into a normalized distribution-this would equate to a standard score of 70. This score is two standard deviations (SDs) below the mean and represents a significant difference or distance from average. For example, a boy with a severe articulation problem who is aged 4 years 6 months and gets a standard score of 70 on the GFTA-2 would have a percentile rank of 6. This score is "equivalent" to the percentile rank of 2 on a "normalized" distribution or on a test developed by those means. In either case, this child's articulation is significantly different from normal or average and is in need of remediation.

References:

Hull, F. M., Mielke, P. W., Jr., Willeford, J. A., & Timmons, R. J. (1976). National Speech and Hearing Survey (Final report for USOE Project No. 50978, Grant No. OE-32-15-0050-5010 [607]). Washington, DC: Bureau of Education for the Handicapped (DHEW/OE). (ERIC Document Reproduction Service No. ED 129 045)

Khan, L. M. L., & Lewis, N. P. (1986). Khan-Lewis Phonological Analysis. Circle Pines, MN: AGS Publishing.