The psychometric properties of internal consistency, stability coefficients and alternate-form reliability related to the D-KEFS instruments are presented in the Technical manual which accompanies the D-KEFS kit.
These measures of reliability provide the basis for deriving the standard error of measurement and confidence intervals for the test. The applicability of specific reliability methodologies varied across D-KEFS tests depending on the nature and procedures of the task.
The studies completed with the different age groups showed that the reliability of the different subtests was largely within the moderate to high range.
The nine tests comprising the D-KEFS are either relatively new or modifications of long-standing clinical or experimental tests.
The validity of D-KEFS instruments that are modified tests (i.e., the Stroop procedure, Trail Making Test, verbal and design fluency tests, tower tasks, the 20-questions procedure and proverb interpretations) has been demonstrated in numerous neuropsychological studies conducted over the past 50 years or more.
Evidence of the validity of these procedures has been provided in terms of the sensitivity of the tests to measure important areas of higher-level executive functions.
Validity studies presented in the Technical manual report correlation studies including:
- intercorrelations of measures within individual D-KEFS tests
- correlations between measures of different D-KEFS tests
- correlations of the D-KEFS with other cognitive tests including California Verbal Learning Test – Second Edition (Delis, Kaplan, Kramer & Ober, 2000) and the Wisconsin Card Sorting Test (Heaton, Chelune, Talley, Kay & Curtiss, 1993).
A clinical pilot study is also discussed in the Technical manual. This was carried out to assess the D-KEFS profiles associated with Alzheimer’s disease and Huntingdon’s disease. Findings from this preliminary study suggested that dissociations in executive function profiles across different types of patients can be captured by the D-KEFS achievement and process measures.
Some researchers have criticised the limited clinical data presented in the original publication manual (e.g., Schmidt, 2003).
In response, Delis, Kramer, Kaplan and Holdnack (2004) pointed out that much of the test development and validity data for the D-KEFS had appeared in the mainstream neuropsychology literature rather than the test manual itself, where it was available for peer review and open to scientific critique.
The new D-KEFS Examiner’s manual includes a review of this research reported by Delis et al (2004) and more recent papers that have cited the use of the D-KEFS. The evidence from these studies further argues for the clinical utility of the D-KEFS.
Delis, D. C., Kaplan, E., Kramer, J., & Ober, B. A. (2000). California Verbal Learning Test-Second Edition (CVLT-II). San Antonio, TX: The Psychological Corporation.
Delis, D.C., Kramer, J.H., Kaplan, E. & Holdnack, J. (2004). Reliability and validity of the Delis-Kaplan Executive Function System: An Update. Journal of the International Neuropsychological Society, 10, 301-303.
Heaton, R. K., Chelune, G. J., Talley, J. L., Kay, G. G., & Curtiss, G. (1993). Wisconsin Card Sorting Test manual – Revised and expanded. Lutz, FL: Psychological Assessment Resource, Inc.
Schmidt, M. (2003). Hit or miss? Insight into executive functions (Test Review). Journal of the International Neuropsychological Society, 9, 962–964.