An establishment of embedded symptom validity testing within the Delis-Kaplan Executive Functioning System
Patients involved in litigation or seeking worker's compensation are routinely evaluated to determine the presence and severity of cognitive impairment. Research has documented that nearly 40% of these patients attempt to feign or exaggerate cognitive impairment during neuropsychological examination. This particular response bias makes it difficult for neuropsychologists to provide valid diagnoses and recommendations. Symptom validity tests (SVT) are well validated tests that have been created to assess noncredible performance; however none of these measures are embedded within the Delis-Kaplan Executive Function System (D-KEFS), a popular battery of executive functioning. Overall, this study supported the use of embedded symptom validity testing in the D-KEFS Trail Making and Verbal Fluency subtests, as their conditions identified an adequate percentage of noncredible performers while maintaining a low rate of false-positive errors. The extent to which D-KEFS subtests may be used dually as an embedded symptom validity measure was directly linked to its complexity and difficulty, as easier tasks of executive function possessed better sensitivity and specificity rates. The results of this study strongly support the use of proposed cutoffs of the D-KEFS Trail Making and Verbal Fluency conditions, particularly those of less complexity, as they demonstrated the ability to accurately discriminate between credible and noncredible performers. Based on the findings of this study the use of these subtests is recommended, as they allow for dual assessment of symptom validity and executive functions. Provided that future replication is successful, the identified D-KEFS embedded symptom validity measures may be used to validate patient performance within neuropsychological examination and thus increase our confidence regarding diagnostic findings.
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