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MMPI-2 Non-K-Corrected Scores

Doubts about the utility of the K correction have resulted in a renewed emphasis on examination and interpretation of non-K-corrected scores on the MMPI-2 Clinical Scales.  The procedure was developed in the early 1940s by Meehl and Hathaway to correct scores on the Clinical Scales for the effects of under-reporting. However, questions about its utility can be traced back to the initial validation data reported by McKinley, Hathaway, and Meehl (1948) who examined whether applying the K correction improved diagnostic accuracy and reported mixed results.  Subsequent research, reviewed by Dahlstrom and Welsh (1960), showed no improvement in differentiating patients from normals and in some cases (in criminal and delinquent groups in particular) applying the K correction actually weakened the distinctions between these two groups.

“The few studies available that provide cross-validational evidence on the K corrections have been based on cases in the latter [criminal justice] situations.   In these situations the K scale corrections do not seem to be beneficial, and may actually reduce the effective separations obtained without K corrections.” p. 154

In a later review, Dahlstrom, Welsh, and Dahlstrom (1972) reported that subsequent K-correction studies also did not support its utility.

Current MMPI-2 textbooks have also cautioned about the limitations of the K correction. Greene (2000) states:

“Little research justifies the continued widespread use of the K-correction of the Clinical Scales. Hopefully, future research will investigate this area more thoroughly …   clinicians probably need to avoid using K-corrections in settings in which normal persons are evaluated.” (p. 96)

Graham (2006) states:

“… it is this author’s recommendation that in non-clinical applications of the MMPI-2 both K-corrected and uncorrected scores be generated and that emphasis be placed on uncorrected scores when K-scale scores are significantly above or below average” (p. 225)

To facilitate consideration of scores on the non-K-corrected scores in MMPI-2 interpretation, the Extended Score Report provides both K-corrected and non-K-corrected Clinical Scale profiles.  Hand scoring materials for the non-K-corrected profiles are available as well.

Answers to frequently asked questions regarding non-K-corrected scores are listed on the MMPI-2 FAQs page.