MMPI-2 scale F(p) and symptom feigning: scale refinement

The F(p) scale of the MMPI-2 is widely used to help identify exaggeration of psychological problems in psychiatric, forensic, and neuropsychological settings. The scale was constructed by selecting all MMPI-2 items (N = 27) that were endorsed by less than 20% of a sample of VA psychiatric inpatients and 20% of the normative sample used in restandardizing the MMPI-2. Although F(p) is used to measure symptom exaggeration and malingering, 4 of its 27 items load on the Lie (L) scale, which is known to be a measure of defensiveness and symptom underreporting. These four items, which express a denial of occasional anger, irritability, and procrastination, could conceivably measure an uncommon expression of defensiveness. This study used 150 neuropsychological referrals to test the hypotheses that (a) the four L scale items measure defensiveness, not exaggeration, and (b) the elimination of these items improves the utility of F(p) in assessing symptom exaggeration. The results indicate that the four L scale items are associated with defensiveness, not with symptom exaggeration. One third of the patients had an average T-score artifact of 9.5 points on F(p) as a result of endorsing these L scale items, with a range of 0T to 21T. Using the K scale as a criterion for level of problem disclosure, a shortened version of F(p) (omitting the four L scale items) was superior to F(p) as a measure of symptom exaggeration (r = -.46 vs. -.36, r2 = 21% vs. 13% of the variance). The implications for clinical practice are discussed.