- Email: [email protected]
The relationship between measures of psychopathology, intelligence, and memory among adults seen for psychoeducational assessment
Archives of Clinical Neuropsychology 21 (2006) 297–301
The relationship between measures of psychopathology, intelligence, and memory among adults seen for psychoeducational assessment Benjamin J. Morasco a,∗ , Jeffrey D. Gfeller b , John T. Chibnall b a
Department of Behavioral Health and Clinical Neurosciences, Portland VA Medical Center, 3710 SW U.S. Veterans Hospital Road (P3MHDC), Portland, OR 97239, USA b Saint Louis University, USA Accepted 30 March 2006
Abstract This study assessed the relationship between symptoms of psychopathology and cognitive functioning in clients completing comprehensive psychoeducational assessments at a university-based outpatient mental health clinic. Seventy clients (36 women, 34 men, mean age = 28.8) completed the Wechsler Memory Scale – Third Edition (WMS-III), Wechsler Adult Intelligence Scale – Third Edition (WAIS-III), and Minnesota Multiphasic Personality Inventory – Second Edition (MMPI-2). Partial correlations between the MMPI-2 clinical scales, WMS-III Index scores, WAIS-III Index scores, and WAIS-III IQ scores were not significant. Memory and Intelligence scores for clients with comorbid symptoms of depression and anxiety were comparable to scores for clients without comorbid symptomatology. Psychopathology factors accounted for 22% of the variance in the WAIS-III Full Scale IQ and 6.5% of the variance in the WMS-III General Memory Index. The results suggest that psychopathology as measured by the MMPI-2 may be minimally associated with intelligence and memory test performance in adults seen for psychoeducational assessment. © 2006 National Academy of Neuropsychology. Published by Elsevier Ltd. All rights reserved. Keywords: Cognitive functioning; Depression; MMPI-2; WMS-III; WAIS-III; Assessment
1. Introduction Prior research has identified a significant relationship between psychopathology and cognitive impairment (Burt, Zembar, & Niederehe, 1995; Kindermann & Brown, 1997), such that some psychological disorders are associated with lower cognitive functioning. However, prior research has been limited, as few studies have examined the relationship between psychopathology and cognitive functioning among clients with a history of head injury, or some other factor possibly impacting neurological functioning (Christensen, Griffiths, MacKinnon, & Jacomb, 1997). Conversely, Rohling, Green, Allen, and Iverson (2002) assessed the relationship between depressive symptoms and cognitive functioning among 420 outpatients evaluated in a medicolegal context. They found no association between symptoms of depression and neuropsychological or psychomotor performance. These results were supported by Tsushima, Johnson, Lee, Matsukawa, and Fast (2005) in a study of 60 patients presenting for coronary artery bypass graft surgery, who also found no association between affective symptoms and cognitive functioning.
∗
Corresponding author. E-mail address: [email protected] (B.J. Morasco).
0887-6177/$ – see front matter © 2006 National Academy of Neuropsychology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.acn.2006.03.005
298
B.J. Morasco et al. / Archives of Clinical Neuropsychology 21 (2006) 297–301
The current study expanded on prior research by examining the relationships between self-reported symptoms of psychopathology (as measured by the MMPI-2) and performance on tests of memory and intellectual functioning in an outpatient sample. The relationship between intellectual functioning and psychopathology has received little empirical attention, perhaps because a portion of the subtests that comprise intelligence assess overlearned information (Horn & Cattell, 1966), an area that research indicates is not associated with psychiatric symptoms. Based on recent findings from Kizilbash, Vanderploeg, and Curtiss (2002), who found that comorbid symptoms of depression and anxiety impact cognitive functioning to a greater degree than symptoms of either disorder alone, we also examined cognitive functioning in adults with self-reported symptoms of depression and anxiety. Finally, we sought to replicate the finding that psychological factors accounted for a significant percentage of the variance in memory functioning (Ross, Putnam, Gass, & Adams, 2003). Based on this research, it was hypothesized that (1) MMPI-2 clinical scales would correlate with memory and intelligence scores, (2) participants with elevations on measures of depression and anxiety would exhibit lower performance on cognitive tasks compared to participants without dual elevations, and (3) MMPI-2 clinical scales would account for a significant percentage of the variance in measures of memory and intellectual functioning. 2. Method Between January 1999 and December 2002, 87 individuals completed the Minnesota Multiphasic Personality Inventory – Second Edition (MMPI-2; Butcher et al., 1989), Wechsler Adult Intelligence Scale – Third Edition (WAISIII; Wechsler, 1997a), and Wechsler Memory Scale – Third Edition (WMS-III; Wechsler, 1997b) at a university-based outpatient mental health clinic. Participants were included in this study if they completed the above measures, were at least 18 years old at the time of the evaluation, and spoke English as a first language. To increase external validity, no one was excluded on the basis of other demographic or psychosocial characteristics. Seventeen individuals (19.5%) were excluded due to invalid MMPI-2 protocols. MMPI-2 validity criteria were drawn from Gass (1996) and modified with recommendations outlined in Graham (2000). In this study, MMPI-2 profiles met all of the following validity criteria: less than 30 item omissions, L scale ≤ 65, F scale ≤ 100, K scale ≤ 65, F(b) scale ≤ 100, VRIN T score ≤ 80, TRIN T score ≤ 80, and F-K raw score ≤ 11. The study sample included 36 women (51.4%) and 34 men (48.6%), with a mean age of 28.8 years (S.D. = 11.0). Mean years of education was 13.9 (S.D. = 2.0). The sample was predominantly Caucasian (n = 63, 90.0%). Most participants were full- or part-time college students (n = 51, 72.9%), 14 participants (20.0%) were working full-time, and the remaining five participants were not employed, receiving disability, or retired. Regarding referral questions, 11 participants (15.7%) were referred to the clinic due to academic difficulties, 49 (70.0%) for evaluation of a learning disorder and/or attention deficit-hyperactivity disorder (ADHD), three (4.3%) for a psychiatric differential diagnosis, and four (5.7%) for a neuropsychological evaluation (specific referral data were missing for three participants). Most participants had a history of outpatient psychological treatment (n = 48, 68.6%), 24 (34.3%) were currently taking a psychotropic medication, and 11 (15.7%) reported a prior history of inpatient psychiatric care. All participants underwent comprehensive psychological evaluations (completing at least the MMPI-2, WMSIII, and WAIS-III). The primary diagnoses given during these evaluations included learning disorders (n = 38, 54.3%), anxiety disorders (n = 27, 38.6%), depressive disorders (n = 20, 28.6%), and ADHD (n = 15, 21.4%). Of the participants that met criteria for an axis I disorder, 36 (60.0%) were diagnosed with a comorbid disorder. In general, the sample exhibited minimal pathology on the MMPI-2, as none of the mean clinical or content scales exceeded the level for clinical significance (i.e., T score ≥ 65). Eighteen participants (25.7%) had T scores ≥ 65 on scale 2, 26 (37.1%) had an elevated scale 7, and 15 participants (21.4%) had clinically significant elevations on scales 2 and 7. 3. Results Partial correlations, controlling for education and ethnicity, were computed between the clinical scales of the MMPI2 and the Index and Intelligence scores of the WMS-III and WAIS-III. With N = 70, the power of these analyses was 0.80 for correlations of approximately r = 0.33 (11% shared variance), assuming non-directional tests and alpha = 0.05 (Jaccard & Becker, 1990). Only one significant correlation emerged, between MMPI-2 scale 7 and the Processing Speed Index of the WAIS-III (r = 0.25, p < 0.05). However, with adjustment for multiple comparisons (p < 0.003), none of the correlations were significant.
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Fig. 1. Mean WAIS-III IQ and Index scores of participants with elevations on scales 2 and 7 of the MMPI-2 compared with participants without clinically significant elevations on these scales. Note. Group scores were not significantly different (p < 0.05) on any of the WAIS-III IQ or Index scores. VIQ = Verbal Intelligence. PIQ = Performance Intelligence. FSIQ = Full Scale Intelligence. VCI = Verbal Comprehension Index. POI = Perceptual Organization Index. WMI = Working Memory Index. PSI = Processing Speed Index.
A one-way MANOVA was utilized to compare the WAIS-III IQ and Index scores of participants with clinically significant elevations on MMPI-2 clinical scales 2 and 7 (measures of depression and anxiety) versus clients without clinically significant elevations on both scales. As previously indicated, 15 participants (21.4%) had dual elevations while 52 (74.3%) did not have elevations on both scales. With 15 participants in the smaller group, the power of this analysis for each dependent variable was 0.80 for effect sizes of approximately eta2 = 0.22, assuming alpha = 0.05. Here, eta2 indicates the proportion of variance explained in a dependent variable as a function of group designation. By convention, eta2 values on the order of 0.22 constitute a moderate effect (Jaccard & Becker, 1990). The MANOVA was not significant (Wilks’ lambda = 0.92, F(7, 57) = 0.71, p = 0.66, partial eta2 = 0.08, observed power = 0.28). Similarly, WMS-III Index scores were not significantly different between the two groups (Wilks’ lambda = 0.81, F(8, 57) = 1.60, p = 0.15, partial eta2 = 0.19, observed power = 0.64). Figs. 1 and 2 display the mean intelligence and memory scores for both groups. Although none of the differences were statistically significant, there was a trend towards higher performance on all the WAIS-III Intelligence and Index scores and five of eight WMS-III Index scores for participants who had clinically significant elevations on scales 2 and 7 of the MMPI-2. A true stepwise multiple regression was used to predict intellectual functioning from MMPI-2 clinical and content scores. With N = 70, this analysis was potentially unstable due to the fact that, with stepwise regression, inclusion of variables in the final equation is based on statistical criteria, such that even small differences in associations across samples – the likelihood of which is inflated in inverse proportion to sample size – can have substantial influence on the entry of predictors into the model (Tabachnick & Fidell, 1996). This analysis was adequately powered for moderate effect sizes on the order of R2 = 0.15. MMPI-2 variables accounted for 22% (F(3, 66) = 6.33, p < 0.001) of the variance in the Full Scale IQ (FSIQ) score of the WAIS-III. The final model included three content scales; Anxiety was positively
Fig. 2. Mean WMS-III Index scores of participants with elevations on scales 2 and 7 of the MMPI-2 compared with participants without clinically significant elevations on these scales. Note. Group scores were not significantly different (p < 0.05) on any of the WMS-III Index scores. Aud Immed = Auditory Immediate Index. Vis Immed = Visual Immediate Index. Immed Mem = Immediate Memory Index. Aud Del = Auditory Delayed Index. Vis Del = Visual Delayed Index. Aud Rec = Auditory Recognition Delayed Index. Gen Mem = General Memory Index. Work Mem = Working Memory Index.
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associated, while Obsessiveness and Antisocial Practices were negatively associated with the FSIQ scores. A second stepwise regression analysis was performed to predict memory performance from MMPI-2 scales. Only one content scale (Antisocial Practices) entered the model, was negatively associated, and accounted for 6.5% (F(1, 68) = 4.73, p < 0.05) of the variance in the General Memory Index of the WMS-III. 4. Discussion This study found relatively modest and primarily non-significant relationships between symptoms of psychopathology, intellectual abilities, and memory functioning. Results from this study, combined with the recent research (Rohling et al., 2002; Tsushima et al., 2005), suggest that symptoms of psychopathology may be minimally associated with cognitive functioning in clients with a history of mild neurological compromise. However, characteristics of the research methodology may help to explain why these results differ from some prior studies. Similar to Rohling et al. (2002), participants who provided invalid effort were excluded from the analyses. It is possible that the finding of an association between psychopathology and cognitive functioning identified in prior studies may be due to the inclusion of participants who provided invalid self-report regarding psychopathology. In addition, the current study employed commonly used standardized neuropsychological measures in the assessment of cognitive functioning, rather than assessment with a single subtest, dated measures, or non-standardized tests. Characteristics specific to this sample may limit the generalizability of these findings. For example, this study did not include participants with schizophrenia, which has been shown to be clearly associated with cognitive functioning (Kolb & Whishaw, 1983). Thus, the finding of a lack of association between psychopathology and cognitive functioning may be related only to outpatients with depressive or anxiety symptomatology. Second, this sample as a group did not display significant pathology on the MMPI-2. Prior investigations that identified an association between psychopathology and cognitive functioning indicated that the severity of the mental disorder, rather than the presence of symptoms alone, may account for a greater percentage of the variance in cognitive functioning (Burt et al., 1995; Christensen et al., 1997). Third, many participants were diagnosed with a Learning Disorder (54.3%) or ADHD (21.4%). Persons with Learning Disorders and ADHD often perform less well on certain cognitive indices, such as Processing Speed and Working Memory (Wechsler, 1997c). The confounding effects of these conditions in some of the participants may have contributed to the lack of association between psychopathology and cognitive performance in this study. There also exist limitations to this study that may have contributed to the lack of significant findings. The sample size limited the ability to detect significant differences to effect sizes of low strength. For example, a review of the eta2 and observed power for the MANOVA comparing the memory functioning of participants with elevations on MMPI-2 scales 2 and 7 versus clients without significant elevations suggests that this test may have been significant, had there been an adequate number of subjects. The trend in this test was also contrary to study hypotheses and prior literature, which suggests the possibility of a significant covariate. The multiple regression results should be interpreted with caution, as the small sample size and stepwise regression method combine to create potential instability in the final model. However, this procedure is consistent with prior literature (Gass, 1996; Ross et al., 2003; Tsushima et al., 2005). Finally, there exist other potential moderators of the associations examined in this study that were not measured or controlled for in the analyses, including previous psychiatric history, socioeconomic status, history of neurological insult, alcohol consumption, or other factors. Despite these limitations, this study has significant implications. The results suggest a weak relationship between symptoms of psychopathology and cognitive functioning in clients presenting for psychoeducational assessment. Neuropsychologists who assess cognitive functioning are encouraged to explore reasons other than psychopathology to explain deficits, particularly when evaluating clients with a mood or affective disorder. It is likely that other factors (e.g., history of a head injury, diagnosis of a learning disorder or ADHD) impact cognitive functioning to a greater extent than psychopathology. Acknowledgments The authors gratefully acknowledge Lauren Schwarz, Dr. Donna LaVoie, and Dr. Katherine Elder for their assistance with this work. We also appreciate the comments from the editor and two anonymous reviewers on a prior draft of this manuscript.
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References Burt, D. B., Zembar, M. J., & Niederehe, G. (1995). Depression and memory impairment: A meta-analysis of the association, its pattern, and specificity. Psychological Bulletin, 117, 285–305. Butcher, J. N., Dahlstrom, W. G., Graham, J. R., Tellegen, A., & Kaemmer, B. (1989). Minnesota Multiphasic Personality Inventory-2 (MMPI-2): Manual for administration and scoring. Minneapolis: University of Minnesota Press. Christensen, H., Griffiths, K., MacKinnon, A., & Jacomb, P. (1997). A quantitative review of cognitive deficits in depression and Alzheimer-type dementia. Journal of the International Neuropsychological Society, 3, 631–651. Gass, C. S. (1996). MMPI-2 variables in attention and memory test performance. Psychological Assessment, 8, 135–138. Graham, J. R. (2000). MMPI-2: Assessing personality and psychopathology (3rd ed.). New York: Oxford University Press. Horn, J. L., & Cattell, R. B. (1966). Refinement and test of theory of fluid and crystallized intelligence. Journal of Educational Pscyhology, 57, 253–270. Jaccard, J., & Becker, M. A. (1990). Statistics for the behavioral sciences (2nd ed.). Belmont, CA: Wadsworth Publishing Company. Kindermann, S. S., & Brown, G. G. (1997). Depression and memory in the elderly: A meta-analysis. Journal of Clinical and Experimental Neuropsychology, 19, 625–642. Kizilbash, A. H., Vanderploeg, R. D., & Curtiss, G. (2002). The effects of depression and anxiety on memory performance. Archives of Clinical Neuropsychology, 17, 57–67. Kolb, B., & Whishaw, I. Q. (1983). Performance of schizophrenic patients on tests sensitive to left or right frontal, temporal, or parietal function in neurological patients. Journal of Nervous and Mental Disease, 171, 435–443. Rohling, M. L., Green, P., Allen, L. M., & Iverson, G. L. (2002). Depressive symptoms and neurocognitive test scores in patients passing symptom validity tests. Archives of Clinical Neuropsychology, 17, 205–222. Ross, S. R., Putnam, S. H., Gass, C. S., Bailey, D. E., & Adams, K. M. (2003). MMPI-2 indices of psychological disturbance and attention and memory test performance in head injury. Archives of Clinical Neuropsychology, 18, 905–916. Tabachnick, B. G., & Fidell, L. S. (1996). Using multivariate statistics (3rd ed.). New York: HarperCollins College Publishers. Tsushima, W. T., Johnson, D. B., Lee, J. D., Matsukawa, J. M., & Fast, K. M. S. (2005). Depression, anxiety and neuropsychological test scores of candidates for coronary artery bypass graft surgery. Archives of Clinical Neuropsychology, 20, 667–673. Wechsler, D. (1997a). WAIS-III administration and scoring manual. San Antonio, TX: Psychological Corporation. Wechsler, D. (1997b). Wechsler Memory Scale – third edition: Administration and scoring manual. San Antonio, TX: Psychological Corporation. Wechsler, D. (1997c). Wais-III/WMS-III technical manual. San Antonio, TX: Psychological Corporation.
The relationship between measures of psychopathology, intelligence, and memory among adults seen for psychoeducational assessment Benjamin J. Morasco a,∗ , Jeffrey D. Gfeller b , John T. Chibnall b a
Department of Behavioral Health and Clinical Neurosciences, Portland VA Medical Center, 3710 SW U.S. Veterans Hospital Road (P3MHDC), Portland, OR 97239, USA b Saint Louis University, USA Accepted 30 March 2006
Abstract This study assessed the relationship between symptoms of psychopathology and cognitive functioning in clients completing comprehensive psychoeducational assessments at a university-based outpatient mental health clinic. Seventy clients (36 women, 34 men, mean age = 28.8) completed the Wechsler Memory Scale – Third Edition (WMS-III), Wechsler Adult Intelligence Scale – Third Edition (WAIS-III), and Minnesota Multiphasic Personality Inventory – Second Edition (MMPI-2). Partial correlations between the MMPI-2 clinical scales, WMS-III Index scores, WAIS-III Index scores, and WAIS-III IQ scores were not significant. Memory and Intelligence scores for clients with comorbid symptoms of depression and anxiety were comparable to scores for clients without comorbid symptomatology. Psychopathology factors accounted for 22% of the variance in the WAIS-III Full Scale IQ and 6.5% of the variance in the WMS-III General Memory Index. The results suggest that psychopathology as measured by the MMPI-2 may be minimally associated with intelligence and memory test performance in adults seen for psychoeducational assessment. © 2006 National Academy of Neuropsychology. Published by Elsevier Ltd. All rights reserved. Keywords: Cognitive functioning; Depression; MMPI-2; WMS-III; WAIS-III; Assessment
1. Introduction Prior research has identified a significant relationship between psychopathology and cognitive impairment (Burt, Zembar, & Niederehe, 1995; Kindermann & Brown, 1997), such that some psychological disorders are associated with lower cognitive functioning. However, prior research has been limited, as few studies have examined the relationship between psychopathology and cognitive functioning among clients with a history of head injury, or some other factor possibly impacting neurological functioning (Christensen, Griffiths, MacKinnon, & Jacomb, 1997). Conversely, Rohling, Green, Allen, and Iverson (2002) assessed the relationship between depressive symptoms and cognitive functioning among 420 outpatients evaluated in a medicolegal context. They found no association between symptoms of depression and neuropsychological or psychomotor performance. These results were supported by Tsushima, Johnson, Lee, Matsukawa, and Fast (2005) in a study of 60 patients presenting for coronary artery bypass graft surgery, who also found no association between affective symptoms and cognitive functioning.
∗
Corresponding author. E-mail address: [email protected] (B.J. Morasco).
0887-6177/$ – see front matter © 2006 National Academy of Neuropsychology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.acn.2006.03.005
298
B.J. Morasco et al. / Archives of Clinical Neuropsychology 21 (2006) 297–301
The current study expanded on prior research by examining the relationships between self-reported symptoms of psychopathology (as measured by the MMPI-2) and performance on tests of memory and intellectual functioning in an outpatient sample. The relationship between intellectual functioning and psychopathology has received little empirical attention, perhaps because a portion of the subtests that comprise intelligence assess overlearned information (Horn & Cattell, 1966), an area that research indicates is not associated with psychiatric symptoms. Based on recent findings from Kizilbash, Vanderploeg, and Curtiss (2002), who found that comorbid symptoms of depression and anxiety impact cognitive functioning to a greater degree than symptoms of either disorder alone, we also examined cognitive functioning in adults with self-reported symptoms of depression and anxiety. Finally, we sought to replicate the finding that psychological factors accounted for a significant percentage of the variance in memory functioning (Ross, Putnam, Gass, & Adams, 2003). Based on this research, it was hypothesized that (1) MMPI-2 clinical scales would correlate with memory and intelligence scores, (2) participants with elevations on measures of depression and anxiety would exhibit lower performance on cognitive tasks compared to participants without dual elevations, and (3) MMPI-2 clinical scales would account for a significant percentage of the variance in measures of memory and intellectual functioning. 2. Method Between January 1999 and December 2002, 87 individuals completed the Minnesota Multiphasic Personality Inventory – Second Edition (MMPI-2; Butcher et al., 1989), Wechsler Adult Intelligence Scale – Third Edition (WAISIII; Wechsler, 1997a), and Wechsler Memory Scale – Third Edition (WMS-III; Wechsler, 1997b) at a university-based outpatient mental health clinic. Participants were included in this study if they completed the above measures, were at least 18 years old at the time of the evaluation, and spoke English as a first language. To increase external validity, no one was excluded on the basis of other demographic or psychosocial characteristics. Seventeen individuals (19.5%) were excluded due to invalid MMPI-2 protocols. MMPI-2 validity criteria were drawn from Gass (1996) and modified with recommendations outlined in Graham (2000). In this study, MMPI-2 profiles met all of the following validity criteria: less than 30 item omissions, L scale ≤ 65, F scale ≤ 100, K scale ≤ 65, F(b) scale ≤ 100, VRIN T score ≤ 80, TRIN T score ≤ 80, and F-K raw score ≤ 11. The study sample included 36 women (51.4%) and 34 men (48.6%), with a mean age of 28.8 years (S.D. = 11.0). Mean years of education was 13.9 (S.D. = 2.0). The sample was predominantly Caucasian (n = 63, 90.0%). Most participants were full- or part-time college students (n = 51, 72.9%), 14 participants (20.0%) were working full-time, and the remaining five participants were not employed, receiving disability, or retired. Regarding referral questions, 11 participants (15.7%) were referred to the clinic due to academic difficulties, 49 (70.0%) for evaluation of a learning disorder and/or attention deficit-hyperactivity disorder (ADHD), three (4.3%) for a psychiatric differential diagnosis, and four (5.7%) for a neuropsychological evaluation (specific referral data were missing for three participants). Most participants had a history of outpatient psychological treatment (n = 48, 68.6%), 24 (34.3%) were currently taking a psychotropic medication, and 11 (15.7%) reported a prior history of inpatient psychiatric care. All participants underwent comprehensive psychological evaluations (completing at least the MMPI-2, WMSIII, and WAIS-III). The primary diagnoses given during these evaluations included learning disorders (n = 38, 54.3%), anxiety disorders (n = 27, 38.6%), depressive disorders (n = 20, 28.6%), and ADHD (n = 15, 21.4%). Of the participants that met criteria for an axis I disorder, 36 (60.0%) were diagnosed with a comorbid disorder. In general, the sample exhibited minimal pathology on the MMPI-2, as none of the mean clinical or content scales exceeded the level for clinical significance (i.e., T score ≥ 65). Eighteen participants (25.7%) had T scores ≥ 65 on scale 2, 26 (37.1%) had an elevated scale 7, and 15 participants (21.4%) had clinically significant elevations on scales 2 and 7. 3. Results Partial correlations, controlling for education and ethnicity, were computed between the clinical scales of the MMPI2 and the Index and Intelligence scores of the WMS-III and WAIS-III. With N = 70, the power of these analyses was 0.80 for correlations of approximately r = 0.33 (11% shared variance), assuming non-directional tests and alpha = 0.05 (Jaccard & Becker, 1990). Only one significant correlation emerged, between MMPI-2 scale 7 and the Processing Speed Index of the WAIS-III (r = 0.25, p < 0.05). However, with adjustment for multiple comparisons (p < 0.003), none of the correlations were significant.
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Fig. 1. Mean WAIS-III IQ and Index scores of participants with elevations on scales 2 and 7 of the MMPI-2 compared with participants without clinically significant elevations on these scales. Note. Group scores were not significantly different (p < 0.05) on any of the WAIS-III IQ or Index scores. VIQ = Verbal Intelligence. PIQ = Performance Intelligence. FSIQ = Full Scale Intelligence. VCI = Verbal Comprehension Index. POI = Perceptual Organization Index. WMI = Working Memory Index. PSI = Processing Speed Index.
A one-way MANOVA was utilized to compare the WAIS-III IQ and Index scores of participants with clinically significant elevations on MMPI-2 clinical scales 2 and 7 (measures of depression and anxiety) versus clients without clinically significant elevations on both scales. As previously indicated, 15 participants (21.4%) had dual elevations while 52 (74.3%) did not have elevations on both scales. With 15 participants in the smaller group, the power of this analysis for each dependent variable was 0.80 for effect sizes of approximately eta2 = 0.22, assuming alpha = 0.05. Here, eta2 indicates the proportion of variance explained in a dependent variable as a function of group designation. By convention, eta2 values on the order of 0.22 constitute a moderate effect (Jaccard & Becker, 1990). The MANOVA was not significant (Wilks’ lambda = 0.92, F(7, 57) = 0.71, p = 0.66, partial eta2 = 0.08, observed power = 0.28). Similarly, WMS-III Index scores were not significantly different between the two groups (Wilks’ lambda = 0.81, F(8, 57) = 1.60, p = 0.15, partial eta2 = 0.19, observed power = 0.64). Figs. 1 and 2 display the mean intelligence and memory scores for both groups. Although none of the differences were statistically significant, there was a trend towards higher performance on all the WAIS-III Intelligence and Index scores and five of eight WMS-III Index scores for participants who had clinically significant elevations on scales 2 and 7 of the MMPI-2. A true stepwise multiple regression was used to predict intellectual functioning from MMPI-2 clinical and content scores. With N = 70, this analysis was potentially unstable due to the fact that, with stepwise regression, inclusion of variables in the final equation is based on statistical criteria, such that even small differences in associations across samples – the likelihood of which is inflated in inverse proportion to sample size – can have substantial influence on the entry of predictors into the model (Tabachnick & Fidell, 1996). This analysis was adequately powered for moderate effect sizes on the order of R2 = 0.15. MMPI-2 variables accounted for 22% (F(3, 66) = 6.33, p < 0.001) of the variance in the Full Scale IQ (FSIQ) score of the WAIS-III. The final model included three content scales; Anxiety was positively
Fig. 2. Mean WMS-III Index scores of participants with elevations on scales 2 and 7 of the MMPI-2 compared with participants without clinically significant elevations on these scales. Note. Group scores were not significantly different (p < 0.05) on any of the WMS-III Index scores. Aud Immed = Auditory Immediate Index. Vis Immed = Visual Immediate Index. Immed Mem = Immediate Memory Index. Aud Del = Auditory Delayed Index. Vis Del = Visual Delayed Index. Aud Rec = Auditory Recognition Delayed Index. Gen Mem = General Memory Index. Work Mem = Working Memory Index.
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associated, while Obsessiveness and Antisocial Practices were negatively associated with the FSIQ scores. A second stepwise regression analysis was performed to predict memory performance from MMPI-2 scales. Only one content scale (Antisocial Practices) entered the model, was negatively associated, and accounted for 6.5% (F(1, 68) = 4.73, p < 0.05) of the variance in the General Memory Index of the WMS-III. 4. Discussion This study found relatively modest and primarily non-significant relationships between symptoms of psychopathology, intellectual abilities, and memory functioning. Results from this study, combined with the recent research (Rohling et al., 2002; Tsushima et al., 2005), suggest that symptoms of psychopathology may be minimally associated with cognitive functioning in clients with a history of mild neurological compromise. However, characteristics of the research methodology may help to explain why these results differ from some prior studies. Similar to Rohling et al. (2002), participants who provided invalid effort were excluded from the analyses. It is possible that the finding of an association between psychopathology and cognitive functioning identified in prior studies may be due to the inclusion of participants who provided invalid self-report regarding psychopathology. In addition, the current study employed commonly used standardized neuropsychological measures in the assessment of cognitive functioning, rather than assessment with a single subtest, dated measures, or non-standardized tests. Characteristics specific to this sample may limit the generalizability of these findings. For example, this study did not include participants with schizophrenia, which has been shown to be clearly associated with cognitive functioning (Kolb & Whishaw, 1983). Thus, the finding of a lack of association between psychopathology and cognitive functioning may be related only to outpatients with depressive or anxiety symptomatology. Second, this sample as a group did not display significant pathology on the MMPI-2. Prior investigations that identified an association between psychopathology and cognitive functioning indicated that the severity of the mental disorder, rather than the presence of symptoms alone, may account for a greater percentage of the variance in cognitive functioning (Burt et al., 1995; Christensen et al., 1997). Third, many participants were diagnosed with a Learning Disorder (54.3%) or ADHD (21.4%). Persons with Learning Disorders and ADHD often perform less well on certain cognitive indices, such as Processing Speed and Working Memory (Wechsler, 1997c). The confounding effects of these conditions in some of the participants may have contributed to the lack of association between psychopathology and cognitive performance in this study. There also exist limitations to this study that may have contributed to the lack of significant findings. The sample size limited the ability to detect significant differences to effect sizes of low strength. For example, a review of the eta2 and observed power for the MANOVA comparing the memory functioning of participants with elevations on MMPI-2 scales 2 and 7 versus clients without significant elevations suggests that this test may have been significant, had there been an adequate number of subjects. The trend in this test was also contrary to study hypotheses and prior literature, which suggests the possibility of a significant covariate. The multiple regression results should be interpreted with caution, as the small sample size and stepwise regression method combine to create potential instability in the final model. However, this procedure is consistent with prior literature (Gass, 1996; Ross et al., 2003; Tsushima et al., 2005). Finally, there exist other potential moderators of the associations examined in this study that were not measured or controlled for in the analyses, including previous psychiatric history, socioeconomic status, history of neurological insult, alcohol consumption, or other factors. Despite these limitations, this study has significant implications. The results suggest a weak relationship between symptoms of psychopathology and cognitive functioning in clients presenting for psychoeducational assessment. Neuropsychologists who assess cognitive functioning are encouraged to explore reasons other than psychopathology to explain deficits, particularly when evaluating clients with a mood or affective disorder. It is likely that other factors (e.g., history of a head injury, diagnosis of a learning disorder or ADHD) impact cognitive functioning to a greater extent than psychopathology. Acknowledgments The authors gratefully acknowledge Lauren Schwarz, Dr. Donna LaVoie, and Dr. Katherine Elder for their assistance with this work. We also appreciate the comments from the editor and two anonymous reviewers on a prior draft of this manuscript.
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