The Schizophrenia Proneness (SzP) Scale: An MMPI-2 Measure of Schizophrenia Liability

Transcription

1 The Schizophrenia Proneness (SzP) Scale: An MMPI-2 Measure of Schizophrenia Liability P. Kevin Bolinskey Medical College of Virginia Irving I. Gottesman University of Minnesota David S. Nichols Pacific University We examined the psychometric properties and construct validity for a Minnesota Multiphasic Personality Inventory 2 Schizophrenia Proneness (SzP) scale (Bolinskey et al., 2001) and provided normative statistics. Premorbid participants were offspring of parents with schizophreniarelated illness (SRI), with comparison groups of offspring of parents with major affective disorders and offspring of normals. Postmorbid participants were twins affected with SRI; their unaffected relatives served as a comparison group. Results suggest that an SzP T score of 65 or above is an effective indicator of personality processes associated with increased liability to developing SRI Wiley Periodicals, Inc. J Clin Psychol 59: , Keywords: endophenotype; construct validity; offspring of schizophrenics; twins The authors would like to thank L. Erlenmeyer-Kimling, of the New York State Psychiatric Institute and Columbia University, for allowing access to the New York High-Risk Project data; W. Grant Dahlstrom of the University of North Carolina at Chapel Hill for providing access to the MMPI-2 normative group data; and Alastair Cardno for providing diagnostic data for each of the Maudsley twins. We would also like to thank James N. Butcher, Robert P. Archer, and Randolph C. Arnau for their comments and suggestions on an earlier version of this report. This work was supported in part by NIMH Training Grant MH (P. Kevin Bolinskey). Correspondence concerning this article should be addressed to: P. Kevin Bolinskey, Virginia Institute of Psychiatric and Behavioral Genetics, 800 East Leigh Street, Suite 1, P.O. Box , Medical College of Virginia, Richmond, VA ; pkbolinskey@vcu.edu. JOURNAL OF CLINICAL PSYCHOLOGY, Vol. 59(9), (2003) 2003 Wiley Periodicals, Inc. Published online in Wiley InterScience ( DOI: /jclp.10187

2 1032 Journal of Clinical Psychology, September 2003 A primary goal of recent research has been to identify Minnesota Multiphasic Personality Inventory (MMPI) based indicators of liability to developing schizophrenia, and its related disorders, before the clinical onset of the disorder (cf. Carter, Parnas, Cannon, Schulsinger, & Mednick, 1999; Moldin, Gottesman, Erlenmeyer-Kimling, & Cornblatt, 1990). Partly on the basis of the results of these prior studies, Bolinskey et al. (2001) introduced a preliminary version of the Schizophrenia Proneness (SzP; see Appendix) scale, which was derived from a subset of items in Rosen s (1962) Paranoid Schizophrenia (Pz) scale. Specifically, SzP contains those items from Pz that are unshared with Wiggins s (1966) Psychoticism (PSY) scale. Rationale for the derivation of the scale is described fully in our previous study. Initial analyses of the scale s effectiveness in discriminating individuals who later experienced the onset of schizophrenia were performed using raw scale scores. The purpose of the present study is to provide normative statistics for a revised version of the scale, as well as to provide further validity information. The revised version of SzP is a 32-item scale composed of the unique (nonshared with PSY) items of Pz in the MMPI-2 (Butcher et al., 2001). The scale shares some items with the basic clinical and validity scales; Table 1 provides a summary of shared items and item intercorrelations between SzP and the basic MMPI-2 validity and clinical scales. SzP shares more items with scales F, Sc, and Si than with the other basic scales (8, 10, and 6 items, respectively). The item intercorrelations between SzP and the basic scales are modest, ranging from.00 (L and K )to.20(sc). The observed correlations between SzP and the traditional validity scales L, F, and K suggest that SzP scores may be relatively resistant to response biases, such as may be adopted to exaggerate or minimize psychological disturbance. With the removal of items with obvious psychotic content from Pz, it was hypothesized that SzP should reflect only liability (i.e., predisposition) to schizophrenia-related illness (SRI), without a redundancy with overt psychotic symptomatology. Initial results in a high-risk design appeared promising. Those participants who later developed SRI scored significantly higher on the scale than those who did not, although the latter group included participants who later developed a full range of other psychiatric disorders Table 1 Number of Shared Items With Scoring Direction and Item Intercorrelations for MMPI-2 Basic Clinical and Validity Scales and Schizophrenia Proneness (SzP) MMPI-2 Scale Number of Items in Scale Items Scored in Same Direction Items Scored in Opposite Direction Item Intercorrelation L (Lie) F (Infrequency) K (Correction) (Hypochondriasis) (Depression) (Hysteria) (Psychopathic Deviate) (Paranoia) (Psychasthenia) (Schizophrenia) (Mania) (Social Introversion) Note. SzP contains 32 items. MMPI-2 Minnesota Multiphasic Personality Inventory 2.

3 The Schizophrenia Proneness Scale 1033 (e.g., mania, depression, antisocial personality disorder, substance abuse); furthermore, a raw cutoff score of 15 was found to be effective in discriminating between those who developed SRI and those who did not, with an accuracy rate of 92% (Bolinskey et al., 2001). The goals of the present report are twofold: (a) to provide normative statistics for an MMPI-2 (Butcher et al., 2001) version of SzP and (b) to examine the construct validity and effectiveness of SzP as an indicator of liability to developing SRI. Given the breadth of these two goals, the methodology and results for each part of the study are presented separately, with the normative process described in the Standardization section and validity estimations presented in the Effectiveness Evaluation section, followed by a general discussion. Method Standardization Participants. The MMPI-2 normative sample (Butcher et al., 2001) served as the standardization group for this portion of the study. This group has been fully described elsewhere (cf. Greene, 2000). Briefly, this sample consists of 1,462 females with a mean age of 40.5 (SD 15.2) and 1,138 males with a mean age of 41.7 (SD 15.3). Design and Procedures. As the preliminary version of SzP (Bolinskey et al., 2001) contained some items that do not appear in the MMPI-2, a revised version of the scale containing only those items appearing on the MMPI-2 was scored for the present analysis. Each step of the normative process was performed separately for females and males. In order to achieve percentile equivalence among MMPI-2 scales showing substantial, but varying, positive skew, scaled scores for the basic clinical scales (1 4, 6 9), as well as the content and content-component scales, are represented as uniform T scores (Tellegen & Ben-Porath, 1992). Because female and male distributions of SzP revealed similar positive skew, and to facilitate percentile representations of scores on this scale, a decision was made to follow this method of obtaining T scores for SzP. Uniform T scores are based on polynomial regression equations and are calculated using Equation 1: T b 0 b 1 x b 2 d 2 b 3 d 3 where x is the obtained raw score; b 0 is an intercept; b 1, b 2, and b 3 are regression weights; and d equals c x (if x c), where c is the raw score equivalent to a linear T score of 60. If x c, d 0. As can be seen from Equation 1, the quadratic and cubic terms have no effect on T scores above 60; their only function is to normalize the distribution of obtained T scores below 60. Linear T scores were first calculated so that c could be estimated. Next, estimated raw scores for critical percentile rankings (see Tellegen & Ben-Porath, 1992) in the normative group were calculated, and these estimated raw scores were matched with the corresponding uniform T score for their respective percentile ranking. Quadratic and cubic terms (d 2 and d 3, respectively) were calculated for each estimated raw score, and these terms were entered into Equation 1 to determine intercepts and regression weights for the actual T-score transformations. After these weights were obtained, every possible raw score for SzP was entered into the resulting regression equation, and a uniform T score for each raw score was computed. Following the precedent of Tellegen and Ben- Porath, any T score less than 30 obtained by this method was scored as 30.

4 1034 Journal of Clinical Psychology, September 2003 Figure 1. sample. Distribution of Schizophrenia Proneness (SzP) raw scores for females in the MMPI-2 normative Results The mean SzP raw score for females was 8.6 (SD 2.9) and for males was 8.0 (SD 2.9). The observed mean raw score difference is statistically significant, t(2598) 4.50, p.001, d.21, but is approximately one-half of one item in practical terms. Figures 1 and 2 display the raw score distributions for females and males, respectively. Table 2 displays the estimated raw scores for critical percentile rankings (see Tellegen & Ben-Porath, 1992) in the normative group, by gender. Table 3 displays uniform T scores for each raw score, by gender. Effectiveness Evaluations The purpose of SzP is to identify personality characteristics that are associated with an increased likelihood for developing SRIs. Thus, we employed a criterion group consisting of individuals whose MMPI administrations predate the onset of the disorders. A scale that is purported to measure liability to a trait, however, should also be able to identify individuals who already possess that trait; to guard against the possibility of SzP being ineffective as an indicator of concurrent schizophrenia, we also employed a postmorbid construct validation group a group of individuals who had already developed the disorder. Following the advice of Butcher, Graham, and Ben-Porath (1995), we examined not only the scale s singular validity as an indicator of personality processes associated with the development of schizophrenia but also its incremental validity over Scale 8 (Sc; K-corrected) as an indicator of liability to schizophrenia.

5 The Schizophrenia Proneness Scale 1035 Figure 2. sample. Distribution of Schizophrenia Proneness (SzP) raw scores for males in the MMPI-2 normative Method Participants. Three separate samples were employed to form two distinct study groups for the following analyses. Our criterion diagnosis of SRI consists of several disorders that research has demonstrated to be both conceptually and genetically related to schizophrenia and includes schizophrenia, schizoaffective disorder, and Cluster A personality disorders (Erlenmeyer-Kimling et al., 1997). A premorbid group, consisting of individuals from the New York High-Risk Project (NYHRP; Erlenmeyer-Kimling & Cornblatt, 1988; Erlenmeyer-Kimling et al., 1984, 1997), was used to assess SzP s ability to identify individuals who would later (mean time to diagnosis 14 years) experience the onset of SRI. A postmorbid group, consisting of individuals from the Torrey-Gottesman National Institute of Mental Health (NIMH; Torrey, Bowler, Taylor, & Gottesman, 1994) study of identical twins discordant for schizophrenia, as well as members of Gottesman and Shields s (1972) Maudsley Twin Study, was created to test the construct validity of the scale. Each of these samples is described below. A common problem when examining MMPI profiles is separating those profiles that reflect true psychiatric deviance from those that reflect psychometric noise. The use of a strict set of invalidation or exclusion criteria increases the risk of labeling as invalid those profiles that are, in fact, indicative of psychopathology; use of lenient criteria may allow enough noise into the analyses to mask genuine signals. In an effort to maintain consistency with prior, similar studies (cf. Bolinskey et al., 2001; Moldin et al., 1990), we adopted a moderate set of exclusion criteria to examine the profile validity of the MMPIs in the current study: (a) omission of 40 or more items; (b) Infrequency (F) raw score of 26 or greater; (c) Lie (L) raw score of 10 or greater; and (d) any evidence of mental

6 1036 Journal of Clinical Psychology, September 2003 Table 2 Schizophrenia Proneness (SzP) Raw Scores by Gender for Absolute Percentiles, With Corresponding Uniform T Score Raw Score Percentile T Score Male Female Note. Raw scores are estimated from group midpoints. retardation or the inability to read at the eighth-grade level. 1 Profiles exceeding these criteria were excluded from the sample. Each of the participants completed the original form of the MMPI (Hathaway & McKinley, 1983); however, in recognition of the fact that the MMPI-2 (Butcher et al., 2001) has all but replaced the original form in research and clinical use, we transformed all basic clinical scales to MMPI-2-equivalent T scores by dropping deleted items from MMPI raw scores and calculating MMPI-2 T scores from the tables in the manual. The New York High-Risk Project. The participant pool for the current study has been previously described by Bolinskey et al. (2001); briefly, the sample includes 283 offspring (141 male, 142 female) in the NYHRP and 118 of their siblings (62 male, 56 female) for whom archival MMPIs and current diagnostic information were available. We chose to reanalyze these data so that comparisons could be made between the results obtained with the original (MMPI) version of SzP using a relatively narrow definition of schizophrenia and the results of the current study. 1 Our profile validity estimations may have been greatly enhanced had we been able to include additional MMPI-2 validity scales, such as Fb, the True Response Inconsistency Scale (TRIN), or the Variable Response Inconsistency Scale (VRIN). We were unable to include these scales, however, because each of our participants had completed the original form of the MMPI; this form contains too few items from these scales to score them effectively.

7 The Schizophrenia Proneness Scale 1037 Table 3 Uniform T-Score Conversions for Schizophrenia Proneness (SzP) by Gender T Score Raw Score Male Female After dropping those participants (N 10) who failed to meet the profile validity criteria above, the total number of participants available for the current analyses was 391. Twenty individuals (12 male, 8 female) currently meet our criteria for a SRI diagnosis, whereas 371 individuals (183 male, 188 female) do not. Individuals with a diagnosis of SRI (M 30.1, SD 2.9) were significantly older at time of testing than those individuals not meeting diagnostic criteria (M 27.2, SD 5.0), F(1,390) 6.377, p.012, d.71. All diagnoses were made blind to the MMPI. The Torrey Gottesman/NIMH Study of MZ Twins. Sampling procedures for the NIMH study of identical twins discordant for schizophrenia have been described elsewhere (Torrey et al., 1994). The current study includes those individuals for whom MMPI data meeting the above-outlined validity criteria were available. Although these individuals were recruited as part of a twin study, we treat each as an individual, rather than as a single member of a twin pair. Diagnoses are based upon original diagnoses but also incorporate any available follow-up diagnostic information.

8 1038 Journal of Clinical Psychology, September 2003 Eighty-three individuals (53 male, 30 female) were included in the present study. Mean age at time of MMPI testing for the male participants is 29.2 years (SD 7.2), and mean age for females is 32.2 (SD 8.6); the observed difference in age between the gender groups was not significant at the level of.05 (d.38). Although a similar age difference was found to be statistically significant within the NYHRP, the current age difference was not found to reach levels of significance; this is due to having a larger sample size in the NYHRP as well as less variance within age, the latter phenomenon being a direct result of the selection process. The lower values of Cohen s d reflect the effects of increased age variance in the NIMH sample. Thirty-nine individuals (30 male, 9 female) currently meet criteria for a diagnosis of SRI, whereas 44 individuals (23 male, 21 female) do not. Mean age at time of MMPI testing for affected individuals was 29.4 (SD 7.4), and mean age for nonaffected individuals was 31.1 (SD 8.2); the observed between-groups difference is not significant at the level of.05 (d.22). Age differences by gender for nonaffected individuals were also nonsignificant; however, for affected individuals, males (M 25.7, SD 6.5) were found to be significantly younger than females (M 35.0, SD 8.0), F(1,32) 8.034, p.007, d All diagnoses were made blind to the MMPI, except for two co-twins (Torrey et al., 1994, p. 219). The Gottesman Shields Maudsley Twin Study. The current sample included 65 of Gottesman and Shields s (1972) twins 32 A-twins and 33 B-twins and 22 family members 4 same-gender siblings of probands, 8 fathers, 9 mothers, and 1 wife for whom MMPI profiles meeting the validity criteria outlined above were available. Psychiatric diagnoses used in the current study are based on those of Farmer, McGuffin, and Gottesman (1987), as well as those provided by Alastair Cardno (2000), and are based on research diagnostic criteria (RDC; Spitzer, Endicott, & Robins, 1975) and Diagnostic and Statistical Manual of Mental Disorders (3rd ed.; American Psychiatric Association, 1980) criteria; all are made blind to the MMPI. Mean age at time of MMPI testing for the male participants is 37.6 years (SD 12.9), and mean age for females is 43.2 (SD 14.3); the observed difference in age between the gender groups was not significant at the level of.05 (d.41). As was noted in our description of the NIMH sample, a smaller age difference was found to be statistically significant within the NYHRP because of a larger sample size and less variance within age. By our definition of SRI, 36 individuals (19 male, 17 female) are affected, whereas 51 individuals (25 male, 26 female) are not. Mean age at time of MMPI testing for affected individuals was 36.4 (SD 12.1), and mean age for nonaffected individuals was 43.2 (SD 14.4). Affected individuals were significantly younger at time of testing than nonaffected individuals, F(1,86) 5.39, p.023, d.51; however, this difference was expected because of the large number of parents within the nonaffected group. Age differences by gender were nonsignificant, as was the interaction between gender and diagnostic class. Design and Procedures. Participants from the NYHRP served as a study group to examine the effectiveness of SzP as a predictor of liability to developing SRI; the combined NIMH/Maudsley groups served as a construct validation sample (Cronbach & Meehl, 1955). Effectiveness was assessed for each sample in three ways: (a) by performing univariate analyses of group mean scores; (b) by performing logistic regression analyses to determine whether a cutting T score of 65 is useful in identifying diagnostic group; and (c) by examining the incremental validity of SzP over Scale 8 (Sc) as a predictor of increased liability to developing SRI. We would like to note that whereas Ben-Porath,

9 The Schizophrenia Proneness Scale 1039 Table 4 Internal Consistency Estimates for Schizophrenia Proneness (SzP) by Sample Group N Std. MMPI-2 Restandardization Sample 2, NYHRP and NIMH/Maudsley Combined With SRI Without SRI Note. Cronbach s coefficient alpha; Std. standardized alpha. MMPI-2 Minnesota Multiphasic Personality Inventory 2; NYHRP New York High-Risk Project; NIMH National Institute of Mental Health; SRI schizophrenia-related illness. Butcher, and Graham (1991) incorporated hierarchical linear regression models (using a dummy variable for diagnostic class) for assessments of incremental validity, we chose to incorporate hierarchical logistic regression models for the present study, which may provide more stable results when used with a nominal criterion variable. Results Univariate Comparisons. Internal consistency estimates for SzP are shown in Table 4. As would be expected, the observed internal consistency values for SzP appear to increase as a function of the density of SRI (or the liability thereto) within the samples evaluated. Analysis of variance (ANOVA) was performed to examine mean score differences by diagnosis (SRI or no SRI), sample (NYHRP vs. NIMH/Maudsley), and their interaction. Results revealed that individuals who would later experience the onset of SRI or had previously suffered the onset of one of the disorders (M 66.6, SD 17.6) had significantly higher mean SzP T scores than the comparison groups (M 48.1, SD 10.0), F(1,561) 199.7, p.001, d There was no significant main effect for sample membership, or for the interaction term (see Figure 3). Diagnostic Classification. Sensitivity, specificity, positive predictive power (PPP), negative predictive power (NPP), and overall classification rates for both samples are displayed in Table 5. Logistic regression analysis within the premorbid sample revealed that SzP scores are relatively effective predictors of correct diagnostic classification, 2 (1, N 391) 33.4, p Likewise, logistic regression analysis within the postmorbid group revealed SzP s effectiveness as a diagnostic indicator with regards to SRI, 2 (1, N 170) 28.3, p Incremental Validity. We next examined the incremental validity of SzP over Sc as a predictor/indicator of liability to SRI. Ben-Porath and colleagues (Ben-Porath et al., 1991) have suggested that any new MMPI-2 scale should evidence utility beyond that which is available through the use of currently available scales. Briefly, an incremental validity investigation consists of a modified regression analysis in which variables, or groups of variables, are entered in blocks, or groups, whose orders of entry are determined a priori by the investigator; within each block, entry order can be either simultaneous or stepwise. The purpose of an incremental validity investigation is to examine whether a scale accounts for additional variance once a preexisting scale, or group of scales, has been allowed to account for as much variance as possible. Because of the stepwise nature of this type of analysis, shared variance is always attributed to the vari-

10 1040 Journal of Clinical Psychology, September 2003 Figure 3. Mean Schizophrenia Proneness (SzP) T score by diagnosis and sample group. SRI schizophreniarelated illness; NYHRP New York High-Risk Project; NIMH National Institute of Mental Health. able that enters the equation first; thus, many investigators will perform an additional series of analyses with order entry reversed. As noted above, we chose to incorporate logistic regression, rather than linear regression, in our hierarchical models, because of the dichotomous nature of our dependent variable. Analyses were performed separately for our pre- and postmorbid groups. In the initial series of analyses, Sc was entered in Block 1 and SzP was entered in Block 2; a stepwise method was incorporated to prohibit a variable from entering the equation if it did not contribute significantly to the prediction, and change was assessed using the likelihood ratio test (Klein & Moeschberger, 1997). Table 5 Effectiveness Indicators for Schizophrenia Proneness (SzP) in Different Samples by Diagnosis Actual Sample Predicted SRI Comparison Accuracy PPP NPP Sensitivity Specificity NYHRP SRI Comparison NIMH/ Maudsley SRI Comparison Note. SRI schizophrenia-related illness; PPP positive predictive power; NPP negative predictive power; NYHRP New York High-Risk Project; NIMH National Institute of Mental Health.

11 The Schizophrenia Proneness Scale 1041 Table 6 Hierarchical Logistic Regression Analyses Predicting Schizophrenia-Related Illness (SRI) Versus Absence of SRI Sample Entry Block Scale Entered Model 2 df 2 Log Likelihood p (change) Nagelkerke R 2 NYHRP Initial 1* Sc * SzP Reverse 1* SzP Sc NIMH/ Maudsley Initial 1* Sc * SzP Reverse 1* SzP * Sc Note. p (change) probability of change in 2 log likelihood; NYHRP New York High-Risk Project; NIMH National Institute of Mental Health; SC Scale 8; SzP Schizophrenia Proneness. *p.001 for full model. Results from the initial entry order indicate that SzP makes a significant incremental contribution to the prediction of SRI, accounting for an additional 5% of the variance in the premorbid group and 4% of the variance in the postmorbid group (see Table 6; initial entry). Following the conventions of Ben-Porath et al. (1991), we also reversed the order entry of the variables (i.e., SzP was entered in Block 1, followed by Sc in Block 2) and performed an additional series of analyses. As seen in Table 6 (reverse entry), when SzP is entered into the equation first, Sc does not make a significant contribution to the prediction of SRI in the premorbid group, although it does contribute significantly to the prediction of the disorder in the postmorbid group. In the premorbid group, SzP alone accounts for 24% of the observed variance. General Discussion Results of ANOVA revealed that those participants in the NYHRP sample who later developed SRIs scored significantly higher on SzP than those participants who did not. Participants in the combined NIMH/Maudsley group who had previously been diagnosed with SRI also scored higher on SzP than their nonaffected counterparts. There was no main effect for sample membership. This suggests that SzP measures personality processes that are common to SRI both pre- and postmorbidly. Examination of the psychometric properties of SzP revealed that the scale is a moderately effective indicator of liability to SRI. Participants within the NYHRP who later developed SRI and those within the NIMH/Maudsley sample who had previously developed SRI scored significantly higher on the scale than those participants who did not manifest the onset of the disorders. Furthermore, those individuals with high scores on the scale had a significantly higher likelihood of a diagnosis of SRI than those with low scores on the scale. Results of the incremental validity analyses suggested that SzP makes a small but significant contribution over Sc to the prediction of SRI in both pre- and postmorbid samples. Moreover, SzP appears to be more effective than Sc as a premorbid predictor, although Sc appears to be more effective as a postmorbid indicator. This latter finding

12 1042 Journal of Clinical Psychology, September 2003 suggests that whereas Sc measures the results of having developed SRI, SzP may measure the process of developing the disorder. Further research is necessary, however, to explore this issue (Gottesman & Gould, 2003). For now, high scores on SzP should be considered from a probabilistic, rather than deterministic standpoint; although SzP appears to be a moderately effective indicator of liability to developing SRI, high scores on the scale should not be taken to warrant firm conclusions of future liability to SRI breakdown. Additional research is necessary to further establish the predictive validity of high SzP scores. Furthermore, we urge that use of SzP be restricted to research purposes until such time as behavioral correlates are available. Caution is key in the interpretation of any single indicator of a disorder (cf. Gottesman & Erlenmeyer-Kimling, 2001), and it is especially urged with SzP, asa substantial number of high scorers have never had any type of psychiatric disorder, although they appear to share certain personality characteristics, as measured by SzP, in common with individuals who later decompensate into an SRI. These characteristics may reflect an incomplete expression of a genotype, although given the lack of specific genetic markers for schizophrenia, any specific genetic correlates remain hypothetical. At the present time, none of the hypothesized indicators of premorbid SRI have proven to be effective singular predictors of the disorder, although several indicators have shown modest effect sizes (Heinrichs, 2001). Unfortunately, it remains true that the single best predictor of developing SRI is having a monozygotic twin with the disorder (Meehl, 1962); recent research has been somewhat successful in using multiple predictors as indicators of liability to the disorders (Bolinskey et al., 2001; Erlenmeyer-Kimling et al., 2000). Meehl (1990) demonstrated that multiple indicators of small or moderate effect can be bootstrapped into a single indicator of higher effect, and similar findings are apparent in the field of human genetics (cf. Gottesman, 1997); it appears that SzP meets the criteria for inclusion in such an index of multiple indicators for SRI. In this tradition, we offer SzP as a candidate for further research. Appendix Items of the Schizophrenia Proneness (SzP) Scale True items: False items: Note. Item numbers correspond to the item location on the MMPI-2. References American Psychiatric Association. (1980). Diagnostic and statistical manual of mental disorders (3rd ed.). Washington, DC: Author. Ben-Porath, Y.S., Butcher, J.N., & Graham, J.R. (1991). Contribution of the MMPI-2 content scales to the differential diagnosis of schizophrenia and major depression. Psychological Assessment, 3, Bolinskey, P.K., Gottesman, I.I., Nichols, D.S., Shapiro, B.M., Roberts, S.A., Adamo, U.H., & Erlenmeyer-Kimling, L. (2001). A new MMPI-derived indicator of liability to developing schizophrenia: Evidence from the New York High-Risk Project. Assessment, 8, Butcher, J.N., Graham, J.R., & Ben-Porath, Y.S. (1995). Methodological problems and issues in MMPI, MMPI-2, and MMPI-A research. Psychological Assessment, 7,

13 The Schizophrenia Proneness Scale 1043 Butcher, J.N., Graham, J.R., Ben-Porath, Y.S., Tellegen, A., Dahlstrom, W.G., & Kaemmer, B. (2001). MMPI-2: Manual for administration and scoring (Rev. ed.). Minneapolis: University of Minnesota Press. Cardno, A.G. (2000). [OPCRIT diagnoses for Maudsley Twin Study of Schizophrenia]. Unpublished raw data. Carter, J.W., Parnas, J., Cannon, T.D., Schulsinger, F., & Mednick, S.A. (1999). MMPI variables predictive of schizophrenia in the Copenhagen High Risk Project: A 25-year follow-up. Acta Psychiatrica Scandinavica, 99, Cronbach, L.J., & Meehl, P.E. (1955). Construct validity in psychological tests. Psychological Bulletin, 52, Erlenmeyer-Kimling, L., Adamo, U.H., Rock, D., Roberts, S.A., Bassett, A.S., Squires-Wheeler, E., Cornblatt, B.A., Endicott, J., Pape, S., & Gottesman, I.I. (1997). The New York High-Risk Project: Prevalence and comorbidity of Axis I disorders in offspring of schizophrenic parents at 25-year follow-up. Archives of General Psychiatry, 54, Erlenmeyer-Kimling, L., & Cornblatt, B. (1988). The New York High-Risk Project: A follow-up report. Schizophrenia Bulletin, 13, Erlenmeyer-Kimling, L., Marcuse, Y., Cornblatt, B., Friedman, D., Rainer, J.D., & Rutschmann, J. (1984). The New York High-Risk Project. In N. Watt, E.J. Anthony, L. Wynne, & J. Rolfe (Eds.), Children at risk for schizophrenia: A longitudinal perspective (pp ). New York: Cambridge University Press. Erlenmeyer-Kimling, L., Rock, D., Roberts, S.A., Janal, M., Kestenbaum, C., Cornblatt, B., Adamo, U.H., & Gottesman, I.I. (2000). Attention, memory, and motor skills as childhood predictors of schizophrenia-related psychoses: The New York High-Risk Project. American Journal of Psychiatry, 157, Farmer, A.E., McGuffin, P., & Gottesman, I.I. (1987). Twin concordance for DSM III schizophrenia: Scrutinizing the validity of the definition. Archives of General Psychiatry, 44, Gottesman, I.I. (1997). Twins: En route to QTLs for cognition. Science, 276, Gottesman, I.I., & Erlenmeyer-Kimling, L. (2001). Family and twin strategies as a head start in defining prodromes and endophenotypes for hypothetical early-interventions in schizophrenia. Schizophrenia Research, 51, Gottesman, I.I., & Gould, T.G. (2003). The endophenotype concept in psychiatry: Etymology and strategic intentions. American Journal of Psychiatry, 160, Gottesman, I.I., & Shields, J. (1972). Schizophrenia and genetics: A twin study vantage point. New York: Academic Press. Greene, R.L. (2000). The MMPI-2: An interpretive manual (2nd ed.). Needham Heights, MA: Allyn & Bacon. Hathaway, S.R., & McKinley, J.C. (1983). Manual for administration and scoring of the MMPI. Minneapolis, MN: National Computer Systems. Heinrichs, R.W. (2001). In search of madness: Schizophrenia and neuroscience. New York: Oxford University Press. Klein, J.P., & Moeschberger, M.L. (1997). Survival analysis: Techniques for censored and truncated data. New York: Springer. Meehl, P.E. (1962). Schizotaxia, schizotypy, and schizophrenia. American Psychologist, 17, Meehl, P.E. (1990). Toward an integrated theory of schizotaxia, schizotypy, and schizophrenia. Journal of Personality Disorders, 4, Moldin, S.O., Gottesman, I.I., Erlenmeyer-Kimling, L., & Cornblatt, B.A. (1990). Psychometric deviance in offspring at risk for schizophrenia: I. Initial delineation of a distinct subgroup. Psychiatry Research, 32, Rosen, A. (1962). Development of MMPI scales based on a reference group of psychiatric patients. Psychological Monographs, 76(Whole No. 527), 1 25.

14 1044 Journal of Clinical Psychology, September 2003 Spitzer, R.L., Endicott, J., & Robins, E. (1975). Research diagnostic criteria (RDC) for a selected group of functional disorders (2nd ed.). New York: New York State Psychiatric Institute, Biometrics Research. Tellegen, A., & Ben-Porath, Y.S. (1992). The new uniform T scores for MMPI-2: Rationale, derivation, and appraisal. Psychological Assessment 4, Torrey, E.F., Bowler, A.E., Taylor, E.H., & Gottesman, I.I. (1994). Schizophrenia and manicdepressive disorder: The biological roots of mental illness as revealed by the landmark study of twins. New York: Basic Books. Wiggins, J.S. (1966). Substantive dimensions of self-report in the MMPI item pool. Psychological Monographs, 80(Whole No. 630), 1 42.