Minnesota Multiphasic Personality Inventory profile characteristics of schizotypal personality disorder

Authors


address: Mié Matsui, Department of Psychology, School of Medicine, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan. Email: mmatsui@ms.toyama-mpu.ac.jp

Abstract

Abstract The goal of the present study was to determine whether precursors for psychopathology can be found in personality dimensions of the general population. Two hundred and 62 university students were compared with 41 schizophrenic patients and 18 patients with schizotypal personality disorder (SPD) on the Minnesota Multiphasic Personality Inventory (MMPI). Schizotypal personality disorder patients showed significantly elevated Pt and Si scales compared with the schizophrenic patients. Schizophrenia and SPD groups generally produced two-point codetypes of 6–8/8–6, 2–6/6–2, 7–8/8–7, and 7–8/8–7, 2–7/7–2, 6–8/8–6. A total of 77.5% of students had no codetype with a T-value of ≥ 70, although the frequency of codetypes of spike 5, spike 0 and 2–7/7–2 was relatively high in the student group compared with the general population. Discriminant function analysis of the MMPI profiles revealed significant variance among the three groups. The overall rate of correct classification of the subjects into schizophrenia, SPD or university students was 90.3%. The first coefficient, mainly defined by a negative weight on the Sc scale, best distinguished the patients with either schizophrenia or SPD from the students. The second coefficient, defined by negative weights on the Sc and Si scales, and positive weights on the F and Ma scales identified patients with schizophrenia and SPD patients. The Harris-Lingoes subscales, which are supposed to provide the profile patterns characteristic of schizotypy, well discriminated the three groups. These results suggest the usefulness of the MMPI subscales for the detection of subjects with the SPD trait.

INTRODUCTION

The Minnesota Multiphasic Personality Inventory (MMPI) is one of the widely used objective tests of personality and has the ability to detect both schizophrenia and schizophrenia-related conditions to some degree. It also provides transmissible indicators for the liability to develop schizophrenia.1,2 Several previous studies have attempted to determine in healthy people whether precursors for psychopathology can be found in personality dimensions, which are measured by the MMPI. Thus, Claridge and Beech described the dimensional personality-based continuity models of schizotypy and schizophrenia.3 This model predicts that the trends toward psychopathological personality in healthy people predisposes to psychopathology (i.e. the biological liability for schizophrenia may be expressed as schizotypal personality organization).3 Some studies have attempted to clarify in healthy people the association between personality traits as assessed by the MMPI and biological markers.4–7 Recently, Matsui et al. have provided evidence that in healthy people the high Sc scale of the MMPI was associated with reduced frontal white matter volume as measured by magnetic resonance imaging (MRI).4 These findings suggest that personality dimensions may be linked to some neural substrates.

Other investigators have administered several kinds of psychological tests, in addition to the MMPI, to university students in order to identify individuals who have schizotypal personality, and compared the MMPI profiles between subjects who were considered to have schizotypal personality and those who were not.8–10 Thus, Haier et al. compared results from the MMPI and those from the Research Diagnostic Criteria (RDC) in college students, and found a certain degree of correlation between specific MMPI codetypes and the RDC evaluations.8 Similarly, Moldin et al. identified the schizophrenia-related codetypes of the MMPI.11 Lenzenweger9 used the Perceptual Aberration Scale (PAS)12 as a measure of schizotypal personality, and found that the PAS-identified schizotypic students showed schizophrenia-related MMPI high-point codes more frequently than the controls. On the other hand, Merritt et al.10 found no evidence for correlations between the diagnosis of schizotypy based on the Social Anhedonia Scale (SAS)13 and the MMPI profiles.

The primary purpose of the present study was to compare the MMPI profiles, including the schizophrenia-related high-point codetypes11 in addition to the individual subscales, among patients with either schizophrenia or schizotypal personality disorder (SPD) and university students. In addition, as the codetypes of MMPI typically have been determined according to the high-point pairs (i.e. the two highest scales with T scores of more than 70),14 we examined all two-point codetypes and compared them between patients with schizophrenia and those with SPD. The second purpose was to determine the ability of the MMPI to distinguish among subjects with schizophrenia or SPD, and normal students, using multiple discriminant function analyses. In view of the continuity models of healthy people and patients with schizophrenia-spectrum disorders, it is hypothesized that a certain degree of overlap between university students and patients with schizophrenia or SPD exists in terms of the MMPI profiles. Therefore, we sought to identify a measure of the liability to schizotypy by analyzing the MMPI profiles. Our a priori hypothesis was that subjects with SPD are associated with more distress, irrational struggle, social withdrawal and so on, which are represented by the corresponding MMPI subscales and profiles, compared with patients with schizophrenia or normal students.

METHODS

Subjects

The sample included 326 participants (59 patients and 267 students). A total of 267 freshmen (115 males and 152 females) who entered Toyama Medical and Pharmaceutical University, Toyama, Japan, in 1998 participated in the study. The mean age of these subjects at the time of testing was 19.2 (SD 2.1) years.

The clinical group consists of 41 patients with schizophrenia (23 males and 18 females) and 18 patients with schizotypal disorder (17 males and one female) who meet the ICD-10 Diagnostic Criteria for Research.15 Schizotypal disorder is characterized by eccentric behavior and anomalies of thinking and affect which resemble those seen in schizophrenia, although no definite and characteristic schizophrenic anomalies have occurred. The clinical picture of schizotypal disorder is similar to the prodromal state of schizophrenia. The phenomenological differences between schizotypal disorder and schizophrenia are the absence of overt symptoms and the presence of sustained psychotic symptoms. Eighteen patients with schizotypal disorder have never met criteria for schizophrenia itself. The mean age of schizophrenia and SPD subjects was 29.2 (SD 7.0) and 24.0 (SD 8.0) years, respectively. All patients were under 45 years of age. The mean duration of illness for the schizophrenia and SPD subjects was 4.6 (SD 5.1, range 0.08–21) and 2.2 (SD 2.9, range 0.02–11) years, respectively. The mean daily haloperidol-equivalent neuroleptic doses for schizophrenia and SPD subjects were 8.6 (SD 8.9, range 0.6–37.8) and 4.4 (SD 8.2, range 0–32.9) mg, respectively. Diagnoses were made by experienced psychiatrists using medical histories. All patients were physically healthy at the time of the study, and no patient had a history of head trauma, serious medical or surgical illness, or substance abuse.

Personality assessment

All subjects gave informed consent before entering the study. The new Japanese version of Minnesota Multiphasic Personality Inventory (MMPI) was administered to students as a routine mental health checkup during the orientation following entrance into the university. All patients were administered the full version of the MMPI by well-trained clinical psychologists in a quiet, comfortable, conventionally lit testing room. The MMPI is a widely used instrument for personality assessment with established psychometric properties. The new Japanese version of the MMPI was recently revised following comprehensive re-standardization in 1993.16 To date, there have been several Japanese versions of the MMPI which have been used since the 1950s. However, they were viewed as decreasingly applicable in contemporary society, as the original Japanese MMPI items and norms were translated and developed about 40–50 years ago. The last Japanese version had some problems: one problem is that of mistranslation; second, there was sample bias of population for normalization (i.e. 80% of subjects was less than 30 years old); third, basic materials of normalization such as percentage of endorsement and distribution of two-point codes have not been published. The new Japanese version was based on the MMPI, but not MMPI-2, as there has been vast information on the MMPI. The new version was developed based on considerations of nine previous Japanese versions. Sampling for normalization was based on a national census. Thus, the validity and reliability of the new version of MMPI have been confirmed17 and it is at present in common use in Japan.

Initially, we analyzed the 13 basic scores consisting of three validity and 10 clinical scores. The three validity scales (L, lie; F, infrequency; K, defensiveness) provide information about the subject's approach to the test including accuracy of the self-appraisal by the subject, which can also reveal psychopathology to some degree.14 The 10 clinical scales provide levels of symptomatology in specific pathological domains and information on personality including hypochondriasis (Hs; code 1), depression (D; code 2), hysteria (Hy; code 3), psychopathic deviate (Pd; code 4), paranoia (Pa; code 6), psychasthenia (Pt; code 7), schizophrenia (Sc; code 8), mania (Ma; code 9), masculinity-femininity (Mf; code 5), and social introversion (Si; code 0). Second, the Harris-Lingoes and the Serkownek subscales were examined. The Harris-Lingoes subscales for depression, paranoia and schizophrenia, and the Serkownek subscales for social introversion provide more detailed information on domains associated with schizotypy, and allow more subtle analysis of an individual's clinical scale elevations.14 The depression subscales include subjective depression (D1), psychomotor retardation (D2), physical malfunctioning (D3), mental dullness (D4), and brooding (D5). The paranoia subscales include persecutory ideas (Pa1), poignancy (Pa2), and naivete (Pa3). The schizophrenia subscales include social alienation (Sc1), emotional alienation (Sc2), lack of ego mastery, cognitive (Sc3), lack of ego mastery, conative (Sc4), lack of ego mastery, defective inhibition (Sc5), and bizarre sensory experiences (Sc6). The social introversion subscales include inferiority-personal discomfort (Si1), discomfort with others (Si2), staid-personal rigidity (Si3), hypersensitivity (Si4), distrust (Si5), and physical-somatic concerns (Si6).

A T score is a standard score, whose distribution has a mean of 50 and a standard deviation of 10. Raw scores on the MMPI are converted to T scores in order to permit interscale comparisons. K-corrected MMPI T scores of basic scores were used in the analyses. The frequency of individual MMPI scale elevations, as well as the ‘TOP3’, ‘Highest’, and ‘Any’, as employed by Holdnack et al.,18 was obtained per group (schizophrenia, schizotypal disorder and students). The scales were considered elevated when T ≥ 70. The TOP3 means that the scale is one of the three highest elevations. The Highest means that the scale was the highest elevation in the profile, and ‘Any’ shows that the scale was elevated above 70 T.

Moreover, the classification strategy employed by Moldin et al.11 was used to classify groups according to elevated profiles specific to schizophrenia spectrum disorders. By this classification, the following codetypes are regarded to be associated with the spectrum disorders: 2-7-8, 2-8, 4-6, 4-2-8, 8-6, 8-9, 9-6, 8-3, and 8-1-3.

Statistical analysis

Multivariate analysis of variance (MANOVA) was used for overall analysis of the MMPI subscales following the previous MMPI studies.18,19 Fisher's exact probability tests were employed to examine the differences in the frequency of scale elevations and the Moldin's codes between schizophrenia and SPD. An alpha level of 0.05 was used for these statistical tests.

Discriminant function analysis was performed using the MMPI basic scores and other scores by the Harris-Lingoes Subscales and the Serkownek Subscales in order to discriminate among patients with schizophrenia or schizotypal disorder, and university students.

RESULTS

Group differences

Profile analysis

Basic scores: Five of 267 students (1.9%) were excluded from the analysis because the T scores of the Cannot Say (?) scale of these students were higher than 70. Therefore, data from the remaining 262 students were examined. Means and standard deviations derived from K-corrected T scores of the MMPI 3 validity scores and 10 clinical scales are listed in Table 1.

Table 1.  Mean and standard deviation of the Minnesota Multiphasic Personality Inventory validity and clinical scales
 Schizophrenia
(n = 41)
Schizotypal
disorder (n = 18)
Students
(n = 262)
manova 
 MeanSDMeanSDMeanSDFPSheefe's test
  • L, lie; F, frequency; K, defensiveness; Hs, hypochondriasis; D, depression; Hy, hysteria; Pd, psychopathic deviate; Mf, masculinity-femininity; Pa, paranoia; Pt, psychasthenia; Sc, schizophrenia; Ma, mania; Si, social introversion.

  • A, schizophrenia vs SPD; B, schizophrenia vs students; C, SPD vs students.

  • *

     P < 0.05;

  • **

     P < 0.01;

  • ***

     P < 0.001.

L53.59 (9.72)49.89 (8.00)48.29 (8.73) 6.480.0017B**
F66.27(16.00)66.83(18.78)49.49(10.85) 46.84< 0.0001B***C***
K48.83(10.60)46.39 (9.65)50.01 (9.17) 1.430.2403
Hs62.66(13.12)64.56(14.67)51.95 (9.44) 29.06< 0.0001B***C***
D69.12(14.07)75.33(12.31)52.08(11.89) 59.56< 0.0001B***C***
Hy65.41(13.61)64.39(11.64)50.93 (9.12) 49.01< 0.0001B***C***
Pd63.63(12.84)63.11 (8.68)49.64 (9.72) 45.02< 0.0001B***C***
Mf53.95(11.62)54.67(11.78)51.46 (9.38) 1.870.1565
Pa70.90(16.33)71.11(16.35)48.38 (9.07)106.38< 0.0001B***C***
Pt70.32(14.26)78.50(15.63)49.66(10.46)103.75< 0.0001A*B***C***
Sc74.05(17.13)80.56(16.03)47.17 (9.16)170.04< 0.0001B***C***
Ma57.29(11.34)51.94(9.02)47.60 (9.23) 28.92< 0.0001B***C*
Si55.37(10.45)65.22(10.30)51.65(11.73) 12.8< 0.0001A*C***

The MANOVAs were employed to test the hypotheses that the three groups (schizophrenia, SPD, and students group) would respond differently to the MMPI. The validity scales and clinical scales were analyzed separately, as was each group of the Harris-Lingoes and Serkownek subscales (e.g. depression, paranoia, schizophrenia, and social introversion).

A MANOVA of the validity scales lie (L), infrequency (F), and defensiveness (K), found a main effect for the group (F[6, 632] = 18.3, P < 0.001, with L and F significant at the univariate, P < 0.005 and P < 0.001, respectively). Means (± SD) for the validity scales are shown in Table 1. There was no significant difference between schizophrenia and SPD in this respect.

Table 1 also details the means and standard deviations for each clinical scale. A significant main effect of the group (F[20, 618] = 17.1, P < 0.001) was observed for all clinical scales significant at the univariate level except Mf. The SPD patients showed significantly elevated Pt and Si scales compared with schizophrenia patients (Scheffe's post-hoc test, P < 0.05). Schizophrenic patients had significantly higher all clinical scales except Si compared to students. The SPD patients also scored significantly higher than students on every clinical scale.

The Harris-Lingoes and Serkownek subscales: The means and standard deviations for each Harris-Lingoes and Serkownek subscale are shown in Table 2.

Table 2.  Mean and standard deviation on the Minnesota Multiphasic Personality Inventory Harris-Lingoes subscales
 Schizophrenia
(n = 41)
Schizotypal
disorder (n = 18)
Students
(n = 262)
manova 
 MeanSDMeanSDMeanSDFPSheefe's test
  • D1, subjective depression; D2, psychomotor retardation; D3, physical malfunctioning; D4, mental dullness; D5, brooding; Pa1, Persecutory ideas; Pa2, Poignancy; Pa3, Naivete; Sc1, social alienation; Sc2, emotional alienation; Sc3, lack of ego mastery, cognitive; Sc4, lack of ego mastery, conative; Sc5, lack of ego mastery, defective inhibition; Sc6, bizarre sensory experience; Si1, inferiority-personal discomfort; Si2, discomfort with others; Si3, staid-personal rigidity; Si4, hypersensitivity; Si5, distrust; Si6, physical-somatic concerns.

  • A, schizophrenia vs SPD; B, schizophrenia vs students; C, SPD vs students.

  • *

     P < 0.05;

  • **

     P < 0.01;

  • ***

     P < 0.001.

D164.24(13.84)76.33(12.32)51.08(12.16)50.42< 0.0001A**B***C***
D262.17(10.08)65.22(15.45)50.07(12.21)28.02< 0.0001B***C***
D365.59(14.66)67.72(15.49)51.07(11.24)38.78< 0.0001B***C***
D467.17(15.03)75.94(16.68)49.42(11.14)72.54< 0.0001A*B***C***
D561.88(10.73)71.00 (9.47)53.36(11.43)28.41< 0.0001A*B***C***
Pa165.80(17.98)68.22(17.71)49.61 (9.78)50.98< 0.0001B***C***
Pa263.20(13.99)68.28(12.24)53.73(12.23)19.85< 0.0001B***C***
Pa354.29 (9.79)49.61(10.26)50.85 (8.97) 2.810.0618
Sc168.05(14.96)81.89(18.51)52.39(12.43)61.88< 0.0001A**B***C***
Sc256.83(12.37)69.00(15.71)50.56(11.06)25.05< 0.0001A**B**C***
Sc369.44(16.57)76.61(17.29)48.84(11.42)81.43< 0.0001B***C***
Sc463.34(12.19)73.33(15.70)51.64(11.57)41.33< 0.0001A**B***C***
Sc563.83(15.57)63.28(15.48)51.53(11.01)24.82< 0.0001B***C***
Sc671.15(21.47)63.56(20.03)49.90(11.00)50.30< 0.0001B***C***
Si158.34(10.68)65.11(10.23)52.89(11.22)13.35< 0.0001B*C***
Si254.24(10.39)63.00(13.43)48.86(11.41)15.69< 0.0001A*B*C***
Si350.22(10.93)56.67 (7.61)48.66 (9.73) 5.840.0032C**
Si460.54(10.39)59.67(10.61)50.43(10.02)22.9< 0.0001B***C**
Si550.76(12.84)55.00(14.14)48.43(11.44) 3.080.0473
Si661.46(10.52)67.39(11.90)54.00(10.92)19.18< 0.0001B***C***

The main effects for group in the Harris-Lingoes and Serkownek subscales were found for depression (F[10, 628] = 18.4, P < 0.001), paranoia (F[6, 632] = 20.0, P < 0.001), schizophrenia (F[12, 626] = 18.6, P < 0.001), and social introversion (F[12, 626] = 6.09, P < 0.001). Post-hoc tests revealed SPD patients had significantly elevated D1 (subjective depression), D4 (mental dullness), D5 (brooding), Sc1 (social alienation), Sc2 (emotional alienation), Sc4 (lack of ego mastery, conative) and Si2 (discomfort with others) scores compared with schizophrenia patients (D1, Sc1, Sc2, Sc4, Scheffe's test, P < 0.01; D4, D5, Si2, Scheffe's test, P < 0.05).

Scale elevations

The frequency of individual scale elevations, ‘TOP3’, ‘Highest’ and ‘Any’ is shown in Table 3. Schizophrenia patients most often produced elevations on scales Sc (46.3%) and Pa (37.8%). Patients with SPD also produced elevations on scales Sc (75.0%) and Pt (55.6%). In contrast, the frequency of elevations in the university students did not surpass 10% for any scale. Application of the Fisher's exact probability test revealed that schizophrenia and SPD differ in frequency of Hy, Pt, Sc or Si in ‘TOP3’ (< 0.05). Schizophrenia and SPD did not differ in the frequency of any ‘Highest’ scale.

Table 3.  Minnesota Multiphasic Personality Inventory clinical scale elevations
 SchizophreniaSchizotypal disorderStudentsS vs SPD vs StudentsS vs SPD
MMPITOP3HighestAnyTOP3HighestAnyTOP3HighestAnyTOP3HighestAnyTOP3HighestAny
  1. Scales were considered elevated when T ≧ 70. Top 3, the scale was one of the three highest elevations.

  2. Highest, the scale was the highest elevation in the profile; Any, the scale was elevated above or equal to 70.

  3. Values are expressed as % (no. subjects). S vs SPD vs Students; χ 2 tests. SPD vs S; Fisher's exact tests. P < 0.05; ** P < 0.01; *** P < 0.001.

Hs17.07 (7) 2.44 (1)29.27 (12)16.67 (7) 022.22 (9.3)5.15 (13.5)2.67 (7)6.87 (18)** ***   
D28.05 (11.5) 9.76 (4)46.34 (19)36.11 (15.2)19.44 (8.2)72.22 (30.3)6.42 (16.83)3.56 (9.33)6.87 (18)********   
Hy23.17 (9.5) 6.10 (2.5)36.59 (15) 0 027.78 (11.7)2.29 (6)1.15 (3)3.05 (8)*** ****  
Pd19.51 (8) 9.76 (4)34.15 (14) 5.56 (2.3) 5.56 (2.3)27.78 (11.7)2.21 (5.8)1.64 (4.3)3.05 (8)*******   
Mf 7.32 (3) 0 9.76 (4) 0 0 5.56 (2.3)3.44 (9)3.44 (9)3.44 (9)      
Pa37.80 (15.5)14.63 (6)48.78 (20)27.78 (11.7)11.11 (4.7)44.44 (18.7)2.02 (5.3)0.88 (2.3)3.05 (8)*********   
Pt23.17 (9.5) 6.10 (2.5)43.90 (18)55.56 (23.3)25 (10.5)77.78 (32.7)4.81 (12.6)2.52 (6.6)5.73 (15)********** *
Sc46.34 (19)29.27 (12)60.98 (25)75 (31.5)27.78 (11.7)77.78 (32.7)2.02 (5.3)0.88 (2.3)2.67 (7)**********  
Ma 2.44 (1) 012.20 (5) 0 0 01.53 (4)1.53 (4)1.53 (4)  ***   
Si 2.44 (1) 014.63 (6)22.22 (9.3) 044.44 (18.7)4.39 (11.5)2.67 (7)5.75 (15)** **** *

Schizophrenia-related codetypes (Moldin's code) and two-point codetypes

Each participant's MMPI was classified as to the presence or absence of any of the following high-point codes: 2-7-8, 2-8, 4-6, 4-2-8, 8-6, 8-9, 9-6, 8-3, or 8-1-3. Twelve of 41 (29.3%) patients with schizophrenia, eight of 18 (44.4%) patients with SPD and three of 262 (1.1%) students were classified as having one of the Moldin's high-point codes. There was no significant difference between schizophrenia and SPD (Fisher's exact probability test, n.s.). The two-point code, derived from the MMPI clinical scales, is frequently used as an actuarial method for describing personality characteristics. In the present study, each subject was assigned with a two-point code in accordance with the guidelines established by the revision17 based on Hathaway and Meehl,20 such that 85.7% of patients with schizophrenia, 88.9% of patients with SPD and 22.6% of the students were assigned with an appropriate two-point code. The differences in the frequency of the two-point codes among schizophrenia, SPD, and the students were determined. Table 4 provides the frequency with which each MMPI codetype occurred in the group of schizophrenia, SPD and students. Schizophrenic group produced two-point codetypes with 6-8/8-6, 2-6/6-2 and 7-8/8-7 occurring most frequently. Schizotypal personality disorder patients produced two-point codetypes with 7-8/8-7, 2-7/7-2 and 6-8/8-6. A total of 77.5% of students has no two-point codetypes with T-values of ≥ 70, although the frequency of codetypes with spike 5, spike 0 and 2-7/7-2 was relatively high in the students.

Table 4.  Frequency of two-point codetypes
code typeSchizophrenia (n = 41)Schizotypal disorder (n = 18)Students (n = 262)
  1. 1, Hs; 2, D; 3, Hy; 4, Pd; 5, Mf; 6, Pa; 7, Pt; 8, Sc; 9, Ma; 0, Si.

  2. Each subject was assigned with a two-point code in accordance with the guidelines established by the revision based on Hathaway and Meehl.

  3. Scales were considered elevated when T ≧ 70. For example, two kinds of each code got 0.5 when the highest score and the second highest score is a tie or a difference of 1 point.

6 (14.29%)2 (11.11%)203 (77.48%)
1–  4 (1.53%)
2–  4 (1.53%)
3–   
4–1 (2.38%) 2 (0.76%)
5–  9 (3.44%)
6–  1 (0.38%)
7–1 (2.38%) 2 (0.76%)
8–1 (2.38%)1 (5.56%) 
9–  4 (1.53%)
0–  8 (3.05%)
12 · 211.5 (3.57%) 2 (0.76%)
13 · 311 (2.38%) 4.5 (1.72%)
14 · 41   
15 · 51   
16 · 61  0.5 (0.19%)
17 · 71 1 (5.56%)2 (0.76%)
18 · 810.5 (1.19%)  
19 · 91   
10 · 01   
23 · 32   
24 · 42  1 (0.38%)
25 · 52   
26 · 624.5 (13.10%) 1 (0.38%)
27 · 722.5 (5.95%)3.5 (19.44%)6.34 (2.42%)
28 · 821 (2.38%)0.5 (2.78%)0.34 (0.13%)
29 · 92   
20 · 02 1 (5.56%)2 (0.76%)
34 · 431 (2.38%)  
35 · 53   
36 · 63   
37 · 731 (2.38%)  
38 · 832 (4.76%)  
39 · 93   
30 · 03   
45 · 54   
46 · 641 (2.38%) 0.34 (0.13%)
47 · 740.5 (1.19%) 1.34 (0.51%)
48 · 841.5 (3.57%)  
49 · 94   
40 · 04  1 (0.38%)
56 · 65   
57 · 751 (2.38%)  
58 · 85  1 (0.38%)
59 · 95   
50 · 05   
67 · 761 (2.38%) 0.34 (0.13%)
68 · 866.5 (15.48%)3 (16.67%) 
69 · 96   
60 · 06   
78 · 874 (9.52%)5 (27.78%)1.34 (0.51%)
79 · 97   
70 · 07 1 (5.56%) 
89 · 981.5 (3.57%)  
80 · 08   
90 · 09   

Discriminant function analysis

Basic scores

A discriminant function analysis was performed in an attempt to discriminate among schizophrenia, SPD and students group. Minnesota Multiphasic Personality Inventory variables (13 basic scores) were entered stepwise, with a minimum F-value of 1.00 required to enter. Table 5 shows that the disciminant function analysis yielded two significant roots. The first coefficient, mainly defined by a negative weight on Sc, best distinguished the patients with schizophrenia and those with SPD from students. The second coefficient, defined by negative weights on Sc and Si and positive weights on F and Ma, identified patients with schizophrenia or SPD.

Table 5.  Standardized canonical coefficients for predicting diagnosis from Minnesota Multiphasic Personality Inventory basic subscales
 Canonical coefficients
MMPI scale12
  1. First coefficient distinguished patients with schizophrenia and SPD from students.

  2. Second coefficient distinguished schizophrenic patients from SPD patients.

Sc− 0.98− 0.89
Si0.3− 0.63
D− 0.350.32
F0.190.58
Hs0.26− 0.003
Pa− 0.190.35
L− 0.10.37
Ma− 0.020.54

Prior probabilities were adjusted for initial group membership to calculate the accuracy of these coefficients in predicting group. As shown in Table 6, the resulting canonical function correctly classified 56.1% of schizophrenia, 55.6% of SPD and 98.1% of students with a combined correct classification rate of 90.3% (canonical r = 0.75, Wilks’ lambda = 0.408), χ2 (16, 622) = 22.008, P < 0.001.

Table 6.  Correct classifications of discriminant function analysis using the Minnesota Multiphasic Personality Inventory basic subscales
Actual group% of correct classificationSchizophrenia
P = 0.128
Predicted group
SPD
P = 0.056
Students
P = 0.816
Total
Schizophrenia56.123 5 13 41
SPD55.6 410 4 18
Students98.1 4 1257262
Total90.33116274321

The Harris-Lingoes and Serkownek subscales

A second discriminant function analysis was performed in an attempt to discriminate among groups of schizophrenia, SPD or students. Backward stepwise analysis was performed using the Harris-Lingoes and Serkownek subscales (20 scores) with a minimum F-value of 10.00 required to remove. The subscales in D, Pa, Sc and Si were selected because they were hypothesized as characteristics of schizotypy. Table 7 shows that the disciminant function analysis yielded two significant roots. The first coefficient, defined by positive weights on D4 (mental dullness) and Sc1 (social alienation) and a negative weight on Si (inferior-personal discomfort), distinguished the patients with schizophrenia and those with SPD from students. The second coefficient, defined by a negative weight on Sc3 (bizarre sensory experiences) and positive weights on Sc1 (social alienation) and Sc2 (emotional alienation), best identified patients with schizophrenia or SPD.

Table 7.  Standardized canonical coefficients for predicting diagnosis from Minnesota Multiphasic Personality Inventory Harris-Lingoes subscales
 Canonical coefficients
MMPI scale12
  1. D4, mental dullness; Sc1, social alienation; Sc2, emotional alienation; Sc6, bizarre sensory experiences; Si1, inferiority-personal discomfort.

D4 0.92− 0.11
Sc1 0.6 0.65
Sc2− 0.43 0.57
Sc6 0.36− 1.03
Si1− 0.63 0.16

Prior probabilities were adjusted for initial group membership to calculate the accuracy of these coefficients in predicting group. As shown in Table 8, the resulting canonical function correctly classified 48.8% of schizophrenia, 50.0% of SPD and 95.0% of students with a combined correct classification rate of 89.6% (canonical r = 0.65, Wilks’ lambda = 0.508), χ2 (10, 628) = 25.313, P < 0.001.

Table 8.  Correct classifications of discriminant function analysis using the Minnesota Multiphasic Personality Inventory Harris-Lingoes subscales
Actual group% of correct classificationSchizophrenia
P = 0.128
Predicted group
SPD
P = 0.056
Students
P = 0.816
Total
Schizophrenia48.820 4 17 41
Schizotypal disorder50 2 9 7 18
Students95 8 5249262
Total86.63018273321

DISCUSSION

The results of the present study are consistent with previous research reporting elevations in some clinical and validity scales (i.e. D, Pa, Pt, Sc and F) in patients with schizophrenia compared with normal control subjects18,19,21 (20 white patients,18 61% Caucasian, 36% African-American and 3% Asian-American of 33 patients,19 18 non-Hispanic Caucasian and one Hispanic of 19 patients21). This finding suggests that the specific feature of MMPI profile in patients with schizophrenia is culturally independent.

Moreover, we presented the MMPI profiles of patients diagnosed with SPD, which have not been reported by other investigators, unlike the case with non-clinical subjects.8–10 The present study suggests patients with schizophrenia have lower scales than SPD patients for obsessiveness-anxiety (Pt), social discomfort and social avoidance (Si). A high Pt scale generally represents obsessive–compulsive anxiety, irrational fears, highly strung, difficulty concentrating, and lack of self-confidence. Therefore, the results indicate SPD patients suffer from more distress and irrational struggles than schizophrenic patients. A high Si scale, on the other hand, represents social withdrawal associated with social discomfort and social anxiety, not withdrawal due to lack of interest in relating to others. Therefore, SPD patients are supposed to feel more social discomfort and practice more social avoidance compared with patients with schizophrenia. Furthermore, significantly higher scores were noted on subjective depression (D1), social alienation (Sc1), emotional alienation (Sc2) and lack of ego mastery, conative (Sc4) for SPD subjects compared to those with schizophrenia.

The two-point codetypes analysis revealed that 77.5% of the students, 11.1% of patients with SPD, and 14.3% of patients with schizophrenia did not produce any particular code. However, subsequent analyses showed that schizophrenic patients produced the two-point codetypes of 8-6, 2-6, 7-8 frequently, while SPD patients were more associated with those of 7-8, 2-7, 6-8. A total of 3.3% of students produced the two-point codetypes typical of schizophrenic or SPD patients. It was also found that 26.2% of schizophrenic patients, 44.4% of SPD patients and 1.1% of the students displayed the Moldin code. Thus, we identified schizophrenia-related codetypes of MMPI that were not included in the nine codes reported by Moldin et al.11 For instance, 9.5% of schizophrenic patients had the 6-2 codetype, and both 9.5% of schizophrenia and 16.7% of SPD patients had the 8-7 codetype, consistent with the suggestion by Merritt et al.10

The MMPI was found to be useful in discriminating subjects with schizophrenia from those with SPD or from the university students. The distribution of psychopathology demonstrated by the MMPI profiles suggests considerable overlap between schizophrenia and SPD. However, the discriminant function analysis revealed a subtle difference in the MMPI profiles between these two groups. The analysis of the MMPI basic scales showed that the Sc (schizophrenia) scale was the primary component to distinguish subjects with either schizophrenia or SPD from the students. Moreover, the second component separated schizophrenia from SPD, attributable to higher trends of Sc and Si in SPD, while schizophrenic patients had higher scores of F and Ma than SPD patients. These results suggest that SPD patients are more associated with unusual thinking and experiences (Sc), and social discomfort and distance (Si) than schizophrenic patients, while schizophrenic patients more often experience difficulty in inhibiting expression of illness (Ma), provide unusual response and have serious psychopathology (F). The discriminant function analysis using the Harris-Lingoes scale showed that the primary component discriminated schizophrenia and SPD patients from the students, and that both groups of patients have higher tendency towards mental dullness (D4) and social alienation (Sc1) than students. In addition, the second component separated SPD from schizophrenia by showing that SPD patients feel the lack of rapport both with other people (Sc1) and with themselves (Sc2) to a greater degree than do schizophrenic patients, and that schizophrenic patients have more bizarre sensory experiences (Sc6) than SPD patients. Deterioration of general function in addition to the presence of positive and negative symptoms is characteristic of schizophrenia. On the other hand, SPD patients are characterized by relatively intact general function and prominent discomfort in social relationships. The present results from the discriminant function analysis are consistent with clinical features of these schizophrenia-spectrum disorders. Several previous studies9–11 have shown characteristics of MMPI in normal people with schizotypal personality, and Moldin's codetype, typically 2-7-8, was frequent. Furthermore, the present findings have clarified a special feature of MMPI profile in patients with schizotypal disorder. The ICD-10 criteria for schizotypal disorder include prodromal schizophrenia as well as SPD. The difference observed between schizotypal disorder and schizophrenia could be regarded as the prerequisites for overt psychotic symptoms. Although low doses of medication may prevent overt psychotic symptoms, 18 patients with schizotypal disorder have not developed overt schizophrenic symptoms so far. However, follow-up studies are necessary to confirm our results, and especially to make clear the difference of the MMPI profile between prodromal schizophrenia and SPD.

It is important to note that there is variation in the MMPI profiles of schizophrenia depending on the subtypes and the state of the illness. Thus, Subotnik et al. reported that patients with deficit schizophrenia had lower scores in depression, emotional alienation with loss of judgement, suspiciousness, obsessiveness, anxiety, social discomfort, and social avoidance than did non-deficit patients.22 Moreover, patients during the psychotic state were shown to present higher scores of F, Pa, and Sc than patients during the remitted state.21 The present study did not include patients with schizophrenia during the remitted state. Most patients with schizophrenia in the present study received the MMPI test after medication. Furthermore, we did not divide patients with schizophrenia by subtype. It is likely that these mixed schizophrenic conditions (the state of the illness or subtypes) produced a counterbalance concerning the profiles of patients with schizophrenia regardless of the state or subtypes, which validates the comparison between schizophrenia and SPD reported here.

There are several limitations of the present study that should be taken into account. Five out of 262 (1.9%) students were classified into patients (either schizophrenia or SPD) by the discriminant function analysis. Although this indicates specificity fairly well, it is possible that a limited degree of personality deviation characteristics of schizophrenia or SPD is present in normal population.

The MMPI is a useful tool for identifying people, including university students, who have problems related to mental health. The results of the present study suggest that the MMPI also provides a window into the internal world of patients with either schizophrenia or SPD, for whom a standard clinical interview alone is not sufficient to grasp. Although the clinical and validity scales of the MMPI were found to be sensitive to general psychopathology characteristics of the psychotic groups, SPD was best distinguished by the specific patterns of elevations on the Harris-Lingoes subscales.

ACKNOWLEDGEMENTS

This study was supported by a Grant-in-Aid for Exploratory Research, 12871016 (DrMatsui) from the Ministry of Education, Science, Sports and Culture of Japan.

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