Journal of Personality Disorders, 28, 1-13, 2014 © 2014 The Guilford Press VALIDITY OF SCHIZOID PERSONALITY DISORDER CONSTRUCT HUMMELEN ET AL.

POOR VALIDITY OF THE DSM-IV SCHIZOID PERSONALITY DISORDER CONSTRUCT AS A DIAGNOSTIC CATEGORY Benjamin Hummelen, PhD, MD, Geir Pedersen, PhD, Theresa Wilberg, PhD, MD, and Sigmund Karterud, PhD, MD

This study sought to evaluate the construct validity of schizoid personality disorder (SZPD) by investigating a sample of 2,619 patients from the Norwegian Network of Personality-Focused Treatment Programs by a variety of statistical techniques. Nineteen patients (0.7%) reached the diagnostic threshold of SZPD. Results from the factor analyses indicated that SZPD consists of three factors: social detachment, withdrawal, and restricted affectivity/anhedonia. Overall, internal consistency and diagnostic efficiency were poor and best for the criteria that belong to the social detachment factor. These findings pose serious questions about the clinical utility of SZPD as a diagnostic category. On the other hand, the three factors were in concordance with findings from previous studies and with the trait model for personality disorders in DSM-5, supporting the validity of SZPD as a dimensional construct. The authors recommend that SZPD should be deleted as a diagnostic category in future editions of DSM-5.

This article was accepted under the editorship of Robert F. Krueger and John Livesley. From Department of Research and Development, Clinic of Mental Health and Addiction, Oslo University Hospital, Oslo, Norway (B. H., T. W.); The Norwegian Network of Personality-Focused Treatment Programs, Clinic of Mental Health and Addiction, Oslo University Hospital, Oslo, Norway (G. P.); Department of Personality Psychiatry, Clinic of Mental Health and Addiction, Oslo University Hospital, Oslo, Norway (B. H., S. K.); and University of Oslo, Institute of Clinical Medicine, Oslo, Norway (T. W., S. K.). We wish to thank the patients and staff from the following sixteen treatment units in the Norwegian Network of Personality-Focused Treatment Programs for their contribution to this study: Department for Personality Psychiatry, Oslo University Hospital; the Group Therapy Unit, Lillestrøm District Psychiatric Center, Akershus University Hospital; the Unit for Group Therapy, District Psychiatric Center, Lovisenlund, Sørlandet Hospital HF, Kristiansand; the Unit of Personality Psychiatry, Department of Mental Health, Sanderud, Innlandet Hospital Health Authority; the Group Therapy Unit, Outpatient Clinic, Drammen Psychiatric Center; the Unit for Group Therapy, Vestfold Mental Health Care Trust, Tønsberg; the Group Therapy Unit, Alna District Psychiatric Center, Akershus University Hospital; the Årstad Day Unit, Fjell & Årstad District Psychiatric Center, Bergen; the Bergenhus Day Unit, District Psychiatric Center, Bergen; the Unit for Group Therapy, Skien District Psychiatric Center, Telemark Hospital Health Authority; Day Treatment Unit, Furuset District Psychiatric Center, Aker University Hospital, Oslo; the Group Therapy Unit, Ringerike Psychiatric Center, Hønefoss; the Outpatient Clinic in Farsund, District Psychiatric Center, Farsund; the Unit for Group Therapy, Jessheim District Psychiatric Center, Akershus University Hospital HF; the Day unit for group therapy, KDPS-Department of adult psychiatry, Blefjell Hospital, Kongsberg and the Group treatment team, Psychiatric Outpatient Clinic, Ålesund. Address correspondence to Benjamin Hummelen, Department of Research and Development, Clinic of Mental Health and Addiction, Oslo University Hospital, PO Box 4959 Nydalen, 0424 Oslo, Norway; E-mail: [email protected]

1

2

HUMMELEN ET AL.

Schizoid personality disorder (SZPD) is the least studied among the 10 specific personality disorders (PDs) in DSM-IV (American Psychiatric Association [APA], 1994). The lack of empirical studies on SZPD was one of the reasons for the DSM-5 Task Force’s proposal to remove SZPD from the DSM system. However, SZPD was retained as a separate diagnostic category in the first edition of DSM-5 (APA, 2013). To justify the further continuation of SZPD as a diagnostic category, empirical studies should confirm the validity and clinical utility of this category. The paucity of scientific studies on SZPD is in contrast to the richness of the clinical literature during the 20th century. Fairbairn, Guntrip, and Millon and others have contributed to the development of this concept (Akhtar, 1987; Guntrip, 1952; Millon, 1996). Although a broad concept, SZPD includes common themes such as social withdrawal and constricted feelings. Meanwhile, interest in the schizoid personality waned after the publication of DSM-III (APA, 1980), in which the schizoid personality was split up into three categories: schizotypal PD, avoidant PD, and schizoid PD. The decision to differentiate between avoidant PD and schizoid PD was largely based on the assumption that persons with avoidant PD shun people because of feelings of inadequacy and embarrassment, whereas individuals with SZPD avoid people because of a lack of interest in human relationships (Millon, 1996). Within the same vein, some authors have contended that patients who were labeled “schizoid” actually fall into two distinct groups: an “affect constricted” group, who might better be subsumed within schizotypal PD, and a “seclusive” group, who might better be subsumed within avoidant PD (Triebwasser, Chemerinski, Roussos, & Siever, 2012). However, this issue has hardly been subjected to empirical investigation. In epidemiological studies based on DSM-III-R (APA, 1987) or DSM-IV (APA, 1994), prevalence estimates of SZPD in the general population range from 0% to 3.1% (Grant et al., 2005; Samuels et al., 2002; Torgersen, Kringlen, & Cramer, 2001). The large range in prevalence estimates is indicative of reliability problems. Zanarini et al. (2000) found that SZPD had the poorest reliability estimates of all PDs, and a recent clinical study found evidence for substantial false-positive rates of SZPD if only assessed at one point in time (Pedersen, Karterud, Hummelen, & Wilberg, 2013). Moreover, the low prevalence of SZPD in clinical samples suggests poor clinical utility as a psychiatric diagnosis. Of interest, the frequency of SZPD tends to be higher in community samples than in outpatient samples, in which prevalence rates usually do not exceed 1% (Zimmerman, Rothschild, & Chelminski, 2005). In a recent review of the SZPD construct, Triebwasser et al. (2012) outlined that SZPD occurs fairly frequently in clinical samples, referring to the study by Herpertz, Steinmeyer, and Sass (1994). However, this study included only inpatients, in which the schizoid traits might be due to the presence of other mental disorders. Among the nine patients with SZPD in the study by Herpertz et al. (1994), two were diagnosed with schizophrenia, two with organically induced psychic syndromes, and two with psychoactive substanceinduced disorders. Large variations in the presence of SZPD might also be related to differences in base rates of high-functioning autism spectrum disorders, mostly re-

VALIDITY OF SCHIZOID PERSONALITY DISORDER CONSTRUCT 3

ferred to as Asperger’s syndrome in the pre-DSM-5 era. Asperger’s syndrome was introduced relatively late in the official nomenclature (APA, 1994), and most epidemiological studies on PDs have not taken into account the existence of this disorder. It is assumed that there is a large overlap between the DSM-IV Asperger’s syndrome and SZPD, not least because one criterion of Asperger’s syndrome is similar to current descriptions of schizoid PD, that is, “a lack of spontaneous seeking to share enjoyment, interests or achievements with other people” (APA, 1994). On the other hand, it has been suggested that schizoid individuals are not so much unable to imagine how other people feel and think as unable to modify their own reactions to the meet the need of others (Wolff, 1991). Within the same vein, McWilliams (2011) asserted that schizoid people, despite their withdrawal, are more likely to be attuned to the subjective experiences of others than people with Asperger’s syndrome. In an older but central review of the SZPD construct, Kalus, Bernstein, and Siever (1993) discussed two essential issues: the relationship between SZPD and other PDs, and the relationship between SZPD and schizophrenia. The authors contended that the SZPD construct had improved substantially from DSM-III to DSM-III-R and proposed to continue the diagnosis after the implementation of some minor changes. Accordingly, from DSM-III-R to DSM-IV, the SZPD criteria were hardly changed. The most notable adjustment was the deletion of DSM-III-R Criterion 3 (“Rarely, if ever, claims or appears to experience strong emotions, such as anger and joy”) and the inclusion of a criterion describing anhedonia (“Takes pleasure in few, if any, activities”). It should be emphasized that the DSM-5 criteria are identical to those listed in DSM-IV. As far as we can see, after the publication of DSM-IV, only the NESARC study (National Epidemiologic Survey on Alcohol and Related Conditions) has published results on the psychometric properties and factor structure of the SZPD criteria (Harford et al., 2013). The authors conducted an item-response theory analysis of the DSM-IV PD criteria and found good item discrimination and threshold (difficulty/severity) of the SZPD criteria. This study also found that a one-dimensional model of SZPD had a better fit than a two-factor model. Another report from the NESARC, using taxometrics, found support for a latent dimensional rather than taxonic (latent categorical) structure of SZPD (Ahmed, Green, Buckley, & McFarland, 2012). This study assumed that SZPD had a two-dimensional structure, consisting of social withdrawal and emotional detachment. However, it is not clear on which empirical evidence this model was based, although it resembles the model of Millon (1996), who suggested that the two most prominent schizoid features are “unengaged interpersonal conduct” and “apathetic temperament.” In this study, we wanted to investigate aspects that pertain to the construct validity of the SZPD in a large clinical sample of patients with different types of PDs. In more detail, we wanted to investigate prevalence of SZPD, comorbidity patterns between SZPD and other PDs, psychometric properties of the SZPD criteria, and factor structure of the construct. In line with the study of Ahmed et al. (2012), we assumed that the SZPD criteria consist of two factors: social withdrawal and social detachment. However, we did not consider the empirical evidence for these factors strong enough to conduct

4

HUMMELEN ET AL.

only confirmatory factor analysis. Therefore, we conducted exploratory factor analysis first, followed by confirmatory factor analysis. METHODS PARTICIPANTS

The original sample consisted of 3,391 patients from the Norwegian Network of Personality-Focused Treatment Programs (Karterud et al., 2003), admitted to treatment from 1994 to 2005 and diagnosed according to DSMIV. Patients were referred from different clinical sites, including psychiatric inpatient and outpatient departments, general practitioners, and psychotherapists in private practice. Most patients were referred for assessment and treatment for PD, but a smaller number (10%) was referred for treatment of chronic, nonpsychotic symptom disorders, such as recurrent depressive disorder and anxiety disorders. To increase generalizability to other samples of PD patients, subjects without a PD diagnosis were excluded in this study (N = 772), resulting in a sample of 2,619 patients. Mean age was 34 (range 18–63, SD = 9), and 71% were females. Most patients (72%) had one PD diagnosis, 20% had two PD diagnoses, and 8% had three or more PD diagnoses. The prevalence of SZPD across the units ranged from 0% to 1.7%. An ANOVA test revealed no significant differences. Furthermore, the prevalence of SZPD appeared to be evenly distributed over the years. DIAGNOSTIC ASSESSMENTS

All units in this study complied with the diagnostic and data collection procedures required for membership in the Norwegian Network. Staff members were trained in PD diagnostics through attendance at local courses and Network conferences. DSM-IV diagnoses were established by way of the “Longitudinal, Expert, All Data” standard (LEAD standard; Pedersen et al., 2013). Tentative diagnoses were established at admission on the basis of referral letters, self-reported history and complaints, and two clinical structured diagnostic interviews: (a) the Mini-International Neuropsychiatric Interview for Axis I diagnoses (MINI; Sheehan et al., 1994), and (b) the Structured Clinical Interview for DSM-IV Personality Disorders (SCID-II; First, 1994). During the 18 weeks of day treatment, therapists could affirm or review diagnoses based on extensive knowledge from a variety of group observations. A final PD diagnosis required that the criteria from the original SCID-II protocol were confirmed by clinical observations. It is assumed that the LEAD procedure resulted in more valid diagnoses (Pedersen et al., 2013). A reliability test of the SCID-II interview at the Oslo unit gave acceptable interrater reliability estimates at admission of three common PD diagnoses (borderline, avoidant, and paranoid; Arnevik et al., 2009). However, the interrater reliability of SZPD was not tested.

VALIDITY OF SCHIZOID PERSONALITY DISORDER CONSTRUCT 5

STATISTICS

Chi-square statistics were used to evaluate the strength of association between SZPD and the other PDs, and between the SZPD criteria and the 10 specific PD diagnoses. Because only full criteria scores count in establishing the diagnosis, SZPD criteria were dichotomized by recoding subthreshold scores as not being present. Results are presented by phi coefficients, which is the Pearson correlation coefficient for dichotomous data. Yates’ corrected chi-square was applied in those cases where expected counts in cells were less than five. Diagnostic efficiency of the SZPD criteria was evaluated by sensitivity (Se), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV), and kappa coefficient (κ), described in detail by Streiner (2003). Having an SZPD diagnosis (i.e., fulfilling at least four criteria) was considered as the gold standard, and each criterion was evaluated against this gold standard. Thus, an SZPD criterion was considered true positive whenever a patient fulfilled the concerning criterion and had sufficient other criteria to reach the diagnostic threshold of SZPD. Internal consistency was evaluated by corrected item total correlations and Cronbach’s alpha (Cronbach, 1951). The total item correlation measures the strength of association of each SZPD criterion with the SZPD diagnosis, after controlling for autocorrelation (i.e., the correlation of the criterion with itself). Cronbach’s alpha was computed only for the nondichotomized SZPD criteria set. With regard to the factor analyses, it should be mentioned that many patients did not have any SZPD criteria at all. Therefore, to avoid null cells, patients without any SZPD criteria (threshold and subthreshold) were excluded from the factor analyses, leaving a sample of 1,739 patients. The original gradient scores of the SCID-II protocol were used in all factor analyses (i.e., 1 = criterion absent; 2 = subthreshold; and 3 = criterion present). At first, an exploratory factor analysis (EFA) was performed on all PD criteria except the juvenile criteria for antisocial PD. This analysis was performed in SPSS (Statistical Package for the Social Sciences, version 16 for Windows, 2007) using Principal Axis Factoring as the extraction method and Promax rotation with Kaiser normalization as the rotation method. Selection for further examination of the factors was based on eigenvalues (these should be higher than 1.0) and clinical coherence. As a control, a principal component analysis was conducted with varimax as the rotation method. After these analyses, the sample was split up at random into two subsamples, in order to conduct an EFA of the SZPD criteria on the first sample (n = 870) and a confirmatory factor analyses (CFA) on the second sample (n = 834), using Mplus (Muthén & Muthén, 1998–2010). For the EFA, promax was used as the rotation method (oblique rotation). Evaluation of the factors was based on eigenvalues, clinical coherence, and fit indices,that is, Chi Square Test of Model Fit (CST), Root-Mean-Square Error of Approximation (RMSEA), and Root Mean Square Residual (RMSR; Hu & Bentler, 1999). For CST, p values greater than .05 indicate good fit of the model. An RMSEA of .05 or below indicates a good fit, whereas values

6

HUMMELEN ET AL. TABLE 1. Personality Disorders in the Sample and Their Relationship to Schizoid PD Total

SZPD

(N = 2,691)

(N = 19) Phi

N

(%)

N

(%)†

Schizotypal

36

(1)

1

(5)

ns

Paranoid

316

(12)

7

(37)

.065 (p = .001)

Antisocial

56

(2)

1

(5)

ns

Borderline

741

(28)

4

(21)

ns

Histrionic

13

(0.2)

0

(0)

ns

Narcissistic

26

(1)

0

(0)

ns ns (p = .078)

Avoidant

1,265

(46)

13

(68)

Dependent

315

(12)

0

(0)

ns

Obsessive-Compulsive

270

(10)

5

(26)

.045 (p = .021)

Note. †The percentage of patients with SZPD who also had the concerning PD, e.g., 37% of the patients with SZPD also had paranoid PD.

between .05 and .08 indicate a reasonable fit. RMSR is recommended to be less than .05. Estimations were based on the Maximum Likelihood function. CFA was conducted to confirm that the best-fitting model of the EFA performed better than the other models. The models were evaluated by CST, RMSEA, Standardized Root Mean Square Residual (SRMSR), Akaike Information Criterion (AIC, small values indicate a good-fitting, parsimonious model), the Non-Normed fit index (NNFI, values greater than .90 are indicative of a good-fitting model), and comparative fit index (CFI, should be greater than .95; Hu & Bentler, 1999). Results PREVALENCE AND GENDER DISTRIBUTION

Among the 2,619 patients included in this study, 19 fulfilled criteria for a SZPD diagnosis (0.7%). Only histrionic PD was less common than SZPD (Table 1). The frequency of SZPD was significantly higher in male patients than in female patients (1.3% and 0.5%, respectively, p = .023). RELATIONSHIP WITH OTHER PDS

As shown in Table 1, SZPD was significantly associated with paranoid PD and obsessive-compulsive PD. Two SZPD patients had SZPD as the only PD diagnosis. There was no significant relationship between SZPD and schizotypal PD—only one patient had both diagnoses. Table 2 gives the correlations (phi coefficients) between the SZPD criteria and the 10 specific DSM-IV PDs. SZPD Criterion 1 (no desires for close relationships) and Criterion 6 (indifferent to praise or criticism) were most strongly correlated with the diagnosis itself. Three SZPD criteria were positively correlated with avoidant PD and one criterion (indifferent to praise or criticism) was negatively correlated with this PD.

.16 —

.26 .17 .13 .19

4. Takes pleasure in few, if any, activities

5. Lacks close friends/confidants other than first-degree relatives

6. Appears indifferent to praise or criticism of others

7. Shows emotional coldness, detachment, or flattened affectivity

—

—

—

.07

.08

—

.09

—

PA

.07

.06

—

—

—

—

AS

—

—

—

—

—

—

—

NA

—

—

—

—

—

—

—

BO

Personality Disorders*

—

—

—

—

—

—

—

HI

—

−.06

.10

—

.09

.10

—

AV

—

—

—

—

—

—

—

DEP

—

—

—

—

—

.10

—

OC

Note. *Only correlations with p ≤ .01 are given. †Corrected item total correlation. SZ = schizoid PD; ST = schizotypal; PA = paranoid; AS = antisocial; NA = narcissistic; BO = borderline; AV = avoidant; DEP = dependent; OC = obsessive-compulsive.

—

—

.06

.25 .20

2. Almost always chooses solitary activities

.23

1. Neither desires nor enjoys close relationships

3. No/little interest in having sexual experiences with another person

—

SZ†

Criteria

ST

TABLE 2. Correlations (Phi Coefficients) Between the SZPD Criteria and PD Diagnoses (N = 2,619)

VALIDITY OF SCHIZOID PERSONALITY DISORDER CONSTRUCT 7

8

HUMMELEN ET AL. TABLE 3. Diagnostic Efficiency Indices of the SZPD Criteria (N = 2,619) BR (%)

Se

Sp

PPV

NPV

κ

1. No desires for close relationships

1.3

.58

.99

.33

.99

.42

2. Solitary activities

10

.89

.90

.06

.99

.11

3. No interest in sexual experiences

9

.79

.91

.06

.99

.10

4. No pleasure in activities

8

.74

.86

.06

.99

.11

5. Lacks close friends

11

.79

.89

.05

.99

.08

6. Indifferent to praise or criticism

1.0

.32

.99

.24

.99

.27

3

.42

.97

.10

.99

.16

7. Flat affect

Note. BR = base rate; Se = sensitivity. Sp = specificity. PPV = positive predictive value; NPV = negative predictive value. κ = Cohen’s kappa.

PSYCHOMETRIC PROPERTIES

The prevalence (base rate) of the SZPD criteria varied from 1% to 11% (Table 3). In more detail, 590 patients had one SZPD criterion, 189 had two criteria, 60 had three, 13 had four, and six patients had five or six criteria. Within SZPD, the prevalence (= sensitivity) ranged from 32% (Criterion 6) to 89% (Criterion 2). Criterion 2 was quite common in other PDs as well, reducing the diagnostic efficiency. Criterion 6 (indifferent to praise or criticism) had the lowest prevalence within SZPD but had relatively high specificity and positive predictive value. Overall, Criterion 1 (no desires for close relationships) and Criterion 6 (indifferent to praise or criticism) had the best psychometric properties as indicated by high specificity, high positive predictive value, and high kappa. Criterion 7 (flat effect) performed also relatively well. Negative predictive power was large for all SZPD criteria due to the low prevalence of SZPD, which means that there were many true-negative— and few false-negative—cases. Cronbach’s alpha was .60 for the nondichotomous SZPD criteria set. FACTOR STRUCTURE

Exploratory factor analysis (EFA) including all PD criteria resulted in the extraction of 21 factors with eigenvalues larger than 1.00. The SZPD criteria loaded on four factors, Factors 8, 15, 17, and 21 (Table 4). Criterion 5 (lack of close friends) was part of Factor 8, which included one other criterion, the schizotypal criterion with the same content. One borderline PD criterion (chronic feelings of emptiness) also loaded on Factor 15. Initially, factor loadings lower than .30 were not considered. Lowering the threshold from .30 to .20, did not result in additional loadings on the SZPD factors. None of the SZPD criteria loaded higher than .20 on other factors. The two main SZPD factors appear to have good clinical coherence as they are in concordance with the factors of Ahmed et al. (2012), social withdrawal and emotional detachment. Principal component analysis gave an identical factor structure. EFA of the seven SZPD criteria resulted in the extraction of three factors with eigenvalues larger than 1.00. The three-factor model had better fit

VALIDITY OF SCHIZOID PERSONALITY DISORDER CONSTRUCT 9 TABLE 4. Principal Axis Factoring (Pattern Matrix) of all PD Criteria (N = 1,739) Factor 10

15

17

21

1. No desires for close relationships

—

—

.53

—

2. Solitary activities

—

—

.41

—

3. No interest in sexual experiences

—

—

—

.48

4. No pleasure in activities

—

.60

—

—

5. Lacks close friends

.86

—

—

—

6. Indifferent to praise or criticism

—

—

.35

—

7. Flat affect

—

.51

—

—

Schizotypal (8; no close friends)

.87

—

—

—

Borderline (7; chronic feelings of emptiness)

—

.33

—

—

Note. Only factors of relevance for SZPD are given. The total model explained 51 % of the variance. Factor 10 explained 2.1% of the variance; factor 15 explained 1.5%; factor 17 explained 1.4%, and factor 21 explained 1.3%. The model converged after 12 iterations.

indices than the one-factor and two-factor models (Figure 1). The first factor corresponds to Factor 17 in the previous factor solution, the second factor to Factor 10, and the third factor to Factor 15. However, Criterion 2 (solitary activities) had moved to a different factor and now loaded on the same factor as Criterion 5 (lacks close friends). Criterion 3 (no interest in sexual experiences) loaded slightly on Factor 1 (.20). Factor 1 correlated with both Factors 2 and 3. The latter factors did not correlate with each other. The results of the CFA confirmed that the three-model factor performed better than the one-factor model. Fit indices of the three-factor model were as follows: CST = 7.20 (df = 6, p value = .303), RMSEA = .015 (90% confidence interval [CI] [ .000, .049]), SRMSR = .019, AIC = 7241.4, CFI = .999, and NNFI = .998. The two-factor model did not converge within 1,000 iterations. Fit indices of the one-factor model were: CST = 142.6 (df = 9, p value = .000), RMSEA = .133 (90% CI [.115, .153]), SRMSR = .080, AIC = 7370.8, CFI = .909, and NNFI = .848. Because Criterion 3 (no interest in sexual experiences) had a loading of only.20 in the EFA, this criterion was not included in the CFAs. An additional CFA with Criterion 3 added to the first factor proved that this decision was correct. This model had poorer fit indices: CST = 30.7 (df = 11, p = .012), RMSEA = .046 (90% CI [ .027, .066]), SRMSR = .032, AIC = 7176.2, CFI = .987, and NNFI = .975. Clinical coherence of the three-factor solution appears to be good. The first factor reflects an indifferent attitude toward other people and can be called social detachment or, to be in line with DSM-5, intimacy avoidance. However, the latter concept does not cover the content very well because “indifference to praise or criticism” does not seem to be directly related to intimacy avoidance. The second factor is more a behavioral dimension and may be called withdrawal. The third factor reflects an affective dimension and was labeled restricted affectivity, although anhedonia is a good alternative.

10

HUMMELEN ET AL.

FIGURE 1. Three-factor solution according to exploratory factor analysis (N = 870). Note. Only patients with at least one threshold or subthreshold SZPD criterion were included in the analyses. Eigenvalues: Factor 1 =1.997; factor 2 = 1.397; factor 3 = 1.086. Interfactor correlations: factor 1–2 = .190, factor 1–3 = 0.363, and 2–3 = .090. Fit indices for the one-factor model were as follows: CST = 145.4 (df = 14, p value = .000), RMSEA = .104 (90% CI [ .089, .119]), and RMSR = .091. For the two-factor model: CST = 30.7 (df = 8, p value = .002), RMSEA = .057 (90% CI [.037, .079]), and RMSR = .037; For the three-factor model: CST = 1.17 (df = 3, p value = .76), RMSEA = .000 (90% CI [.000, .039]), and RMSR = .005.

DISCUSSION

The prevalence of SZPD was very low in this clinical sample of patients with different types of PDs (0.7%). SZPD was significantly associated with paranoid PD and obsessive-compulsive PD. In the factor analyses, three factors emerged: social detachment, withdrawal, and restricted affectivity/anhedonia. These factors replicate several facets of the detachment domain in the DSM-5 trait model for PDs, although there were some minor differences. Overall, the psychometric properties of the SZPD criteria were poor and somewhat better for criteria that belong to the social detachment factor,that is, “no desires for close relationships” and “indifference to praise and criticism.” The low prevalence of SZPD in this sample, as well as the finding that SZPD was seldom diagnosed as the only PD, is in line with findings from other studies (First et al., 2004; Fossati et al., 2000; Zimmerman, et al., 2005) and poses questions about the clinical utility of SZPD as a diagnostic category. Poor clinical utility was also reported by Zanarini et al. (2000), who found substantially poorer reliability estimates for SZPD than for the

VALIDITY OF SCHIZOID PERSONALITY DISORDER CONSTRUCT 11

other PDs. One may object that SZPD could be more reliably assessed by clinical observation than by diagnostic interviews (Kosson et al., 2008). However, in our sample, many patients who were initially diagnosed with SZPD lost this diagnosis during longitudinal assessment, and no new patients were added to the SZPD category (Pedersen et al., 2013). On the basis of these considerations, SZPD should be deleted as a diagnostic category in future editions of DSM-5. However, our findings support the validity of SZPD as a dimensional construct. First, the three SZPD factors were not related to any other PDs or PD criteria, with the exception of one borderline PD criterion (chronic feelings of emptiness criterion), which loaded modestly on the social detachment factor, and one schizotypal criterion (no close friends), which virtually is the same criterion as the fifth SZPD criterion. Even after lowering the threshold of factor loadings from .3 to .2, the SZPD factors were distinct from other PD criteria or factors. Second, our factor structure is in concordance with the section III trait model of DSM-5 (the alternative model for PDs, APA, 2013), that is, intimacy avoidance, withdrawal, and restricted affectivity. Our results deviate slightly from the section III trait model in two ways. First, the social detachment factor in our model does not converge entirely with the intimacy avoidance facet of DSM-5 as it also includes indifference toward others’ opinions. The term social detachment was derived from previous DSM-5 proposals, in which this facet still was part of the larger detachment domain (see Krueger, Derringer, Markon, Watson, & Skodol, (2012, for an explanation of the decision to merge social detachment and social withdrawal into one facet, i.e., withdrawal). Second, in DSM-5, anhedonia and restricted affectivity are considered as different facets of the detachment domain. Our findings suggest that anhedonia and restricted affectivity are similar constructs. The lack of association between SZPD and schizotypal PD may be due to selection bias. Patients with prominent schizoid and schizotypal features were probably considered too deviant by clinicians to be included in the program. In a previous publication, we have outlined that the schizotypal patients in our sample might be more closely related to borderline PD than to schizophrenia spectrum disorders, especially those patients who were characterized by cognitive-perceptual difficulties (Hummelen, Pedersen, & Karterud, 2012). Another explanation for the lack of association might be that SZPD and schizotypal PD are different expressions of the schizophrenia spectrum. SZPD may be more related to schizophrenia with predominantly negative features, whereas schizotypal PD may be more related to schizophrenia with positive features. The same concerns have been raised by Ahmed et al. (2012). A different explanation would take into account that schizoid PD may be related to autism spectrum disorders. Unfortunately, we were not able to investigate this issue any further in our sample because patients were not assessed by structural clinical interviews for autism spectrum disorders. With respect to the psychometric properties of the SZPD criteria, Criterion 1 (no desires for close relationships) clearly outperformed the other criteria (highest PPV and kappa), which is in line with the conclusions of

12

HUMMELEN ET AL.

Kalus et al. (1993), who found that this criterion demonstrated high sensitivity and specificity and was considered prototypical by clinicians. Criterion 6 (indifferent to praise and criticism) ranked second in our study but took an intermediate position in Kalus et al.’s review. Criterion 2 (solitary activities) was the most common criterion among SZPD patients, but because of its high prevalence in other PDs, it was less specific for SZPD. Criterion 3 (no interest in sexual activities) and Criterion 5 (lacks close friends) performed poorest according to the diagnostic efficiency indices. Indeed, these criteria do not reappear as separate facets in section III of DSM-5. The main limitation of the present study is the uncertainty with respect to the representativeness of the sample. First, patients were referred to treatment programs dominated by group psychotherapies, which may have resulted in an artificially low prevalence of SZPD because schizoid individuals may be even more reluctant to enter group therapy than individual therapy. However, a prevalence of .6% is not very deviant from the prevalence of other outpatient samples. Second, SZPD patients in this sample may not be representative of SZPD patients in the general population. The fact that SZPD patients in this study were referred to psychotherapeutic treatment may imply the recruitment of SZPD patients with higher levels of personality functioning than the average SZPD patient. In conclusion, the low prevalence of SZPD and the poor psychometric properties of the defining criteria pose serious questions about the clinical utility of this category. However, results of the factor analyses indicated that SZPD has good validity as a dimensional construct. Three factors came to the fore: social detachment, withdrawal, and restricted affectivity/anhedonia. These factors were clinically meaningful, were distinct from other factors, did replicate previous proposals, and were in line with the trait model in DSM-5. We suggest that SZPD should be discontinued as a separate PD category. References Ahmed, A. O., Green, B. A., Buckley, P. F., & McFarland, M. E. (2012). Taxometric analyses of paranoid and schizoid personality disorders. Psychiatry Research, 196(1), 123– 132. Akhtar, S. (1987). Schizoid personality disorder: A synthesis of developmental, dynamic, and descriptive features. American Journal of Psychotherapy, 41(4), 499–518. American Psychiatric Association. (1980). Diagnostic and statistical manual of mental disorders (3rd ed.). Washington, DC: Author. American Psychiatric Association. (1987). Diagnostic and statistical manual of mental disorders (3rd ed. rev.). Washington, DC: Author. American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4th ed.). Washington, DC: Author.

American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Washington, DC: Author. Arnevik, E., Wilberg, T., Urnes, O., Johansen, M., Monsen, J. T., & Karterud, S. (2009). Psychotherapy for personality disorders: Shortterm day hospital psychotherapy versus outpatient individual therapy—A randomized controlled study. European Psychiatry, 24(2), 71–78. Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16(3), 297–334. First, M. B. (1994). Structured clinical interview for DSM-IV Axis II personality disorders (SCID II). New York, NY: New York State Psychiatric Institute. First, M. B., Pincus, H. A., Levine, J. B., Williams, J. B. W., Ustun, B., & Peele, R. (2004).

VALIDITY OF SCHIZOID PERSONALITY DISORDER CONSTRUCT 13 Clinical utility as a criterion for revising psychiatric diagnoses. American Journal of Psychiatry, 161(6), 946–954. Fossati, A., Maffei, C., Bagnato, M., Battaglia, M., Donati, D., Donini, M., . . . & Prolo, F. (2000). Patterns of covariation of DSM-IV personality disorders in a mixed psychiatric sample. Comprehensive Psychiatry, 41(3), 206–215. Grant, B. F., Hasin, D. S., Stinson, F. S., Dawson, D. A., Chou, S. P., Ruan, W. J., & Huang, B. (2005). Co-occurrence of 12-month mood and anxiety disorders and personality disorders in the US: Results from the National Epidemiologic Survey on Alcohol and Related Conditions. Journal of Psychiatric Research, 39(1), 1–9. Guntrip, H. (1952). A study of Fairbairn’s theory of schizoid reactions. British Journal of Medical Psychology, 25(2–3), 86–103. Harford, T. C., Chen, C. M., Saha, T. D., Smith, S. M., Hasin, D. S., & Grant, B. F. (2013). An item response theory analysis of DSM-IV diagnostic criteria for personality disorders: Findings from the National Epidemiologic Survey on Alcohol and Related Conditions. Personality Disorders: Theory, Research, & Treatment, 4(1), 43–54. Herpertz, S., Steinmeyer, E. M., & Sass, H. (1994). “Patterns of comorbidity” among DSMIII-R and ICD-10 personality disorders as observed with a new inventory for the assessment of personality disorders. European Archives of Psychiatry and Clinical Neuroscience, 244(3), 161–169. Hu, L., & Bentler, P. (1999). Cutoff criteria for fit indexes in covariance structure analysis: Conventional criteria versus new alternatives. Structural Equation Modelling, 6(1), 1–55. Hummelen, B., Pedersen, G., & Karterud, S. (2012). Some suggestions for the DSM-5 schizotypal personality disorder construct. Comprehensive Psychiatry, 53(4), 341–349. Kalus, O., Bernstein, D., & Siever, L. (1993). Schizoid personality disorder: A review of current status and implications for DSMIV. Journal of Personality Disorders, 7(1), 43–52. Karterud, S., Pedersen, G., Bjordal, E., Brabrand, J., Friis, S., Haaseth, O., & Urnes, O. (2003). Day treatment of patients with personality disorders: Experiences from a Norwegian treatment research network. Journal of Personality Disorders, 17(3), 243–262. Kosson, D. S., Blackburn, R., Byrnes, K. A., Park, S., Logan, C., & Donnelly, J. P. (2008). Assessing interpersonal aspects of schizoid personality disorder: Preliminary validation

studies. Journal of Personality Assessment, 90(2), 185–196. Krueger, R., Derringer, J., Markon, K. E., Watson, D., & Skodol, A. E. (2012). Initial construction of a maladaptive personality trait model and inventory for DSM-5. Psychological Medicine, 42, 1879–1890. McWilliams, N. (2011). Psychoanalytic diagnosis. Understanding personality structure in the clinical process (2nd ed.). New York, NY: Guilford Press. Millon, T. (1996). Disorders of personality: DSMIV and beyond. New York, NY: Wiley. Muthén, L. K., & Muthén, B. O. (1998–2010). Mplus user’s guide, 6th edition. Retrieved from https://www.statmodel.com/ Pedersen, G., Karterud, S., Hummelen, B., & Wilberg, T. (2013). The impact of extended longitudinal observation on the assessment of personality disorders. Personality and Mental Health, 7(4), 277–287. Samuels, J., Eaton, W. W., Bienvenu, O. J., Brown, C. H., Costa, P. T., & Nestadt, G. (2002). Prevalence and correlates of personality disorders in a community sample. British Journal of Psychiatry, 180(6), 536–542. Sheehan, D. V., Lecrubier, Y., Janavs, J., Knapp, E., Weiller, E., & Bonora, L. I. (1994). MiniInternational Neuropsychiatric Interview (MINI). Tampa, FL, and Paris, France: University of South Florida Institute for Research in Psychiatry and INSERM-Hôpital de la Salpétrière. Streiner, D. L. (2003). Diagnosing tests: Using and misusing diagnostic and screening tests. Journal of Personality Assessment, 81(3), 209–219. Torgersen, S., Kringlen, E., & Cramer, V. (2001). The prevalence of personality disorders in a community sample. Archives of General Psychiatry, 58(6), 590–596. Triebwasser, J., Chemerinski, E., Roussos, P., & Siever, L. J. (2012). Schizoid personality disorder. Journal of Personality Disorders, 26(6), 919–926. Wolff, S. (1991). ‘Schizoid’ personality in childhood and adult life. I: The vagaries of diagnostic labelling. British Journal of Psychiatry, 159, 615–620. Zanarini, M. C., Skodol, A. E., Bender, D., Dolan, R., Sanislow, C., Schaefer, E., & Gunderson, J. G. (2000). The Collaborative Longitudinal Personality Disorders Study: Reliability of Axis I and II diagnoses. Journal of Personality Disorders, 14(4), 291–299. Zimmerman, M., Rothschild, L., & Chelminski, I. (2005). The prevalence of DSM-IV personality disorders in psychiatric outpatients. American Journal of Psychiatry, 162(10), 1911–1918.