The Personality Disorder Screening - Karger Publishers

Original Article · Originalarbeit (English Version of) Verhaltenstherapie 2011;21:154–161 DOI: 10.1159/000329747

Published online: Aug. 2011

Development of a Screening Measure for the Assessment of Personality Disorders: The Personality Disorder Screening – Short Version (PSS-K) Henning Schöttkea Julia Langea Mario Imholzb Karl Heinz Wiedla a b

Outpatient Psychotherapy Clinic, Institute of Psychology, Clinical Psychology and Psychotherapy, University of Osnabrück, Ameos Clinical Centre, Osnabrück, Germany

Keywords Personality disorders · Assessment · Screening · SCID-II

Schlüsselwörter Persönlichkeitsstörungen · Diagnostik · Screening · SKID-II

Summary Background: The assessment of personality disorders should be routine in psychotherapeutic treatment settings. This report describes a new screening measure which could be used as a screening tool in the first step of a two-stage diagnostic process for personality disorders: the Personality Disorder Screening – Short Version (PSS-K). Patients and Method: To validate the instrument, a non-clinical sample (n = 392), prisoners (n = 48), and 3 clinical samples, i.e., patients with substance abuse (n = 90), psychotherapeutic outpatients (n = 43), and psychiatric inpatients (n = 52), were recruited. The Structured Clinical Interview for DSM-IV Personality Disorders (SCID-II) was used as the gold standard. Results: The PSS-K appears to be a suitable screening instrument for personality disorders. The non-clinical sample differed significantly from the other subsamples. The items of the PSS-K and the PSS-K score show good convergent validity with the SCID-II questionnaire scores. Using receiver operating characteristic (ROC) analysis, a cut-off value of >4 on the screening measure correctly identified the presence of at least one personality disorder in 93% of cases. Conclusion: Considering the first results, the PSS-K seems to be a reliable and valid screening tool.

Zusammenfassung Hintergrund: Die Diagnostik von Persönlichkeitsstörungen sollte fester Bestandteil klinischer Eingangsuntersuchungen sein. In der vorliegenden Arbeit wird mit dem Persönlichkeitsstörungs-Screening – Kurzform (PSS-K) ein Screening-Fragebogen vorgestellt, der im sogenannten zweistufigen Diagnostikprozess im ersten Schritt zur «Schnellerkennung» einer Persönlichkeitsstörung eingesetzt werden kann. Patienten und Methode: Zur Validierung wurden eine nichtklinische Kontrollstichprobe aus der Normalbevölkerung (n = 392), Insassen einer Justizvollzugsanstalt (n = 48) und 3 klinische Stichproben rekrutiert: Patienten mit Substanzmissbrauch (n = 90), ambulante Psychotherapiepatienten (n = 43) und stationäre Psychiatriepatienten (n = 52). Das SKID-II (Structured Clinical Interview for DSM-IV Personality Disorders) diente bei der Validierung als Goldstandard. Ergebnisse: Das PSS-K erwies sich als reliabel und konstruktvalide. Die Probanden aus der Normalbevölkerung unterscheiden sich von den Testpersonen der anderen Stichproben. Die konvergente Validität der PSS-K-Items und der PSS-K-Summe mit den Fragebogen-Scores des SKID-II ist gegeben. Laut Receiver Operating Characteristic (ROC)-Analyse wird bei einem Cut-off-Wert von >4 in 93% der Fälle das Vorliegen mindestens einer Persönlichkeitsstörung richtig erkannt. Schlussfolgerung: Die Reliabilität und Validität des PSS-K konnte mit ersten Ergebnissen belegt werden.

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Accessible online at: www.karger.com/ver

Prof. Dr. Henning Schöttke Universität Osnabrück, Institut für Psychologie Klinische Psychologie und Psychotherapie, Poliklinische Psychotherapieambulanz Knollstr. 15, 49069 Osnabrück, Germany Tel. +49 541 9694-757, Fax -028 [email protected]

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Introduction The prevalence of a personality disorder (PD) in the general population is between 7 and 15% [Johnson et al., 2008]. In clinical treatment settings, this diagnosis is assigned in 45– 66% of cases [Thuo et al., 2008]. It is thus common (13–81%) to observe comorbidity of PD with symptomatic disorders from the Diagnostic and Statistic Manual of Mental Disorders (DSM; the so-called Axis I disorders) [Dolan-Sewell et al., 2001]. The presence of a PD may adversely affect the course of treatment of an Axis I disorder [Kasen et al., 2007; Newton-Howes et al., 2006; for an exception, see Fricke et al., 2003]. Therefore, a reliable and valid diagnostic for PD should be an integral part of the initial clinical-psychometric examination. Even if the subsequent treatment only deals with the symptomatic disorder, the patient’s PD-specific interaction criteria can hinder symptom-oriented therapy. Questionnaires for PD diagnostics include, e.g., the Millon Clinical Multiaxial Inventory (MCMI) [Millon et al., 1997] and the Personality Disorder Questionnaire-4 (PDQ-4) [Hyler, 1994]. There are also interview procedures for PD diagnostics, e.g., the International Personality Disorder Examination (IPDE) [Loranger, 1999], the Structured Clinical Interview for DSM-IV Personality Disorders (SCID-II) [First et al., 1995], and the Structured Interview for DSM Personality-IV (SIDP-IV) [Pfohl et al., 1995]. In German-speaking countries, the International Diagnosis Checklist for Personality Disorders (IDCL-P) is also used [Bronisch et al., 1995]. The aforementioned interviews cover at least the criteria for PD presented in the DSM (versions III and IV), and, because of their highly structured nature, facilitate a differentiated analysis of these disorders. In German-speaking countries, the SCID-II is the current gold standard for the diagnosis of a PD. These instruments are, however, very comprehensive, time-consuming, and require well-trained personnel, making their use in the diagnostic process very time- and cost-intensive. A remedy for this lack of a standard clinical-psychological diagnostic could be found, in our view, if the diagnosis of PD is made adaptively and, if necessary, in two stages [Mann et al., 1999]: The first step is a short, valid screening method which indicates whether there is enough evidence of a PD. This is similar to the requirement of the DSM-IV or ICD-10 (International Classification of Diseases), that the general criteria for the existence of a PD must be met before the diagnosis is further specified [Fiedler, 2001]. Only then, if necessary, would a second step, with a structured interview procedure and/or an additional questionnaire, verify the suspected diagnosis and make it more specific, where appropriate. This effective approach could improve the standard clinical diagnostics. Screening Procedures for Personality Disorders The first tests for quick detection of a PD in the diagnostic process used the total score on a questionnaire (e.g., PDQ) or

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Verhaltenstherapie 2011;21:154–161

the screening questionnaire that precedes the SCID-II interview [Langbehn et al., 1999]. The sensitivity of these as screening instruments is between 0.35 and 1.00; the specificity is 0.43–0.94 [Langbehn et al., 1999]. These questionnaires are very long, however, and therefore time-consuming to use, so they are not suitable for a short screening process as the first step of the two-stage diagnostic process. Short interviews were then developed, which are so far only available and verified in English, in which specific items from the above-mentioned interview were compiled into a brief screening interview [Morse and Pilkonis, 2007]. Among these short interviews are the Iowa Personality Disorder Screen (IPDS) [Langbehn et al., 1999], the Rapid Personality Assessment Schedule (PAS-R) [Van Horn et al., 2000], the Standardized Assessment of Personality Abbreviated Scale (SAPAS) [Moran et al., 2003], and an interview that was developed on the basis of 15 DSM criteria [Nurnberg et al., 2000]. The sensitivity of these screening interviews is between 0.64 and 0.94, the specificity between 0.79 and 0.85. Furthermore, there is a short questionnaire in the Inventory of Interpersonal Problems (IIP-PD), consisting of 28 items [Pilkonis et al., 1996], which is used in screening for PD (sensitivity 0.71–0.91, specificity 0.40–0.67). The drawbacks are that either no verified German versions are available, the short versions are still too long, or the psychometric parameters of the process result in too many incorrect classifications. In this study, we present a new screening questionnaire, the short form of the Personality Disorder Screening (PSS-K) (fig. 1). The goal is to make available a short, German-language, economically feasible, and sensitive screening instrument. Based on the PSS-K total score, the first step of an optimized diagnostic process, analogous to the verification of the general criteria for a PD in the DSM-IV and ICD-10, is to assess whether a second step is indicated in order to achieve a subsequent differentiated diagnosis. The following describes the test development of the PSS-K and the validation of the construct according to the SCID-II. A cut-off value is also determined, such that persons diagnosed with a PD according to SCID-II are optimally distinguished from healthy individuals.

Methods The PSS-K is based on a questionnaire for dimensional diagnosis of personality styles and disorders, the Personality Self-Portrait (PSP), developed by Oldham and Morris [1990, 2008]. The Personality Disorder Screening (PSS) was developed from a German translation of the PSP of Oldham and Morris [1992], at the Outpatient Psychotherapy Clinic of the University of Osnabrück. Data on quality criteria of the German and English versions of the PSP are not yet available. Only 10 of the original 13 PSP scales were used to develop the PSS. The corresponding scales of the 10 personality disorders of DSM-IV were considered. 10 items from each of the 10 scales were selected as representative of each PD – those which had the highest selectivity to the corresponding PSP subscale. With the goal of developing the shortest possi-

Schöttke/Lange/Imholz/Wiedl

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Name/Code:____________________________________________ The Questionnaire for Personality Disturbance Screening – Short Form (PSS-K). Please read through each statement. Please check the box with the characterization that best applies to you.

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Some statements consist of two parts. If you only agree with one part, please check Maybe; if you agree with both parts, please check Yes. Please do not omit any statement, even if you believe that it does not apply to you or the circumstances of your life; please respond as if it did apply. No. 1

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I can be impatient; I usually want to get what I want immediately.

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I generally have very intense relationships, and usually my feelings for a person vary from one extreme to the other. Sometimes I practically worship him, and then I can’t stand him.

첸

첸

첸

I am not very trusting, although I would like to be. I’m just afraid that people might take advantage of me if I’m not careful.

첸

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I tend to be a loner, and that’s fine with me. It’s no fun for me to be with other people a lot, even my family.

첸

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I’m very insecure. I often feel that people are looking at me and sizing me up, not always in a flattering way.

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첸

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I would rather stick to my usual daily routine than to venture into unfamiliar surroundings and situations.

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I am fascinated by a kind of underground life in which one can break the rules and get away with it.

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5

6

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Fig. 1. The Questionnaire for Personality Disturbance Screening – Short Form (PSS-K). This translation of the questionnaire is not validated.

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I worry a lot that people I like are going to abandon me, even though there is usually no reason for this fear.

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The Personality Disorder Screening – Short Version (PSS-K)



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ble instrument, the first screening version was reduced, in a second step, to a short form with 8 items (PSS-K). Items with the highest effect size were selected, calculated according to the method of Hedges and Olkin [1985, cited by Rustenbach, 2003], which made the best differentiation between the presence or absence of at least one PD, diagnosed according to the SCID-II. The remaining items represent the scales of dependent (PSS-K1), histrionic (PSS-K2), borderline (PSS-K3), paranoid (PSS-K4), schizoid (PSS-C5), schizotypal (PSS-K6), obsessive/compulsive (PSS-K7), and antisocial (PSS-K8). The item scores of possible answers (no = 0, maybe = 1, yes = 2) are added to the PSS-K total score. The validation of the PSS-K construct was performed using the SCIDII [Fydrich et al., 1997]. The SCID-II is a two-stage process, consisting of a questionnaire with 119 items and an interview. Each item answered with ‘yes’ is further explored in the subsequent interview and evaluated as to whether the criteria for a PD are met. In this study, the dimensional questionnaire score (QS) of the SCID-II was used to validate the PSS-K. The reliability and validity of the SCID-II are described as good; for a detailed presentation, refer to Smith et al. [2003].

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36.5 31.9 31.4 0.3 3.75 (2.8)

M = mean, SD = standard deviation, Norm = general population, JVA = prison, Sub = substance dependence, Out = outpatient psychotherapy patients, In = inpatient psychiatric patients, n.s. = not significant. ***p < 0.01.

7.92 (3.6)

F(4.620) = 49.13***

30.2 32.1 34.4 3.2 5.08 (3.6) r2(12) = 127.72*** 26.9 46.2 26.9

17.8 26.7 48.9 6.7 7.51 (3.8) 7.7 20.5 43.6 28.2 6.54 (3.5)

23.2 39.5 32.6 4.7 7.00 (3.3)

40 (12.2) 39.7/60.3 F(4.611) = n.s. r2(4) = 125.56 *** 38.7 (13.1) 53.8/46.2 36.4 (10.1) 69.8/30.2 37.4 (10) 0/100 36.7 (9.4) 0/100 40 (12.9) 48.5/51.5

Age in years, M (SD) Women/men, % Education, % Baccalaureate Intermediate secondary school Secondary general school No completion PSS-K total score, M (SD)

Sub (n = 90) Norm (n = 392) Sample

JVA (n = 48)

Out (n = 43)

In (n = 52)

Test statistic

Total (n = 625)

Item

Table 1. Description of the samples and testing for differences in the subsamples

Samples The present study encompasses a variety of samples obtained from various research projects [Schöttke, 2006]. The experimental protocol was approved by the ethics officer of the institute. The subjects were informed about the study and participated voluntarily. We studied a total of 625 persons. In addition to volunteers from the general population, clinical samples and others were recruited, either because there was assumed to be a high prevalence of PD in that sample, or because the diagnosis of a PD might be of interest for therapeutic reasons or forensic psychiatric examination. The non-clinical samples are composed of an unselected sample of the general population (n = 392) and a sample of prisoners from a correctional facility (JVA; n = 48) [on the significance of PD in prisoners, see Frädrich and Pfäfflin, 2000]. In selecting the sample from the general population, only those were included who had filed no claim for psychotherapeutic or psychopharmacological treatment over the past year. The prisoners in the sample were, on average, sentenced to a term of 3.9 years (standard deviation (SD) = 2.46 years). Among the most common crimes were assault or homicide (n = 12), burglary, theft, or robbery (n = 9), and sexual offenses (n = 8). The clinical samples comprised patients with substance abuse disorders (especially illegal drugs and alcohol), who were in the hospital for detoxification (n = 90) [on the importance of PD among drug users, see Hesse et al., 2008], patients at the Outpatient Psychotherapy Clinic of the University of Osnabrück (n = 43), and patients from a specialized psychiatric hospital (n = 52) [on the importance of PD in the psychiatric and psychotherapeutic domain, see Lamont and Brunero, 2009; Samuels et al., 2002]. A copy of the explanatory statement signed by the patients or prison inmates was placed in the patient or prison files. Table 1 gives an overview of age, gender distribution, and educational achievement in the overall sample and the subsamples. The subsamples differ in gender distribution and educational attainment. There are also significant differences for the PSS-K total score in the subsamples. The sample from the normal population has the lowest value, and that from the psychiatric hospital has the highest. The sample from the normal population has descriptively the highest level of education, the prison sample the lowest. The main diagnoses in the sample of outpatient psychotherapy patients, according to the ICD-10, consist of affective disorders (F3X; 55.8%), neurotic, stress-related, and somatoform disorders (F4X; 55.8%), and eating disorders (F50.X; 16.3%). The patients present with an average of 1.63 disorder diagnoses. The sample of inpatient psychiatric patients shows the following main diagnoses, according to the ICD-10: affective disorders (F3X; 71.2%), neurotic, stress-related, and somatoform disorders (F4X; 19.2%), and eating disorders (F50.X; 7.7%). These patients have an average of 1.73 disorder diagnoses. The group of addicted patients consisted of n = 40 patients with multiple drug dependence (ICD-10: F19.2), n = 40 patients with alcohol dependence (ICD-10:

Tab

1

2

3

4

5

6

7

8

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Table 2. Item parameters in the various subsamples and in the total sample Item (PSS-K)

1

2

3

4

5

6

7

8

M (SD) Pi rit M (SD) Pi rit M (SD) Pi rit M (SD) Pi rit M (SD) Pi rit M (SD) Pi rit M (SD) Pi rit M (SD) Pi rit

Sample Norm (n = 392)

JVA (n = 48)

Sub (n = 90)

Out (n = 43)

In (n = 52)

Total (n = 625)

0.4 (0.7) 21 0.4 1.0 (0.9) 48 0.1 0.4 (0.7) 20 0.4 0.4 (0.7) 20 0.4 0.3 (0.6) 15 0.3 0.3 (0.6) 15 0.4 0.7 (0.8) 34 0.3 0.3 (0.6) 15 0.1

1.0 (1.0) 48 0.3 1.2 (0.9) 60 0.2 0.5 (0.8) 24 0.4 1.5 (0.7) 76 0.3 0.6 (0.8) 30 0.2 0.7 (0.9) 36 0.4 0.5 (0.8) 26 0.4 0.5 (0.8) 26 0.4

1.2 (0.9) 58 0.5 1.3 (0.9) 67 0.4 0.9 (0.9) 47 0.4 1.0 (0.9) 56 0.4 0.7 (0.8) 36 0.4 0.7 (0.8) 34 0.5 0.6 (0.8) 32 0.3 0.9 (0.8) 46 0.1

1.3 (0.8) 63 0.4 1.2 (0.9) 62 0.4 0.7 (0.9) 34 0.2 1.1 (0.9) 57 0.5 0.4 (0.6) 22 0.2 0.9 (0.9) 47 0.3 1.0 (0.8) 50 0.3 0.3 (0.6) 16 0.1

1.2 (0.9) 61 0.3 1.3 (0.8) 64 0.4 0.9 (0.8) 42 0.3 1.1 (0.8) 53 0.4 0.8 (0.9) 38 0.3 1.2 (0.9) 61 0.7 1.1 (0.9) 56 0.3 0.4 (0.8) 21 0.1

0.7 (0.9) 35 0.5 1.1 (0.9) 54 0.3 0.5 (0.8) 27 0.4 0.7 (0.8) 36 0.5 0.4 (0.7) 22 0.4 0.5 (0.8) 25 0.5 0.7 (0.8) 36 0.3 0.4 (0.7) 21 0.2

Norm = general population, JVA = prison, Sub = substance dependence, Out = outpatient psychotherapy patients, In = inpatient psychiatric patients, M = Mean, SD = standard deviation, Pi = difficulty, rit = selectivity.

F10.2), and n = 10 patients who, in addition to alcohol dependence, were dependent on at least one illegal drug (ICD-10: F10.2 and F1X.2). All 625 persons whose data were used in this study took the PSS-K. The data of the samples from the normal population, the prison inmates, and the addicted patients were used for the test development and standardization; the subsequent validation was done using SCID-II, with the outpatient psychotherapy and psychiatric patients.

Results Distribution Characteristics and Reliability Table 2 presents the averages, standard deviations, difficulties, and selectivity of the PSS-K items for the subsample and the total sample. Considering first the difficulty of the items, PSS-K items 5 and 8 are the most difficult, and PSS-K item 2 is the easiest. The selectivities are largely satisfactory, with the exception of PSS-K item 8, in which selectivity is almost negligible across the samples. The internal consistency of the PSS-K is _ = 0.69 for the total sample. The reliabilities of the subsamples vary according to the number of subjects studied (general population _ = 0.58; prison inmates _ = 0.63; addicted patients _ = 0.68; outpatient psychotherapy patients _ = 0.60; inpatient psychiatric patients _ = 0.64).



Validity The inter-correlations of the PSS-K items are presented in table 3. PSS-K items 1, 4, and 6 have very high correlations among them. The correlations of the remaining items are in the low to medium range. Average inter-item correlation amounts to r_ = 0.21 (Fisher’s z-transformation). Convergent Validity Those in the sample of outpatient psychotherapy patients and inpatient psychiatric patients (n = 95) had the following prevalences of individual PDs, according to the SCID-II interview: avoidant (31.6%), obsessive/compulsive (14.7%), borderline (11.6%), paranoid (6.3%), dependent (4.2%), histrionic (4.2%), narcissistic (4.2%), negativistic (3.2%), antisocial (3.2%), schizotypal (2.1%), and schizoid (1.1%). In total, 56.8% of the patients have at least one comorbid PD. This patient sample has an average of 1.14 diagnoses of PD. Each item of the PSS-K correlates between 0.22 and 0.4 (all p values < 0.05) with the number of PDs in the SCID-II (table 3). The PSS-K total and the number of PDs are correlated at 0.53 (p < 0.01). Further, there are significant bivariate correlations (all p values < 0.01) between the PSS-K total and all of the QSs on the SCID-II (0.34 < r > 0.56), with the excep-


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Table 3. Inter-correlation of the items of the PSS-K (n = 625) and correlation with the number of personality disorders according to SCID-II (n = 95, samples In, Out)

PSS-K1 PSS-K2 PSS-K3 PSS-K4 PSS-K5 PSS-K6 PSS-K7 PSS-K8

PSS-K1

PSS-K2

PSS-K3

PSS-K4

PSS-K5

PSS-K6

PSS-K7

PSS-K8

SCID-II

1.00

0.21** 1.00

0.35** 0.25** 1.00

0.46** 0.15** 0.28** 1.00

0.17** 0.13** 0.11** 0.31** 1.00

0.40** 0.21** 0.25** 0.43** 0.34** 1.00

0.21** 0.05 0.11** 0.25** 0.25** 0.29** 1.00

0.11** 0.15** 0.24** 0.10* 0.18** 0.11** −0.07 1.00

0.23* 0.32** 0.27** 0.24* 0.25* 0.40** 0.28** 0.22*

The ing in th T esti bach be c relia num the test bru wou Kel stru hete sma bru relia tenc do i ana ther SAP _= liab stud add (SC and num SCI leas to p sub

** p < 0.01. * p < 0.05. Out = outpatient psychotherapy patients; In = inpatient psychiatric patients.

Table 4. Quality criteria for possible cut-off values (n = 95, samples In, Out)

Cut-off value

Sens

Spec

Youden Index

PPV

NPV

>0 >1 >2 >3 >4 >5 >6 >7 >8 >9 > 10 > 11 > 12 > 13 > 14

1 1 1 0.98 0.93 0.87 0.80 0.74 0.59 0.48 0.33 0.17 0.07 0.04 0.02

0.07 0.15 0.19 0.27 0.44 0.51 0.63 0.68 0.83 0.88 0.93 0.93 0.98 1 1

0.07 0.15 0.19 0.25 0.37 0.38 0.43 0.42 0.42 0.36 0.26 0.10 0.05 0.04 0.02

0.59 0.61 0.62 0.64 0.68 0.70 0.74 0.75 0.82 0.84 0.86 0.75 0.80 1 1

1 1 1 0.92 0.82 0.75 0.70 0.67 0.61 0.56 0.51 0.46 0.44 0.44 0.44

Sens = sensitivity, Spec = specificity, PPV = positive predictive value, NPV = negative predictive value. Out = outpatient psychotherapy patients; In = inpatient psychiatric patients.

tion of the scales for ‘anti-social’ (r = 0.18, p < 0.10) and ‘histrionic’ (r = 0.13, not significant (n.s.)). The clinical differentiation ability of the PSS-K total score is given, since the sample from the general population differs from all the other samples (table 1; F(4.620) = 49.13, p < 0.001). As expected, the lowest PSS-K total score was found for the subjects from the general population, and the highest for the psychiatric patients. Determination of a Cut-Off Value The cut-off value is determined by Receiver Operating Characteristic (ROC) analysis [Murphy et al., 1987]. The area under the ROC curve, as a global measure of the quality of the test, is 0.79 (95% confidence interval: 0.70–0.88). Table 4 shows possible cut-off values and diagnostic parameters. The following abbreviations are used to represent the qual-

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Dis

ity criteria and their calculations: true-positive (RP), falsepositive (FP), true-negative (RN), and false-negative (FN). The sensitivity is a measure of the hit rate – i.e., the probability that a sick person will be so recognized by a test (RP/(FP + FN)). The specificity is the proportion of correct rejections (RN/(FP + RN)). The positive predictive value (PPV) is the probability that a positive test result means there is actually an illness (RP/(RP + FP)). The negative predictive value (NPV) denotes the probability that a negative test result means there is no illness (RN/(RN + FN)). The Youden Index is derived from sensitivity + specificity −1, and indicates the threshold value for which the sum of sensitivity and specificity is greatest and therefore the separation of the groups is best [Moosbrugger and Kelava, 2007]. The definition of a suitable separation value requires consideration of various criteria, which will be taken up in the discussion.


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Discussion The aim of this study was to develop a short and valid screening questionnaire, which should indicate the presence of a PD in the two-step diagnostic process. The first question is whether the reliability of the PSS-K, estimated on the basis of the internal consistency of Cronbach’s _ of 0.69, is appropriate. The following points should be considered: Moosbrugger and Kelava [2007] note that the reliability of screening methods is usually low, due to the low number of items compared to more detailed procedures, and the reliability of an individual scale of common personality tests is often only in the range of 0.70 [Kelava and Moosbrugger, 2007]. An extension of the PSS-K from 8 items to 16 would increase the reliability to _ = 0.82 [Moosbrugger and Kelava, 2007]. In addition, PDs are very heterogeneous constructs and are therefore best assessed by instruments with heterogeneous items. In the PSS-K, this is done by a rather small item inter-correlation at the level of r_ = 0.21. Moosbrugger and Kelava [2007] point out in this regard that the reliability is greatly underestimated when there is low consistency, under circumstances in which the heterogeneous items do indeed lower the reliability as determined by consistency analysis, but may still achieve a high predictive validity. Furthermore, comparable short screening instruments such as the SAPAS show a similarly small reliability, with Cronbach’s _ = 0.68 [Moran et al., 2003]. Against this background, the reliability of the PSS-K can be regarded as sufficient. For future studies, the retest reliability of the PSS-K should be used as an additional measurement.The validation by the gold standard (SCID-II) is very promising. The total score of the screening and the individual items correlate significantly with the number of PDs and mainly with the dimensional QSs of the SCID-II. The PSS-K total score predicts the existence of at least one PD already validated by the SCID-II. It was possible to prove the clinical differentiation ability of the PSS-K. The subsamples differ significantly in their PSS-K total score.

When determining an appropriate cut-off value, the following points should be considered: If the screening is to be used as a first diagnostic step for rapid detection of a specific illness, and, in the event of a positive result, a detailed diagnosis for the specification of the disease is to be performed as the second step, then the main goal is to detect all those who have an illness. This requires the highest possible sensitivity, combined with acceptable specificity. Following this criterion, we would opt for the threshold value of >4 (sensitivity = 0.93, specificity = 0.44). The probability that a positive result of the PSS-K is correct at this cut-off value is 68% (PPW); a negative screening result is correct in 82% of cases (NPV). However, if we want to focus on the choice of a suitable cut-off value on the Youden Index, we would argue for the separation value of >6. A sensitivity of 0.80 will recognize 80% of those with an illness, but a PD will be overlooked in 20% of cases. The PPV is 0.74 and the NPV is 0.70. For use of the PSS-K in the two-stage diagnostic process, the choice of a suitable cut-off value does not put the emphasis on balancing of sensitivity and specificity (maximal Youden Index), but rather on the highest possible sensitivity (high hit rate), with sufficient specificity (not too many false-positive diagnoses). The cut-off value >4 should be chosen for additional weighting of the consequences of a false-negative diagnosis (a ‘miss’ – overlooking an existing PD) compared to the consequence of a falsepositive diagnosis (a ‘false alarm’ – requiring additional testing). Looking at comparable parameters of the IIP-PD, which is so far the only English screening questionnaire (28 items; sensitivity = 0.91, specificity = 0.40) [Pilkonis et al., 1996], the screening parameters used in the PSS-K are very positive. In future studies validating the PSS-K, the suitability of this separation value should be tested using different samples.

Disclosure Statement The authors declare that they have no conflict of interest.

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