Swedish universities scales of personality : relationship to other personality instruments, patient-control differences and longitudinal stability in schizophrenia and related disorders

Abstract

Objective: Schizophrenia and related disorders are often severe and chronic. They could also cause a lasting change in the life situation of the affected individual. Personality is an aspect that can affect symptoms and social function in schizophrenia spectrum disorder. The first aim of the thesis was to evaluate the use of the Swedish universities Scales of Personality (SSP) with regard to factor structure, internal consistency and case-control differences. The second aim was to investigate stability over five- and 13-year periods among patients with schizophrenia and related disorders and healthy individuals. The third aim was to investigate associations between SSP and scales from four other personality instruments among healthy subjects. A fourth aim was to investigate differences between patients with long-time treated psychotic disorder and control related to personality traits.

Method: Patients and controls were recruited as part of the larger Human Brain Informatics (HUBIN) study at Karolinska Hospital and Institutet in Stockholm, Sweden. In order to investigate aspects of usability and differences between patients and controls using SSP, factor structure and internal consistency in patients with psychotic disorder and healthy controls were analysed by multiple analysis of covariance (MANCOVA) and Cronbach’s alpha. Stability of personality traits were investigated during a five-year follow up study and also during a 13-year period in a second follow up study. Patients with schizophrenia and related disorders and healthy controls completed SSP upon two or three occasions at baseline, after five years and after 13 years. The three factors and 13 scales of SSP were analysed for effect of time and case-control differences. MANCOVA, correlations, means and SD’s were calculated. To investigate SSP in relation to other personality constructs the healthy controls completed SSP and at least one of the personality instruments NEO-PI-R, revised Chapman scales, SCID-II screen or STQ. Correlations were calculated between SSP´s three factors as well as between the 13 different SSP scales and scales/subscales in revised Chapman scales, NEOPI- R, SCID-II screen and STQ. Factor analyses and ICC were calculated.

Results: When measuring differences and aspects of usability with SSP internal consistencies were overall similar comparing patients and controls. The patients scored significant lower in three (Adventure Seeking, Physical Trait Aggression, Verbal Trait Aggression) and higher in seven (Detachment, Embitterment, Lack of Assertiveness, Mistrust, Psychic Trait Anxiety, Somatic Trait Anxiety, Stress Susceptibility) in the SSP inventory scales. There was no significant difference between controls and patients in the scales Impulsiveness, Social Desirability, and Trait Irritability scales. SSP factor analyses among patients with schizophrenia spectrum disorder showed a three-factor model, as anticipated. Factor Neuroticism was similar to the Swedish normative study. Factor Aggressiveness also included high loadings from the scales Adventure Seeking, Impulsiveness and Mistrust, both scales which in the Swedish normative study loaded in third factor Extraversion (Adventure Seeking and Impulsiveness) and factor Neuroticism (Mistrust). Factor Extraversion consisted of the scales Detachment and Social Desirability scales. For Detachment that is as in the Swedish normative study. Social Desirability loaded on the Aggressiveness factor in the Swedish normative study. At five-year follow up MANCOVA within-subjects analysis did not show any effect of time. Patients scored higher than controls in seven of the SSP scales, i.e. Detachment, Embitterment, Mistrust, Lack of Assertiveness, Psychic Trait Anxiety, Somatic Trait Anxiety and Stress Susceptibility. At 13-year follow up tests of within-subject correlations showed differences in the two scales Lack of Assertiveness and Physical Trait Aggression. Lack of Assertiveness were influenced by age and in Physical Trait Aggression the controls rated themselves less aggressive at higher age whereas the patients’ ratings were stable. Between-subjects correlations showed differences in the factor Neuroticism and also in nine of the 13 scales of SSP. When investigate SSP scales and factors in relation to scales in other personality instruments weaker correlations were common and strong correlations were sparse. SSP Aggressiveness factor correlated with NEO Agreeableness (r=0.62). SSP Extraversion factor correlated with NEO Extraversion (r=0.63) and SSP Neuroticism factor correlated with Chapman Social anhedonia (r=0.62), NEO Neuroticism (r=0.80) and SCID-II cluster C (r=0.71).

Conclusion: The personality inventory SSP can be used assessing personality traits in patients with schizophrenia and related disorders in stable remission. SSP is particularly useful when measuring personality traits related to temperament-like features. The different personality inventories measure personality aspects in partly different ways and are therefore not completely comparable to each other. SSP personality traits showed relatively high stability among patients with schizophrenia and related disorders. Healthy controls showed a higher stability than the patients.