The Psychometric Properties of the Personality Assessment Inventory (PAI) Somatic Complaints (SOM) Scale

Somatization is exemplified by an individual experiencing and reporting a wide range of non-specific physical symptoms, which may or may not be associated with a known physical etiology. The Personality Assessment Inventory (PAI) is frequently administered in clinical contexts and has utility in evaluating models of psychopathology, which include somatization. This research examines the psychometric properties of the PAI Somatic Complaints (SOM) scale in an outpatient mental health clinical sample (N=361). A confirmatory factor analysis (CFA) was conducted to determine the factor structure of the PAI SOM scale. Item response theory (IRT) was then utilized to examine item level functioning of the scale. A bifactor SOM model exhibited excellent fit and consisted of a general Somatic Complaints factor and subfactors reflecting Health Concerns, Conversion, and Somatization subscales. The bifactor graded item response model analyses illustrate SOM items with high discrimination and moderate difficulty reflect general health status and adequately quantify somatic symptom reporting. SOM items with high or low difficulty and low discrimination tended to reflect unusual somatic symptoms. A bifactor SOM model exhibited excellent fit and consisted of a general Somatic Complaints factor and subfactors reflecting Health Concerns, Conversion, and Somatization subscales. The bifactor graded item response model analyses illustrate SOM items with high discrimination and moderate difficulty reflect general health status and adequately quantify somatic symptom reporting. SOM items with high or low difficulty and low discrimination tended to reflect unusual somatic symptoms. Overall, SOM has relatively strong psychometric properties and most efficiently quantifies somatic symptom reporting between T scores of 55 and 70, which largely reflects mild to moderate symptoms. Increased understanding of how the scale functions allows clinicians to utilize SOM to detect somatic symptom reporting effectively and efficiently in their patients.