Psychometric analysis of the brief symptom inventory 18 (BSI-18) in a representative German sample

Background: The BSI-18 contains the three six-item scales somatization, depression, and anxiety as well as the Global Severity Index (GSI), including all 18 items. The BSI-18 is the latest and shortest of the multidimensional versions of the Symptom-Checklist 90-R, but its psychometric properties have not been sufficiently clarified yet. Methods: Based on a representative sample of N = 2516 participants (aged 14-94 years), detailed psychometric analyses were carried out. Results: The internal consistency was good: Somatization alpha=.82, Depression alpha=.87, Anxiety alpha=.84 and GSI alpha=.93. Confirmatory factor analysis supported the three scales as second-order and GSI as first-order factors. The model fit based on RMSEA is good but that model fit based on CFI and TLI are too low. Conclusions: Therefore, it is a very short, reliable instrument for the assessment of psychological distress. The BSI-18 can be used to reliably assess psychological distress in the general population. However, further studies need to evaluate the usefulness of standardization in clinical samples.