[Development and validation of the Subclinical Stress Symptom Questionnaire SSQ-25]

Stress symptoms are widespread in the general population and often occur in the early course of mental disorders. However, no validated instrument was available for the study of subclinical stress symptoms and their relevance in the study of psychopathological trajectories. In order to advance and systematize the study of the etiology and pathogenesis of diseases in subclinical populations, the Subclinical Stress Symptom Questionnaire (SSQ-25) was developed in the present study.

In the course of three online studies, a total of 1174 subjects were recruited. The first study included item selection and the development of the questionnaire based on the analysis of item parameters, reliability, and exploratory factor analysis. To validate the factor structure, confirmatory factor analysis was used. Validation analyses were applied to distinguish the SSQ-25 from three clinical measures: Beck's Anxiety and Depression Inventory (BAI and BDI), and the Posttraumatic Stress Diagnostic Scale (PDS). In the third study the subclinical property of the instrument was investigated.

Exploratory and confirmatory factor analyses revealed and confirmed a two-factor model (psychological and physiological stress symptoms). Cronbach's alpha was 0.95. The subclinical property of the SSQ-25 was confirmed by means of item information functions, scatter plots, residuals, and Koenker-Bassett tests as opposed to established clinical measures.

The SSQ-25 is a comprehensive, reliable, and valid instrument that allows a valid assessment and differentiation of subclinical stress symptoms.