Supplementary file 1_Development and validation of the Sensitivity to Intrusiveness Questionnaire.docx

IntroductionIntrusive thoughts are involuntary mental experiences associated with various psychopathologies and can be disruptive. Although most research on intrusive thoughts focuses on negative content, intrusive thoughts are not defined solely by what they contain. Recent findings suggest that the distress associated with intrusive thoughts is driven more by individual characteristics than by the content of the thoughts themselves. To capture such content-independent individual differences, the present research focuses on the development and validation of the Sensitivity to Intrusiveness Questionnaire (STIQ).
MethodsAcross four studies conducted in different countries (N = 615), the psychometric properties of the STIQ were examined. Analyses assessed factor structure, internal consistency, test–retest reliability, and associations with personality traits and clinical groups.
ResultsResults supported a stable three-factor structure of the STIQ, reflecting negative experience of thoughts, awareness and monitoring of thoughts, and perceived lack of control over thoughts. The questionnaire demonstrated high internal consistency and test–retest reliability and showed meaningful variance across personality traits and clinical groups, independent of intrusive thought content.
DiscussionThe findings highlight the utility of the STIQ in capturing a transdiagnostic, content-independent sensitivity to intrusiveness. The STIQ provides a novel tool for examining individual differences and the mechanisms underlying distress associated with intrusive cognitions, contributing to a more comprehensive understanding of intrusiveness in psychological phenomena.