Validation of the German version of the Subjective Scale to Investigate Cognition in Schizophrenia (SSTICS)

Schizophrenia Spectrum Disorders (SSD) are characterized by cognitive deficits that can significantly impact daily functioning and quality of life. The Subjective Scale to Investigate Cognition in Schizophrenia (SSTICS) is a widely used self-report tool for assessing subjective cognitive impairments. This study validates the German version of the SSTICS. Data from N = 308 participants (38% female) with SSD were analyzed to evaluate factor structure, reliability, and convergent/discriminant validity. A second sample of N = 60 inpatients (37% female) with SSD was used to assess sensitivity to change over a four-week treatment period. The SSTICS and its 14-item short form demonstrated high internal consistency (Cronbach's α = 0.90 and 0.88, respectively) and reliability (McDonald's ω hierarchical = 0.900 and 0.881, respectively). Confirmatory factor analysis supported a five-factor model (memory, attention, executive functions, language, and praxia): Comparative Fit Index (CFI) = 0.97, Root Mean Square Error of Approximation (RMSEA) = 0.08. Strong correlations with the Cognitive Fusion Questionnaire (r = 0.60) and the cognitive domain of the WHO Disability Assessment Schedule 2.0 (r = 0.73) supported convergent validity. Low correlations with the cognitive factors of the Positive and Negative Syndrome Scale (r ≤ 0.29) suggest a discrepancy between subjective and clinician-rated cognitive impairments. The SSTICS showed sensitivity to change: minimal detectable change (MDC) = 0.54, though responsiveness was limited: responsiveness ratio (RR) = -0.435. Overall, the German SSTICS is a reliable and valid instrument for assessing subjective cognitive impairments in SSD. The study underscores the relevance of self-reported cognitive difficulties in clinical contexts. Future research should explore associations with objective neurocognitive measures and long-term sensitivity to change.