New evidence for content validity of the German version of the Acute Cystitis Symptom Score: cognitive interview study among patients and experts.

Objective: The Acute Cystitis Symptom Score (ACSS) is a clinically validated instrument to assess symptoms and quality of life in women with uncomplicated urinary tract infections (uUTIs). A previous study examining the content validity of the German version of the ACSS has shown some methodological limitations when rated against the criteria for content validity of the COnsensus-based Standards for the Selection of Health Measurement INstruments (COSMIN) initiative. Extending the existing evidence, the present study aimed to assess the content validity of the German version of the ACSS according to the criteria of the COSMIN methodology.

Methods: In individual cognitive interviews following a structured, standardized interview guide, women with a history of uUTI and experts from different medical fields rated the instructions, items, response options and recall period of the ACSS in terms of relevance, comprehensiveness and comprehensibility. Additionally, the Content Validity Index (CVI) was calculated based on expert assessments to quantify content validity.

Results: A total of 14 patients and 14 experts participated in two rounds of interviews. The overall relevance and comprehensiveness of the instrument were rated as appropriate. Modifications focused on improving comprehensibility. Ten items underwent minor modifications or were given examples to enhance comprehensibility. The scales of five items were linguistically revised. Confirming good content validity, CVI was 0.97.

Conclusions: Comprehensive qualitative assessments support content validity of the ACSS for evaluating symptoms and quality of life in women with uUTIs. Minor modifications addressed comprehensibility. Psychometric validation of the revised ACSS is recommended.