Scale Development with Factor Analysis: A Robust Method for Patient-Reported Outcome Measurement in Gallstone Surgery Research (Motivated by the Development of the Gothenburg Gallstone Questionnaires by Pålsson et al.)

The development of psychometrically sound instruments is critical for accurately capturing patient-reported outcomes, particularly in complex surgical contexts where quality-of-life dimensions are multidimensional and subjective. This report illustrates the application of scale development with factor analysis using the Gothenburg Gallstone Questionnaire as a motivating example. Through an iterative process involving item generation, pilot testing, and exploratory factor analysis, the research team developed two reliable and interpretable self-report instruments tailored to gallstone surgery patients' preoperative and postoperative experiences. The methodology enabled the identification of coherent domains—such as pain, gastrointestinal symptoms, emotional well-being, and physical functioning—while minimizing redundancy and measurement bias. Key outputs included inter-item correlation matrices, scree plots, factor loading tables, and reliability coefficients, all of which supported the final scales' internal consistency and structural validity. The use of moderate sample sizes, diverse patient experiences, and a transparent analytic process underscores the rigor of the development strategy. While limitations such as reliance on measured constructs and subjective model decisions persist, the study highlights the potential of factor analysis to enhance outcome measurement. Future directions include integrating modern psychometric tools and validating instruments across broader populations. This approach supports more robust, patient-centered evaluation in clinical research and practice.