SCQOLIT-SF: A revised outcome measure for assessing patient-reported outcomes in non-melanoma skin cancers.

Basal and squamous cell carcinomas (BCCs and SCCs, respectively) pose significant burden for patients and health services. Measuring the quality of life in this cohort is crucial because the management of these cancers may cause significant morbidity despite the low overall mortality. The Skin Cancer Quality Of Life Impact Tool (SCQOLIT), a 10-item patient-reported outcome measure, is widely used for quality-of-life assessment but it has not been validated using factor analysis or Rasch Measurement Theory (RMT). Using these contemporary psychometric techniques, we assessed the validity of SCQOLIT for evaluating quality of life in non-melanoma skin cancer. Following the evidence from an expert Patient Public Involvement group, we created the SCQOLIT-SF by removing two SCQOLIT items that were less relevant to this cohort, and explored its validity. Patients with BCC/SCC completed SCQOLIT preoperatively and three months post-operatively. Patients with high-risk SCCs also completed SCQOLIT at 6-9 months. Overall, 572 questionnaires responses, completed by 279 patients, were included in the final analysis. Exploratory and confirmatory factor analyses indicated a single factor underpinning SCQOLIT and SCQOLIT-SF. RMT revealed close and disordered item response thresholds and elements of local dependency in both questionnaires. These were largely resolved through rescoring of item responses. However, we also identified a significant negative skew across all item responses in both questionnaires, indicating that they were intended for patients with more significant disease burden than those in our cohort. Finally, we showed that the assessment of both questionnaires can be improved through conversion of raw questionnaire scores to continuous Rasch scoring.