Toward a validated European instrument to measure the socioeconomic impact of cancer.

A cancer diagnosis can impose a financial burden on patients and their families, defined as socio-economic impact (SEI) within a framework of the Organization of European Cancer Institutes (OECI). The Socio-Economic Consequences of Cancer (SEC) study assessed SEI in 25 European countries using the Canadian Financial Index of Toxicity (FIT) instrument, showing substantial variation and supporting the need for a validated Europe-specific instrument. We examined the FIT instrument's validity and reliability in a secondary analysis of the SEC study, exploring whether the SEI framework supported its validation. Factor analyses were performed on the largest subgroup sharing cancer type, language, and country. The aim was to test whether the Canadian model could be replicated or a SEI-based model fit better. Reliability and construct validity were analyzed, followed by configural invariance and Differential Item Functioning (DIF) analysis for cross-country comparability. We used data from Bulgaria, France, Germany, the Netherlands, Norway, and Spain. The original FIT-instrument failed to replicate in the Spanish sample, leading to an SEI-based model with better fit (CFI = 0.975, RMSEA (90% CI) = 0.104 (0-0.278), χ2 = 18, p = .60). The instrument was reliable. Construct validity was partly confirmed. Configural invariance testing suggested that the SEI-based model's factor structure fits better in Europe, while DIF was identified, implying that direct score comparisons across countries should be done with care. In conclusion, the original FIT-instrument could not be fully validated in Europe whereas the SEI-framework improved score interpretation, supporting its use in developing a validated instrument tailored to the European context.