Cross-Cultural Validation of the COmprehensive Score for Financial Toxicity (COST) Measure in an Australian Sample

The COmprehensive Score for Financial Toxicity (COST) measure developed in the United States measures the financial impact resulting from cancer and its treatment. This paper reports on an Australian cross-cultural validation of the COST measure.

Participant eligibility criteria included individuals aged ≥ 18, undergoing or completed primary treatment for cancer. Immediate family members of patients were also eligible for Phase 1. Face and content validity were assessed through concurrent interviews and a brief survey (Phase 1). The subsequent revised version of COST was field-tested using a prospective sample of participants to examine item importance, internal consistency reliability, and construct validity (Phase 2).

Phase 1: Pretesting included 20 patients and two family members (mean age 61, range: 20-87). 19 or more patients agreed or strongly agreed that the COST items were written in clear language, easy to understand, and relevant to their experiences. Content analysis of interviews led to the inclusion of two family-related items to improve content coverage (hereby referred to as Australian-COST), along with two additional stand-alone items to facilitate clinical actions. Phase 2: One hundred and twenty-two patients completed a field-test survey. Each Australian-COST item was rated as "extremely important" or "important" by most participants (62%-81%). Cronbach's alpha coefficients were > 0.9 for both the COST and the Australian-COST. Exploratory factor analysis revealed two factors, explaining 64% (COST) and 63% (Australian-COST) of the variance. Both measures discriminated between low and high household income groups (< $39,999/year, > $125,000/year), demonstrating known-groups validity (COST: mean 19.51 vs. 28.33, p = 0.002, Australian-COST: mean 23.51 vs. 33.29, p = 0.006).

The COST is a valid and reliable measure for Australian cancer patients, and the results largely support the construct equivalence across the United States and Australia. The revised version contains new family-related items to enhance content coverage, which may be applicable in other countries where the financial impact of cancer on the family is of significant concern for patients.