Adaptation of the PROFFIT Instrument Into Turkish: A Validity and Reliability Study

Primary outcomes

1. Validity Assessment-Language and Content Validity

   Time frame: Through study completion, an average of 12 months

   Language and Content Validity: To assess the relevance and appropriateness of the translated items, a panel of at least six experts in oncology, psychology, and instrument development will evaluate each item.

2. Validity Assessment-Content Validity Index (CVI)

   Time frame: Through study completion, an average of 12 months

   Content Validity Index (CVI) will be calculated based on expert ratings to determine the proportion of items deemed relevant.

3. Validity Assessment-Content Validity Ratio (CVR)

   Time frame: Through study completion, an average of 12 months

   Content Validity Ratio (CVR) will be used to assess whether each item is essential for measuring the construct.

4. Validity Assessment-Construct Validity

   Time frame: Through study completion, an average of 12 months

   Confirmatory Factor Analysis (CFA) will be performed to verify whether the factor structure of the Turkish version aligns with that of the original instrument.

   Model fit indices such as χ²/df, RMSEA, CFI, TLI, and SRMR will be used to evaluate the adequacy of the factor structure.

5. Validity Assessment- Criterion Validity

   Time frame: Through study completion, an average of 12 months

   The Turkish PROFFIT scores will be correlated with other established patient-reported outcome measures, specifically the COST (v2) and EORTC QLQ-C30 instruments, to assess convergent validity.

   Pearson or Spearman correlation coefficients will be used to determine the strength of associations between PROFFIT and these validated measures.

6. Validity Assessment- Known-Group Validity

   Time frame: Through study completion, an average of 12 months

   To assess whether the instrument can differentiate between groups with known differences in financial toxicity, mean scores of the total and subscales will be compared across predefined demographic and clinical groups.

   Independent samples t-tests and ANOVA will be performed to compare group differences.

7. Reliability Assessment

   Time frame: Through study completion, an average of 12 months

   Internal Consistency: The reliability of the Turkish PROFFIT instrument will be evaluated using:

   Cronbach's alpha (α) to assess the overall internal consistency of the scale. McDonald's omega (ω) as an alternative measure that provides a more robust estimation of reliability in multidimensional scales.