Ensuring reliability and cultural validity of the Indonesian version of the Quality Of Life Index for patients with cancer

The objective of this study was to translate the Ferrans and Powers Quality of Life Index (QLI) into the Indonesian language, considering its cultural and functional appropriateness, and to evaluate its psychometric properties by testing the reliability and validity. A committee approach was conducted to create the Indonesian version of the QLI (QLI-Id) and cognitive interviewing with 15 patients with cancer was conducted to identify potential problems or errors in answering the QLI-Id. A cross-sectional descriptive study was carried out using 236 responses to the QLI-Id questionnaire from patients with cancer; 62 of whom completed the same questionnaire twice within a 3-week interval to verify stability reliability. Confirmatory factor analysis results supported construct validity with model fit statistics for the original single-factor and four-factor structure of the QLI (corresponding to the QLI's total score and four subscale scores, respectively) with some rearrangement of the items within each subscale. Reliability for the total QLI-Id scale was supported by McDonald's Omega of 0.92 and the intraclass/intrasubject correlation coefficient at two time points of 0.86. The strong correlation between the QLI-Id total and the Satisfaction with Life Scale scores and the overall health/QOL domain of the EORTC QLQ-C30 (both r = 0.73) supported its construct validity. This study provides evidence for the reliability and validity of the QLI-Id as an instrument to measure the impact of cancer on the overall QOL of Indonesian patients.