Reliability and validity of the Japanese version of the Quality of Life Index for patients with cancer

This study was designed to evaluate the psychometric properties of the newly completed Japanese translation of the Ferrans and Powers Quality of Life Index Cancer Version III (QLI). Using a cross‐sectional descriptive design, 136 ambulatory patients with gastrointestinal cancer (55 receiving chemotherapy, 76 with stable health status after treatment, and five status not known) completed a questionnaire at a one‐time point, and 26 patients (stable health status) completed the questionnaire again 2 weeks later. Internal consistency reliability was supported by Cronbach's α of .96 for the total scale, with subscales ranging from .83 to .93. A test–retest correlation of 0.76 (total scale) provided evidence of stability reliability over a 2‐week period, with subscale retest correlations ranging from 0.70 to 0.83. Confirmatory factor analysis showed the same four domains for the Japanese translation as the original QLI, supporting construct validity. We also assessed construct validity by examining the relationships between the Japanese QLI and six other concepts known to be related to the quality of life. As hypothesized, all correlations were moderate and in the expected direction (pain −0.39, anxiety −0.54, depression −0.63, stress −0.51, pain interfering with functioning −0.52, and general health 0.62). This evidence of the reliability and validity of the Japanese translation of the QLI supports its use in research and clinical practice to evaluate the impact of cancer and treatment. This new translation can be used to assess the patient's perspective of their quality of life, both within Japan and in cross‐cultural studies with the QLI in other languages.