Development and validation of the Japanese version of the Death Literacy Index (DLI-J) and its short form (DLI-J-9)

To translate, culturally adapt, and psychometrically validate the Japanese version of the Death Literacy Index (DLI-J) and its short-form version (DLI-J-9) to assess death literacy among Japanese adults.

A multiphase mixed-methods design was employed. The process included forward translation, reconciled single translation, back translation, translation review, cognitive interviews (n = 8), and psychometric validation using a nationally representative online sample of 2500 Japanese adults aged 20-79 years. Participants completed an online survey, with a subsample (n = 300) completing a retest after 4 weeks. Confirmatory factor analysis (CFA), internal consistency, construct validity, and test-retest reliability were evaluated.

The DLI-J demonstrated excellent psychometric properties. CFA supported the six-factor structure of the DLI-J (Tucker-Lewis index [TLI] = 0.940, comparative fit index [CFI] = 0.947, standardized root mean square residual [SRMR] = 0.048, and root mean square error of approximation [RMSEA] = 0.063) and the two-factor structure of the DLI-J-9 (TLI = 0.945, CFI = 0.960, SRMR = 0.042, and RMSEA = 0.069). Internal consistency was excellent for the total DLI-J scale (α = 0.959) and all subscales (α = 0.870-0.959). Convergent validity was supported by positive correlations with death competency, whereas discriminant validity was confirmed by negligible correlations with loneliness. Known-groups validity was established, with higher scores among bereaved individuals and end-of-life care professionals. The test-retest reliability was moderate to good (intraclass correlation coefficient [ICC] = 0.515-0.819). The overall DLI-J mean score was 3.82 (standard deviation = 1.91), lower than international benchmarks. Floor effects were observed in the hands-on care, accessing help, and community support subscales.

The DLI-J and DLI-J-9 are psychometrically robust instruments for assessing death literacy.