Item distribution, internal consistency and inter-rater reliability of the German version of the QUALIDEM for people with mild to severe and very severe dementia

BACKGROUND The QUALIDEM is a dementia-specific Quality of life (Qol) instrument that is recommended for longitudinal studies and advanced stages of dementia. Our study aimed to develop a user guide for the German version of the QUALIDEM and to determine the item distribution, internal consistency and inter-rater reliability (IRR) of the German QUALIDEM. METHODS A user guide was developed based on cognitive interviews with ten professional caregivers and a focus group with six professional caregivers. The item distribution, internal consistency and IRR were evaluated through a field test including n = 55 (mild to severe dementia) and n = 36 (very severe dementia) residents from nine nursing homes. Individuals with dementia were assessed four times by blinded proxy raters. RESULTS A user guide with instructions for the application of the QUALIDEM and definitions and examples for each item was created. Based on the single-measure intra-class correlation coefficient (ICC for absolute agreement), we observed strong IRR for nearly all of the QUALIDEM subscales, with ICCs of at least 0.79. A lower ICC (ICC = 0.64) was only obtained for people with very severe dementia on the 'negative affect' subscale. CONCLUSIONS The IRR improved based on the application of the QUALIDEM user guide developed in this study. We demonstrated a sufficient IRR for all subscales of the German version of the QUALIDEM, with the exception of the 'negative affect' subscale in the subsample of people with very severe dementia. The item distribution and internal consistency results highlight the need to develop new informative items for some subscales.