Validity and reliability of the Danish version of QUALIDEM.

INTRODUCTION: QUALIDEM is a dementia-specific QoL instrument that allows a proxy-based Quality of Life rating in all stages of dementia. It was originally developed in The Netherlands and has later been translated into English and German. This study endeavoured to translate, cross-culturally adapt and test important psychometric properties of a Danish version in a cross-sectional validation study with a nested test-retest design. METHOD: All items underwent forward and backward translation by bilingual academics. Persons with dementia were recruited from 28 healthcare units in a Danish municipality. The severity of dementia was determined using a pragmatic approach allowing the site team to trichotomise the disease (mild, moderate-severe and very severe) before scoring the QUALIDEM. Psychometric properties for QUALIDEM were determined for item characteristics, construct validity, internal consistency, test-retest reliability, measurement error and floor and ceiling effects. The study was approved by The Danish Data Protection Agency. RESULTS: A total of 169 persons with dementia, aged 51-103, were included. The construct validity testing showed that the overall proportion of correctly hypothesised correlations was 83%. Testing for internal consistency, Cronbach's α ranged from 0.65 to 0.85 in mild-severe dementia with three out of nine subscales having values below 0.7. For very severe dementia, Cronbach's α ranged from 0.44 to 0.81, with three out of six subscales having insufficient values. For test-retest reliability, the intra-class correlation coefficients ranged from 0.56 to 0.86. The 'scale width' method revealed a marked ceiling effect in all subscales ranging from 30.6% to 87.7%. DISCUSSION: The QUALIDEM was successfully translated and cross-culturally adapted into Danish. Most subscales show acceptable internal consistency and test-retest reliability. However, a substantial measurement error and ceiling effect was present in most subscales. CONCLUSION: With few exceptions, the subscales of the Danish version of QUALIDEM have acceptable validity and reliability. Future research should address the limitations of the ceiling effects.