Evaluation of Qualidem: a dementia-specific quality of life instrument for persons with dementia in residential settings; scalability and reliability of subscales in four Dutch field surveys.

OBJECTIVE: To evaluate the scalability and reliability of Qualidem, a quality of life observation instrument rated by professional caregivers of persons with mild to very severe dementia living in residential settings.
METHOD: Data from four field surveys in the Netherlands were used. The instrument consists of nine subscales for mild to severe dementia; of which six can be applied in very severe dementia. The Mokken scaling model was used to compute scalability and reliability coefficients for each subscale and dementia group.
RESULTS: Seven hundred fifty nine persons with mild to severe dementia and 214 persons with very severe dementia residing in 36 nursing homes and 4 homes for the elderly were included. In general, the subscales for the mild to severely demented group were scalable and (moderate) sufficiently reliable; the results confirmed the results of previous research to develop Qualidem. For the very severe demented group, four out of six subscales were scalable (Care relationship, H = 0.56; Positive affect, H = 0.55; Restless tense behavior, H = 0.42; and Social isolation, H = 0.34); they were also sufficiently reliable to measure quality of life (0.57 ≤ ρ ≤ 0.82). From the other two measured subscales, Social relations was considered not scalable (H = 0.26) and Negative affect was scalable (H = 0.36), but insufficiently reliable (ρ = 0.40).
CONCLUSION: Qualidem is an easy to administer and overall moderately sufficient reliable rating scale that provides a quality of life profile of persons with mild to even very severe dementia living in residential settings.