Content validity for dementia of three generic preference based health related quality of life instruments.

A semi-structured interview was conducted with dementia patients and their caregivers in order to explore which aspects of quality of life were perceived as relevant and important. These aspects of quality of life were compared with the content of three generic utility-based quality of life instruments: European Quality of Life Instrument, Health Utilities Index, and Quality of Well-Being (QWB) Scale. Twenty patients with mild dementia and 20 caregiver volunteers provided narrative data derived from interviews that were analyzed using a modified Grounded Theory method of analysis. Essential attributes of dementia quality of life identified by the respondents were missing in the three utility-based quality of life instruments selected for the study. Patients provided a wider range of attributes than the instruments including some attributes not described by caregivers. Of the three utility-based measures, the QWB scale included the largest number of quality of life attributes but still missed many. Compared to the respondent generated attributes all three utility-based quality of life instruments have important shortcomings in content validity.