Abstract
BackgroundThe Quality of Life in Alzheimer’s disease scale (QoL-AD) is a widely used Health Related Quality of Life (HRQoL) instrument. However, studies investigating the instrument’s inter-rater reliability (IRR) are missing. This study aimed to determine the item distribution and IRR of the German proxy version of the QoL-AD (13 Items) and a nursing home-specific instrument version (QoL-AD NH, 15 Items).MethodsThe instruments were applied to 73 people with dementia living in eight nursing homes in Germany. Individuals with dementia were assessed two times by blinded proxy raters. The IRR analyses were based on methodological criteria of the quality appraisal tool for studies of diagnostic reliability (QAREL), the COSMIN group and the single-measure Intra-Class Correlation Coefficient (ICC) for absolute agreement ≥0.70.ResultsAll items for both instrument versions demonstrated acceptable item difficulty, with the exception of one item (QoL-AD proxy). The IRR was moderate for the QoL-AD (ICC: 0.65) and insufficient for the QoL-AD NH (ICC: 0.18). The additional computation of the average measure ICC for two proxy-raters demonstrated a strong IRR (ICC: 0.79) for the QoL-AD and a weak IRR for the QoL-AD NH (ICC: 0.31). The detailed analysis of the IRR for each item underpinned the need for the further development of both instruments.ConclusionsThe unsatisfactory IRRs for both instruments highlight the need for the development of a user guide including general instructions for instrument application as well as definitions and examples reflecting item meaning. Priority should be given to the development of reliable proxy-person versions of both instruments.Trial registrationClinicalTrials.gov: NCT02295462, Date of registration: 11–20-2014.
Highlights
The Quality of Life in Alzheimer’s disease scale (QoL-AD) is a widely used Health Related Quality of Life (HRQoL) instrument
A varying understanding of this criterion by the assigning head nurse may be jointly responsible for the inter-rater reliability (IRR) results. This IRR study demonstrated a moderate IRR for the QoL-AD based on a proxy-proxy perspective and an insufficient IRR for the QoL-AD NH
We recommend the development of a user guide including general instructions for the application of both instruments as well as definitions and examples reflecting the meaning of each item
Summary
The Quality of Life in Alzheimer’s disease scale (QoL-AD) is a widely used Health Related Quality of Life (HRQoL) instrument. According to Pickard & Knight [12] the proxy-rating perspectives “proxy-proxy” and “proxy-person” have been distinguished While in the former perspective the proxy rates the HRQoL of a person with dementia from his/her proxy perspective, in the latter perspective a proxy assesses the QoL of a person with dementia as he/she thinks the person with dementia would rate him or herself [12]. One recent study investigated both perspectives (proxy-proxy and proxy-person), comparing them to self-reports of people with and without dementia in nursing homes. The tendency to attenuate self-ratings existed for both proxy-perspectives with a smaller perspective gap between self-ratings and the proxy-person perspective [13] These results highlight the need for a clear definition and description and the psychometric investigation of both proxy perspectives. This lack of information is often neglected in the literature [1, 14,15,16,17,18] and its impact on the validity of the QoL-AD proxy and QoL-AD NH proxy scales is unclear [19]
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