Quality of Life Ratings and Proxy Bias in Primary Progressive Aphasia: Two Sides to the Story?

Abstract

A valid measure of quality of life is important for clinical goal setting and for evaluating interventions. In the amnestic dementias, proxy-raters (e.g. friends, families, clinicians) typically rate quality of life lower than the self-ratings given by the person with dementia - a proxy bias. This study investigated whether the same proxy bias occurs in Primary Progressive Aphasia (PPA), a language-led dementia.Quality of life was measured in 18 individuals with PPA using self-ratings, and proxy-ratings by their main communication partner, using the Quality of Life in Alzheimer's Disease Scale.There was no strong evidence for proxy bias at a group level, with no consistent pattern across dyads, where proxy- and self-ratings did not show good levels of agreement. We suggest that self-ratings and proxy-ratings of quality of life in PPA are not interchangeable. Higher-powered investigation of the patterns observed here is warranted in future studies.

Keywords: aphasia; dementia; primary progressive aphasia; proxy; quality of life; ratings; wellbeing.

Figure 1.

Average Ratings for Each QOL-AD Item for Ratings by People with PPA (self-rated QOL-AD) and their Proxies. Note: Figure is ordered from the item with least advantage for self-rated scores over proxy-rated scores (i.e., least proxy bias) to most advantage (i.e. greatest proxy bias). Bars indicate standard error. Y-axis shows rating scale for each item where 1 = Poor, 2 = Fair, 3 = Good and 4 = Excellent. For the item ‘Marriage’, n = 15 whereas for all other items n = 18, due to three dyads not being married and declining to rate the item on another proxy.

Figure 2.

Bland-Altman plot for QOL-AD total scores rated by people with PPA and proxies. Note: Bias: The average difference between patient and proxy (or ‘bias’) is indicated by the red line with accompanying confidence intervals (dotted red lines). A difference of 0 (the x-axis) would indicate perfect agreement. If the x-axis falls outside of the confidence interval of the bias, this would indicate significant rater bias is occurring; significant rater bias is not seen in this plot. Agreement: Limits of agreement (green dashed lines) indicate the area from +1.96 SD to -1.96 SD, within which 95% of the data lie, and require clinical interpretation.

Figure 3.

Differences in quality of life ratings across dyads. Note: Dyads have been ordered by degree of proxy bias, i.e. the left side of the figure shows dyads where the person with PPA rated their quality of life lower than their proxy did (a reverse proxy bias) and the right side shows dyads where the person with PPA rated their quality of life higher than their proxy (greatest proxy bias).