Individual and Dyadic Health-Related Quality of Life of People Living with Dementia and their Caregivers

Many interventions target dyads of people living with Alzheimer’s disease and related dementias (ADRD) and their caregivers. Without a dyadic measure of health-related quality of life (HRQOL), cost-utility analyses of these interventions require using the HRQOL of people with ADRD and caregivers, separately. We developed a dyadic measure of HRQOL that incorporates the interdependence between HRQOL of people living with ADRD and their caregivers and measures the dyad’s collective benefits. First, we estimated dyadic HRQOL time trade-off-weights (TTO-weights), a dyadic preference-based measure of HRQOL. Second, we estimated the association between ADRD clinical features and TTO-weights. We used the Aging, Demographics, and Memory Study to identify people living with ADRD (n = 308) and their caregivers (n = 160 dyads) and predict their TTO-weights. We estimated dyadic TTO-weights using an Archimedean bivariate utility copula with a quadratic generating function. Finally, we used adjusted linear regression to examine the association between predicted TTO-weights and ADRD clinical features. Average (standard deviation) TTO-weights of people living with ADRD, and caregivers were 0.67 (0.14) and 0.83 (0.09), respectively. Average dyadic TTO-weight was 0.75(0.05). When the dyadic TTO-weight was ≤ 0.60, an increase in the TTO-weight of the dyad-member with the lowest HRQOL resulted in a larger gain in the dyadic TTO-weight than a similar increase in the TTO-weight for the dyad-member with the higher baseline TTO-weight (i.e., non-proportional tradeoffs). When the dyadic TTO-weight is > 0.60, an increase in the TTO-weight for either member of the dyad increases the dyad TTO-weight equally (constant tradeoffs). An additional functional limitation resulted in more than twice the decline in the TTO-weight of people living with ADRD compared to an additional behavioral symptom (-0.008 vs. -0.003). Behavioral symptoms were significantly associated with a decline in caregivers’ and dyadic TTO-weights. The HRQOL of people living with ADRD and their caregivers are correlated. The dyadic TTO-weights for people living with ADRD and their caregivers can be used in cost-utility analyses to assess the collective gains in HRQOL and tradeoffs of interventions that target members of the dyad.