3 Ethnoracial Differences in Anchor Agreement and MCID Estimation in Alzheimer’s Disease

Abstract

Objective:

Alzheimer’s disease (AD) clinical trials lack diverse representation, limiting their generalizability. In addition, the clinical meaningfulness of observed changes during treatment may vary as a function of participant characteristics. Defining meaningful change in AD within diverse ethnoracial groups is therefore greatly needed. Meaningful change in AD trials can be assessed by three different anchors: participants, informants, or clinicians. Previous research has suggested that estimations of the minimal clinically important difference (MCID) vary by disease severity, choice of anchor, and anchor agreement. These relationships have been studied primarily within non-Hispanic white (NHW) samples. This project evaluates anchor-based MCID within and across the three most prevalent ethnoracial groups in the United States, non-Hispanic White (NHW), Hispanic/Latino (H/L), and Black/African-American (B/AA).

Participants and Methods:

Data from the National Alzheimer’s Coordinating Center Uniform Dataset (NACC UDS) were used to investigate MCID within older adults (ages 50+) diagnosed as cognitively normal or cognitively impaired due to suspected AD. Data were taken from all versions of the UDS and consisted of all available participants with two consecutive annual visits. The identified sample (N=22,043) is approximately 83.6% NHW, 4.7% H/L, and 11.7% B/AA. Participant, informant, and clinician anchor variables were utilized to compare proportions of anchor agreement within and across ethnoracial groups. MCID on the Mini-Mental State Exam (MMSE) was estimated within each ethnoracial group and compared across the independent variables of anchor agreement and disease severity (cognitively normal (CN), mild cognitive impairment (MCI), and dementia) in 2x3 ANOVAs.

Results:

Participant age (M = 71.56, SD = 9.03) did not significantly differ across ethnoracial groups; years of education significantly differed across groups, p < .001, with NHW (M=15.83 SD=3.05), H/L (M=12.49, SD=5.01), and B/AA (M=14.42, SD=3.22). Across all three anchors (participant, informant, clinician), unanimous agreement about the presence or absence of a decline in functioning was present in about 75.1% of the full sample. To further explore agreement differences across groups, anchor agreement was classified into a 3-level variable: 1) agreement that the participant remained stable over time, 2) agreement that the participant declined, and 3) disagreement. The proportion of each level within each ethnoracial group was significantly different, (x²(4, n = 22,043) = 179.16, p < .001, phi = .09, NHW (34.5% agreement-stable, 41.4% agreement-declined, 24.1% disagreement), H/L (30.5%, 42.6%, 26.9%, respectively), and B/AA (42.2%, 28.1%, 29.7%, respectively). MCID estimates on the MMSE followed similar trends within each ethnoracial group. There was a significant main effect of disease severity, such that MCID estimates increased in magnitude with increasing disease severity. There were no significant main effects of anchor agreement for any ethnoracial group. Within the NHW sample only, an interaction effect between diagnostic severity and anchor agreement was significant (p = .007).

Conclusions:

Across ethnoracial groups, MCID estimates on the MMSE are reliably influenced by the severity of disease. However, the benefit of anchor-based MCID estimates may vary by ethnoracial group with respect to both anchor choice and use of anchor agreement. The origins of anchor disagreement and perceived stability in functioning warrant further exploration.