Development and Psychometric Validation of the 27 Item Zarit Caregiver Interview for Alzheimer's Disease (ZCI-AD-27)

Abstract

Background: Caring for an individual with Alzheimer's disease (AD) is an allencompassing challenge that affects daily life. Assessment of the care partner experience is needed to support the development and evaluation of successful interventions for people with AD and their care partners. We developed the 27-item Zarit Caregiver Interview for Alzheimer's Disease (ZCI-AD-27) to assess the impact of informal caregiving in the context of AD.

Objective: We assessed the psychometric validity of the ZCI-AD-27 in a population of care partners for individuals with moderate AD, and established thresholds for meaningful score change.

Methods: Secondary data were obtained from informal care partners of participants in a clinical trial (NCT01677754). Psychometric analyses were conducted to assess validity, reliability, and responsiveness of the ZCI-AD-27. Anchor-based and distribution-based methods were performed to determine clinically meaningful score change.

Results: The ZCI-AD-27 had a 12-domain factor structure, including a second-order domain termed Humanistic impact that included four key domains (Physical, Emotional, Social, and Daily life) as confirmed by confirmatory factor analysis with the adequate fit. Internal consistency (Cronbach's alpha ranging from 0.66 to 0.93 for domains), convergent validity, and discriminant validity indicated the good performance of the ZCI-AD-27. Known-groups validity analyses showed a greater impact on care partners with increasing disease severity. Responsiveness results demonstrated that the ZCI-AD- 27 is sensitive to change over time and meaningful change analyses indicated a range of meaningful score changes in this population.

Conclusion: The ZCI-AD-27 is a comprehensive, psychometrically valid measure to assess the impact of caring for individuals with moderate AD.

Keywords: Alzheimer’s disease; Zarit Burden Interview; Zarit Caregiver Interview; caregiver; caregiverreported outcomes; psychometrics; validation.

Fig. (1)

Confirmatory factor analysis results of the final 12-domain model of the ZCI-AD-27 and the second-order Humanistic impact domain linking items and concepts at baseline (N = 519). Abbreviations: AGFI, Adjusted Goodness of Fit Index; CFI, Comparative Fit Index; GFI, Goodness of Fit Index; NA, not applicable; NFI, Normed Fixed Index; RMSEA, Root Mean Square Error of Approximation; SRMR, Standardized Root Mean Square Residuals; ZCI-AD-27, Zarit Caregiver Interview - Alzheimer’s Disease-27.

Fig. (2)

Comparison of ZCI-AD-27 scores with the GDS at baseline.* Note: * N = 519. ^a The MAyflOwer RoAD study recruited moderate AD patients with an MMSE score ranging from 13-20. This graph displays grouping at BL for known-groups validity analyses according to the Global Deterioration Scale; a clinician-rated assessment of cognitive impairment (see supplementary materials for scale description). A small number of patients (n = 64) fell into the mild group, likely reflecting that some of the patients recruited into the MAyflOwer study according to their performance on a cognitive test (MMSE range of 13-20) were in fact, at the milder end of the AD spectrum according to clinician-rated assessment. Indeed, Balsis et al. (2015) [34] demonstrated that a score of 20 on the MMSE corresponds to a score of 6.5 on the CDR-SB, which in turn falls into the range of scores associated with a CDR-Global score of 1 (CDR-SB range 4.5-9 = CDR-GS 1), reflecting mild AD [35]. Abbreviations: CI, confidence interval; GDS, Global Deterioration Scale; ZCI-AD-27, Zarit Caregiver Interview - Alzheimer’s Disease-27.

Fig. (3)

Comparison of ZCI-AD-27 scores according to the BEHAVE-AD-FW global rating at baseline.* Note: * N = 519. Abbreviations: BEHAVE-AD-FW, Behavioral Pathology in Alzheimer’s Disease Frequency - Weighted Severity Scale; CI, confidence interval; ZCI-AD-27, Zarit Caregiver Interview - Alzheimer’s Disease-27.

Fig. (4)

Change in ZCI-AD-27 scores from baseline to Week 52 according to the CaGI-AD change in experience item.* Note: *N = 312. Abbreviations: CaGI-AD, Caregiver Global Impression of Change in Alzheimer’s Disease; CI, confidence interval; ZCI-AD-27, Zarit Caregiver Interview - Alzheimer’s Disease-27.