Comparing the psychometric properties of EQ-5D-3L and EQ-5D-5L proxy ratings by informal caregivers and a health professional for people with dementia

Overview

The EQ-5D-3L, the EQ-5D-5L, the EQ-visual analogue scale (VAS) and the Quality of Life in Alzheimer's Diseases (QoL-AD) were completed as proxy ratings by family caregivers and care manager. Both versions of the EQ-5D were compared in terms of acceptability, agreement, ceiling effects, redistribution properties, inconsistency, informativity, and convergent and discriminative validity.

Study design and recruitment

This study used data collected from the ongoing interventional study DCM:IMPact (Dementia Care Management: Implementation into different Care Settings), an implementation study, which builds on the DelpHi-trial (Dementia: Life- and person-centred help in Mecklenburg-Western Pomerania, Germany) [23]. The mixed-methods, multi-center, implementation study DCM:IMPact was initiated to evaluate the effectiveness and efficiency of collaborative dementia care [23, 24]. Effective [25] and cost-effective [26] dementia care management intervention was implemented in various care settings (e.g. physician networks, nursing care centers) to disclose which care setting would reveal the highest need and lowest implementation barriers for such models of care and, thus, where the best effects could be achieved.

Health care professionals assessed patients' eligibility (70 years or older, living at home, screened positive for dementia or received a formal dementia ICD-10 diagnosis). If patients were eligible, the professionals provided written and oral information about the study and asked for patient and caregiver written informed consent (IC). This study was approved by the local ethics committee at the University Medicine Greifswald (BB 01/2019).

This analysis was based on preliminary data, including n = 77 patients, n = 52 caregivers and one dementia care manager, who had provided collaborative dementia care management for six months. Data were assessed at baseline and three and six months after the baseline assessment.

Data assessment

The EQ-5D-3L, the EQ-5D-5L, the EQ-VAS [18, 19, 27, 28], and the QoL-AD [29] were administered as proxy ratings via standardized computer-assisted face-to-face interviews. Thus, caregivers completed the measures via interview administrations at the caregivers' home done by a specifically-qualified nurse, the care manager. The care manager subsequently self-completed the EQ-5D-3L and 5L.

The informal caregivers and the care manager first completed the EQ-5D-3L with the EQ-VAS, followed by the completion of the EQ-5D-5L and the QoL-AD. Thus, for the caregiver, the "Interviewer Administered Proxy version 1" were used where the interviewer asked the caregiver (proxy) to rate the patient's health-related quality of life in their (the proxy's) opinion. For the care manager, we used the "Proxy version 1", where the care manager (the proxy) was asked to rate the patient's health-related quality of life in their (the proxy's) opinion. Interviews of the caregivers conducted by care manager were done first before the care manager themself completed the EQ-5D-3L and 5L.

Health-related quality of life and clinical instruments

The EQ-5D is a generic HRQoL instrument containing three (no, some, and extreme problems) or five levels (no, slight, moderate, severe, and extreme problems) for the following five dimensions: mobility, self-care, pain/discomfort, usual activities, and anxiety/depression. The responses to the EQ-5D-3L were converted to health utilities, the preference-based single index measure for HRQoL anchored at 0 for death and 1 for full health [18, 19, 27, 28]. The QoL-AD is a dementia-specific HRQoL instrument consisting of 13 items (eg, physical health, living situation, family, mood, energy, cognition, relationships, activities, etc.) using a scale of 1–4 (poor, fair, good, or excellent). Results of the QoL-AD are presented as a sum score, ranging from 13 to 52. Higher scores indicate better quality of life [29].

The following sociodemographic and clinical data were assessed: cognitive impairment measured with the Mini-Mental State Examination (MMSE) [30], comorbidity assessed with the number of ICD-10 (International Statistical Classification of Diseases and Related Health Problems) diagnoses listed in the GP files [31] and the response to the Charlson Comorbidity Index [32], social functioning [33] and depression based on the Geriatric Depression Scale (GDS) [34], deficits in daily living activities based on the Bayer Activities of Daily Living (B-ADL) Scale [35], healthcare resource utilization, e.g. hospitalization, by application of the Resource Utilization in Dementia Questionnaire (RUD) [36], general mental and physical health (the dementia care manager subjectively categorized the patients' general health after completion of the intervention into one of the categories: very good, good, poor), and severity of pain assessed with the standardized assessment of older adults in primary care (STEP) [37].

Data analyses

The responses to the EQ-5D-3L and EQ-5D-5L were converted to health utilities with the European and German value set [28, 38], respectively. The European value set of preference weights scores were applied to generate a VAS-based weighted health status index for all the potential 243 EQ-5D health states, ranging from 1 to − 0.074. The German value set is based on time trade-off and discrete choice experiments to estimate values for all 3125 possible health states, ranging from − 0.661 to 1. Descriptive statistics were used to present sociodemographic and clinical data for the study population. Measurement properties of the EQ-5D-3L and EQ-5D-5L were assessed in terms of acceptability, ceiling effects, agreement, redistribution properties, inconsistency, informativity, discriminative ability, and convergent validity.

Missing values and floor/ceiling effects

The number of missing values, the score ranges (observed vs. possible range), and the floor (% with lowest possible score) and ceiling effects (% with highest possible score) were used to compare the acceptability of both instruments. Additionally, absolute and relative changes in the ceiling effect of EQ-5D-3L versus EQ-5D-5L were calculated.

Agreement

The agreement between both versions was assessed with intraclass correlations (ICC) and presented with Bland–Altman plots. The ICC represents the proportion of variance from both index scores attributable to differences between individuals instead of the differences between the EQ-5D-3L and 5L. The higher the ICC, the higher agreement between the two versions. ICC higher (lower) than 0.7 indicates an acceptable (poor) agreement.

Redistribution properties and inconsistency

Inconsistency was assessed as suggested by previous studies [20, 39, 40], which defined a response within one EQ-5D domain as inconsistent when an answer in the three-level version is at least deviated two levels from the answer given in the five-level version (for example, 12,111 in the 3L version and 14,111 in the 5L version). The inconsistency size could thus range from 1 (two-level difference) to 3 (four-level difference). Redistribution properties were calculated as the percentage of consistent and inconsistent 3L–5L response pairs and the average size of inconsistency for each dimension and displayed with cross-tabulation of dimension scores.

Informativity

The informativity of both measures was assessed with Shannon indices (i.e. Shannon–Weaver index (H') and Shannon's evenness index (J')), which are appropriate measures to determine the discriminatory ability in health state classification in the comparison of the EQ-5D-3L and EQ-5D-5L. The higher the Shannon H' index, the more absolute information is captured by the measures. The Shannon Evenness index (J') captures the relative informativity of the distribution measure, regardless of the number of categories [20, 41]. If a cognitively impaired patient would not complete the additional levels as part of the 5L, relative informativity would be decreased, i.e. an expression of a loss of potential informativity [20, 42]. Discriminative power (change in absolute and relative informativity) was estimated for each dimension and the overall classification system. Positive (negative) values will demonstrate a gain (loss) of absolute and potential informativity of the 5L compared to the 3L version.

Known groups validity

The discriminative ability, defined as the ability to distinguish between different health and diseases stages, was assessed by different stages of functional impairment (Bayer Activities of daily living), cognitive impairment (Mini-Mental State Examination), depression (Geriatric depression scale) as well as general physical and mental health status. Cut-off values used for this analysis were established and validated within the development of each measure. Linear trends were assessed with the nonparametric Jonckheere trend test (> 3 groups) or Mann–Whitney test (2 groups).

Convergent validity

Convergent validity was assessed with Spearman's Correlation Coefficient between the EQ-5D-3L and EQ-5D-5L with the QoL-AD. Due to some overlap of dimensions (i.e. physical health, usual activities, self-care), we assumed there should be a moderate correlation between these measures. A correlation coefficient higher than 0.3 and 0.5 was determined as a moderate and strong correlation, respectively [43]. There should be a positive (negative) correlation between EQ-5D dimensions and B-ADL and GDS (EQ-VAS and QoL-AD) scores, as well as positive (negative) correlations between EQ-5D utility index and B-ADL and GDS (EQ-VAS and QoL-AD) scores.

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