An Investigation of Age-Related Differential Item Functioning in the EQ-5D-5L Using Item Response Theory and Logistic Regression.

OBJECTIVES: In economic evaluations, quality of life is measured using patient-reported outcome measures (PROMs), such as the EQ-5D-5L. A key assumption for the validity of PROMs data is measurement invariance, which requires that PROM items and response options are interpreted the same across respondents. If measurement invariance is violated, PROMs exhibit differential item functioning (DIF), whereby individuals from different groups with the same underlying health respond differently, potentially biasing scores. One important group of healthcare consumers who have been shown to have different views or priorities over health is older adults. This study investigates age-related DIF in the EQ-5D-5L using item response theory (IRT) and ordinal logistic regression approaches. METHODS: Multiple-group IRT models were used to investigate DIF, by assessing whether older adults aged 65+ years and younger adults aged 18 to 64 years with the same underlying health had different IRT parameter estimates and expected item and EQ-5D-5L level sum scores. Ordinal logistic regression was also used to examine whether DIF resulted in meaningful differences in expected EQ level sum scores. Effect sizes examined whether DIF indicated meaningful score differences. RESULTS: The anxiety/depression item exhibited meaningful DIF in both approaches, with older adults less likely to report problems. Pain/discomfort and mobility exhibited DIF to a lesser extent. CONCLUSIONS: When using the EQ-5D-5L to evaluate interventions and make resource allocation decisions, scoring bias due to DIF should be controlled for to prevent inefficient service provision, where the most cost-effective services are not provided, which could be detrimental to patients and the efficiency of health budgets.

A Qualitative Investigation of Older Adults' Conceptualization of Quality of Life and a Think-Aloud Content Validation of the EQ-5D-5L, SF-12v2, Warwick Edinburgh Mental Wellbeing Scale, and Office of National Statistics-4.

OBJECTIVES: Old age is characterized by declining health, comorbidities, and increasing health and social care service use. Traditionally, patient-reported outcome measures (PROMs) including the EQ-5D-5L and SF-12v2 have focused on health. Nevertheless, aged care often aims to improve broader elements of quality of life (QoL), captured by well-being measures, such as the Warwick Edinburgh Mental Wellbeing Scale (WEMWBS) and Office of National Statistics-4 (ONS-4). This study investigates older adults' conceptualization of QoL and the content validity of the EQ-5D-5L, SF-12v2, WEMWBS, and ONS-4 in measuring their QoL. METHODS: Qualitative cognitive think-aloud interviews were undertaken with older adults aged 75+, exploring their views on what was important to QoL and, for each measure, the relevance, acceptability, and interpretation of items; suitability of response options; and the comprehensiveness of the measure. Conceptualization of QoL was analyzed thematically and content validity using framework analysis. RESULTS: Twenty interviews were undertaken. Older adults' conceptualization of QoL centered on health, ability to perform usual activities, social contact, and emotional functioning. Possible response shift was observed, as older adults assessed their health relative to lower health expectations at their age or to people in worse states. Participants questioned the relevance of negatively phrased mental items and often preferred the functioning-focused EQ-5D-5L to more subjective ONS-4 and WEMWBS items. Domains suggested to improve comprehensiveness included social contact, coping, security, dignity, and control. CONCLUSIONS: These findings are useful to researchers developing new PROMs for older adults or for the developers of included PROMs considering permanently adapting or bolting-on domains to improve content validity in older adults.