A Differential Item Functioning Analysis of the EQ-5D in Cancer

Measurement properties of the EQ-5D-3L, EQ-5D-5L, and SF-6Dv2 in patients with late-onset Pompe disease

OBJECTIVE

The objective of this study was to evaluate the psychometric properties of the EQ-5D (3L and 5L) and SF-6Dv2 in a group of Chinese patients with late-on Pompe disease (PD), and compare their performance in this patient group.

METHODS

The data used in this study were obtained from a web-based and cross-sectional survey conducted in China. All participants completed the 3L, 5L, and SF-6Dv2. Information about their sociodemographic status and health conditions was also collected. The measurement properties were assessed by examining ceiling and floor effects, evaluating convergent validity, known-group validity, and test-retest reliability (Intraclass correlation coefficient [ICC] and Gwet's AC).

RESULTS

A total of 117 PD patients completed the questionnaire. All dimensions of the 3L showed strong ceiling effects, ranging between 17.1 and 42.7%. All three measures showed good test-retest reliability, with ICC values ranging from 0.85 to 0.87. The Gwet's AC values showed that four out of five dimensions of the 3L showed very good agreement. All hypothesized correlations between the 3L, 5L, SF-6Dv2, and items of WHODAS were supported, indicating satisfactory convergent validity. The 5L showed stronger correlations (|r|= 0.53-0.84) with WHODAS than the other two measures. The outcomes of ANOVA indicated that the 5L had higher F-statistics than the 3L and SF-6Dv2, indicating a stronger discriminant ability to differentiate most condition groups.

CONCLUSION

The 5L demonstrates lower ceiling and floor effects, higher discriminant ability, and better convergent validity than the SF-6Dv2 and 3L in patients with PD. In addition, the 5L may generate a larger utility gain compared to the other two instruments when conducting cost-effectiveness analysis.

Time perspective profile and self-reported health on the EQ-5D

OBJECTIVES

Time perspective (TP) is a psychological construct that is associated with several health-related behaviours, including healthy eating, smoking and adherence to medications. In this study, we aimed to examine the associations of TP profile with self-reported health on the EQ-5D-5L and to detect which domains display response heterogeneity (cut-point shift) for TP.

METHODS

We conducted a secondary analysis of EQ-5D-5L data from a representative general population sample in Hungary (n = 996). The 17-item Zimbardo Time Perspective Inventory was used to measure individuals' TP on five subscales: past-negative, past-positive, present-fatalist, present-hedonist and future. The associations between TP subscales and EQ-5D-5L domain scores, EQ VAS and EQ-5D-5L index values were analysed by using partial proportional odds models and multivariate linear regressions.

RESULTS

Respondents that scored higher on the past-negative and present-fatalist and lower on the present-hedonist and future subscales were more likely to report more health problems in at least one EQ-5D-5L domain (p < 0.05). Adjusting for socio-economic and health status, three EQ-5D-5L domains exhibited significant associations with various TP subscales (usual activities: present-fatalist and future, pain/discomfort: past-negative and future, anxiety/depression: past-negative, present-fatalist, present-hedonist and future). The anxiety/depression domain showed evidence of cut-point shift.

CONCLUSIONS

This study identified response heterogeneity stemming from psychological characteristics in self-reported health on the EQ-5D-5L. TP seems to play a double role in self-reported health, firstly as affecting underlying health and secondly as a factor influencing one's response behavior. These findings increase our understanding of the non-health-related factors that affect self-reported health on standardized health status measures.

Measurement invariance and adapted preferences: evidence for the ICECAP-A and WeRFree instruments

BACKGROUND

Self-report instruments are used to evaluate the effect of interventions. However, individuals adapt to adversity. This could result in individuals reporting higher levels of well-being than one would expect. It is possible to test for the influence of adapted preferences on instrument responses using measurement invariance testing. This study conducts such a test with the Wellbeing Related option-Freedom (WeRFree) and ICECAP-A instruments.

METHODS

A multi-group confirmatory factor analysis was conducted to iteratively test four increasingly stringent types of measurement invariance: (1) configural invariance, (2) metric invariance, (3) scalar invariance, and (4) residual invariance. Data from the Multi Instrument Comparison study were divided into subsamples that reflect groups of participants that differ by age, gender, education, or health condition. Measurement invariance was assessed with (changes in) the Comparative Fit Index (CFI), Root Mean Square Error of Approximation (RMSEA), and Root Mean Square Residual (SRMR) fit indices.

RESULTS

For the WeRFree instrument, full measurement invariance could be established in the gender and education subsamples. Scalar invariance, but not residual invariance, was established in the health condition and age group subsamples. For the ICECAP-A, full measurement invariance could be established in the gender, education, and age group subsamples. Scalar invariance could be established in the health group subsample.

CONCLUSIONS

This study tests the measurement invariance properties of the WeRFree and ICECAP-A instruments. The results indicate that these instruments were scalar invariant in all subsamples, which means that group means can be compared across different subpopulations. We suggest that measurement invariance of capability instruments should routinely be tested with a reference group that does not experience a disadvantage to study whether responses could be affected by adapted preferences.

Analyzing the Pain/Discomfort and Anxiety/Depression Composite Domains and the Meaning of Discomfort in the EQ-5D: A Mixed-Methods Study

OBJECTIVES

The EQ-5D has 2 composite domains: pain/discomfort (PD) and anxiety/depression (AD). This study aims to explore how respondents use the composites to self-report health and what the meaning of discomfort is in the EQ-5D for the general public.

METHODS

Both qualitative and quantitative data were collected in an online cross-sectional survey involving a nationally representative general population sample in Hungary (n = 1700). Respondents completed the 5-level version of EQ-5D, followed by the composites split into individual subdomains. Open-ended questions were asked to explore respondents' interpretations and experiences of discomfort.

RESULTS

Six different response behaviors were identified in the composites: "uniform" (21%-32%), "most severe" (30%-34%), "least severe" (16%-23%), "average" (2%-4%), "synergistic" (4%-5%), and "inconsistent" (13%-15%). Compared with the individual subdomains, many respondents under-reported their problems on both composites (PD 16%-22% and AD 6%-13%, P < .05). In respondents who scored differently in the 2 separate domains, mainly problems with the first subdomain determined responses in the composites (PD 66% and AD 61%). The discomfort subdomain in the EQ-5D captured more than 100 different problems, including pain, nonpain physical discomfort (eg, tiredness, dizziness, and nausea), and psychological discomfort (eg, anxiety, nervousness, and sadness). Women, older adults, and those in worse general health status more often considered discomfort as pain (P < .05).

CONCLUSIONS

We found empirical evidence of measurement error in the composite responses on the EQ-5D, including under- and inconsistent reporting, ordering effects, potential differential item functioning, and interdomain dependency. Our findings contribute new knowledge to the development of new and refinement of existing self-reported health status instruments, also beyond the EQ-5D.

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.

Examination of the measurement equivalence of the Functional Assessment in Acute Care MCAT (FAMCAT) mobility item bank using differential item functioning analyses

OBJECTIVE

To assess differential item functioning (DIF) in an item pool measuring the mobility of hospitalized patients across educational, age, and gender groups.

DESIGN

Measurement evaluation cohort study. Content experts generated DIF hypotheses to guide the interpretation. The graded response item response theory (IRT) model was used. Primary DIF tests were Wald statistics; sensitivity analyses were conducted using the IRT ordinal logistic regression procedure. Magnitude and impact were evaluated by examining group differences in expected item and scale score functions.

SETTING

Hospital-based rehabilitation PARTICIPANTS: 2216 hospitalized patients MAIN OUTCOME MEASURES: 111 self-reported mobility items RESULTS: Two linking items among those used to set the metric across forms evidenced DIF for gender and age: 'difficulty climbing stairs step-over-step without a handrail (alternating feet)' and 'difficulty climbing 3 to 5 steps without a handrail'. Conditional on the mobility state, the items were more difficult for women and older people (aged 65 and over). An additional 18 items were identified with DIF. Items with both high DIF magnitude and hypotheses related to age were difficulty: 'crossing road at a 4-lane traffic light with curbs'; 'jumping/landing on one leg'; 'strenuous activities'; 'descending 3-5 steps with no handrail'. Although DIF of higher magnitude was observed for several items, the scale-level impact was relatively small and the exposure rate for the most problematic items was low (0.35, 0.27 and 0.20).

CONCLUSIONS

This was the first study to evaluate measurement equivalence of the hospital-based rehabilitation mobility item bank. Although 20 items evidenced high magnitude DIF, five related to stairs, the scale-level impact was minimal; however, it is recommended that such items be avoided in the development of short-form measures. No items with salient DIF were removed from calibrations, supporting the use of the item bank across groups differing in education, age, and gender. The bank may thus be useful to assist clinical assessment and decision-making regarding risk for specific mobility restrictions at discharge as well as identifying mobility-related functions targeted for post- discharge interventions. Additionally, with the goal of avoiding long and burdensome assessments for patients and clinical staff; these results could be informative for those using the item bank to construct short forms.

Quality of Life in Palliative Care

Introduction

A main goals of palliative care is to improve the health-related quality of life (QOL) of patients with advanced illnesses. The objective of this narrative review is to provide an updated synopsis on the use of QOL questionnaires in the palliative care setting.

Areas covers

Focusing on the palliative cares setting, we will define QOL, discuss how QOL instruments can be used clinically and in research, review approaches to validate these questionnaires, and how they can be used in utility analyses.

Expert opinion/commentary

Several QOL questionnaires, such as EORTC-QLQ-C30, McGill QOL questionnaire and EQ-5D have been validated in the palliative care setting. However, significant gaps impede their application, including lack of determination of their responsiveness to change and minimal clinically important differences, the need to conduct more psychometric validation on QOL questionnaires among patients at various stages of disease trajectory, and the paucity of studies examining utility and cost-effectiveness. Further research is needed to address these knowledge gaps so QOL questionnaires can be better used to inform clinical practice and research.