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How does a preference-based generic health-related quality of life measure perform in patients with a rare disease? Measurement properties of the EQ-5D-Y proxy version among underage patients with neurofibromatosis type 1

Orphanet Journal of Rare Diseases volume 20, Article number: 71 (2025) Cite this article

Abstract

Background

EQ-5D-Y is a pediatric preference-based health-related quality of life (HRQL) measure that is recommended in health economic evaluation according to China’s guidelines. However, there is limited evidence regarding how the EQ-5D-Y perform in patients with rare diseases in the country. Neurofibromatosis type 1 (NF1) is a rare disease that affects the growth and development of underage patients. This study aimed to examine the performance of EQ-5D-Y proxy version among underage NF1 patients in China.

Methods

Data from a nationwide cross-sectional survey from Nov 2022 to Jan 2023 was used. A total of 154 caregivers for underage NF1 patients who completed the EQ-5D-Y proxy version, PedsQL 4.0 Generic Core Scales (PedsQL GCS) proxy version, and Zarit Burden Interview (ZBI-22) were included. The performance of the EQ-5D-Y was assessed by response pattern (ceiling and floor effects), convergent validity against the PedsQL GCS, known-groups validity, and Shannon (H’) and Shannon evenness (J’) indices.

Result

Data from 154 caregivers were analyzed. The mean age of caregivers was 38.23 (6.02) years, and 78.57% of them were mothers of NF1 patients. The mean age of NF1 patients was 8.38 (3.34) years, with 51.30% being females. The ceiling effect of EQ-5D-Y was 30.52%, and floor effect was 0%. Moderate to strong correlations were found between EQ-5D-Y and PedsQL GCS dimensions that share similar constructs (rho − 0.42 to -0.60, all p values < 0.001). The hypotheses of known-groups defined by different PedsQL GCS and ZBI scores were validated. The EQ-5D-Y exhibited the strongest informativity and discriminatory power of the “feeling worried, sad or unhappy” dimension and weakest for the “mobility” dimension (H’(mobility) = 0.60, J’(mobility) = 0.38; H’(feeling worried, sad or unhappy) = 1.23, J’(feeling worried, sad or unhappy) = 0.78).

Conclusions

EQ-5D-Y is acceptable for measuring HRQL of underage NF1 patients in China. More evidence for using EQ-5D-Y in rare diseases is awaited.

Introduction

There are more than 7,000 rare diseases around the world [1]. Most rare diseases are genetically related, with approximately 70% having childhood-onset [2]. This often results in lifelong physical and psychological distress for both patients and their families [2]. Rare diseases can be life-threatening. The mortality rate for affected individuals under five is around 30% [3]. Neurofibromatosis type 1 (NF1) is a rare disease occurring in every 3000 newborns globally [4]. The clinical manifestations of NF1 can vary widely and may worsen over time. Common symptoms include café-au-lait spots and tumors along nerves affecting multi-systems in the body. While mild cases may only exhibit skin symptoms, severe cases can lead to life-threatening conditions. The dermatological manifestations can affect the psychological health of NF1 patients, while other internal manifestations, such as neurofibromas, can affect their physical health [5]. Rare diseases in China are managed through an officially defined catalog of rare diseases. NF1 is one of the diseases included in China’s Second Catalog of Rare Diseases [6].

In recent years, increasingly number of orphan drugs have been developed [7, 8], bringing hope for patients with rare diseases while usually with high prices. Including expensive orphan drugs in the reimbursement catalog allows more patients with rare diseases to access these medicines, ensuring they truly benefit from them. In many countries such as the UK, Canada, Japan, Australia, Sweden, and China, economic evidence is required for drug reimbursement decision [9,10,11,12]. Cost-utility analysis, which typically employs preference-based health-related quality of life (HRQL) measures, is the most recommended analytical technique for economic evaluation in all those countries mentioned above [13]. However, numbers of pediatric-specific preference-based HRQL measures are limited. Common used pediatric-specific preference-based HRQL measures are EQ-5D-Y, Child Health Utility 9D (CHU9D), and Health Utilities Index (HUI) [14, 15]. According to the pharmacoeconomic evaluation guidelines of the UK, Australia, and China, suitable pediatric-specific HRQL should be used for children in pharmacoeconomic evaluations [13]. China Guidelines for Pharmacoeconomic Evaluations (2020 Edition) specifically pointed out that the EQ-5D-Y is recommended for children [16]. The EQ-5D-Y is the youth version of the EuroQol five-dimensional (EQ-5D) descriptive system, designed for children and adolescents aged 4 to 18 [17]. It features 3 response levels for each dimension to assess physical and mental health. The EQ-5D-Y retains the content and structure of the standard EQ-5D, facilitating a seamless evaluation of health status from childhood into adulthood [18]. EQ-5D-Y is increasingly popularly used to measure HRQL in various pediatric populations [19,20,21,22,23,24].

Even though EQ-5D-Y has been used among patients with NF1 and other rare diseases [17, 25,26,27,28], it hasn’t been validated in China’s NF1 populations. Given China’s large population, the number of NF1 patients is expected to be significant in the country. Assessing measurement properties of the EQ-5D-Y in Chinese patients with NF1 can support medical decision making in this population. The present study aimed to investigate the measurement properties of EQ-5D-Y among underage patients with NF1 in China. The findings will provide insights into the performance of EQ-5D-Y in rare disease populations.

Methods

Data collection

The study used data from a cross-sectional survey conducted from Nov 2022 to Jan 2023. In this survey, primary caregivers for underage NF1 patients were recruited through a nationwide patient group of the NF1 population, Neurofibromatosis Shenzhen Care Center (NSCC). Volunteers from NSCC helped to organize the participants and make preparations for the survey.

As per the ethics committee’s recommendations, all questionnaires in this study should be completed by caregivers of NF1 patients acting as proxies for NF1 patients who were under 18 years old, even though there are varying opinions regarding the consistency between proxy-reported and self-reported HRQL [29,30,31,32]. Early studies showed that the proxy and self-reported versions of EQ-5D-Y and PedsQL GCS generally demonstrate moderate to good agreement [33,34,35,36,37,38,39]. Caregivers were asked to fill out a questionnaire using an online survey platform, where researchers could monitor the entire process of answering the questions. Information on medical treatment (e.g., annual outpatient visit times and hospitalization times) in the year 2021 was collected. The EQ-5D-Y proxy version, PedsQL 4.0 Generic Core Scales (PedsQL GCS) proxy version and Zarit Burden Interview (ZBI-22) were used. The EQ-5D-Y was applicable for caregivers of those patients aged from 4 to 18, and PedsQL GCS was applicable for caregivers of those patients aged from 2 to 18. ZBI-22 was applicable for all the caregivers included. A total of 223 caregivers of NF1 patients were recruited in the cross-sectional survey, only those who completed both the EQ-5D-Y and PedsQL GCS were included in the present study (n = 154).

Ethics approval was obtained from the Ethics Committee of Beijing University of Chinese Medicine (2022BZYLL1005). The study was carried out according to the Declaration of Helsinki. Written informed consent was obtained before the survey began.

Measures

In this study, the EQ-5D-Y proxy version and PedsQL GCS proxy version were used to assess HRQL of underage NF1 patients, and ZBI-22 was used to assess caregiver burden.

EQ-5D-Y

The EQ-5D-Y is a youth version of the EQ-5D descriptive system, designed for children and adolescents aged 4 to 18, and it has a value set for China [17]. Caregivers filled out EQ-5D-Y as proxies only for patients aged between 4 and 18 years old in this study. EQ-5D-Y collects information on one’s health status from three response levels (no problems, some problems, and a lot of problems) of five dimensions: “mobility”, “looking after him/herself”, “doing usual activities”, “having pain or discomfort”, “feeling worried, sad or unhappy” [40]. A visual analog scale (VAS), ranging from 0 to 100, is presented to the respondents after they fill out their health status of five dimensions to get the subjective feeling of their total health. Previous studies demonstrated good validity and reliability of EQ-5D-Y in underage populations [22, 27, 28, 41,42,43].

In the present study, caregivers’ responses to the EQ-5D-Y were converted from the five questions to preference-based EQ-5D utility scores using a value set for EQ-5D-Y in China [17].

PedsQL 4.0 Generic Core Scales

PedsQL GCS is a 23-item HRQL measure for children aged 2 to 18, using 5-point response Likert scales to assess the health status [44]. PedsQL GCS showed good reliability and validity in different populations including NF1 patients and was recommended to be used in neurofibromatosis trials [45,46,47,48,49]. In the present study, caregivers filled out PedsQL GCS proxy version if patients aged between 2 and 18 years old. There are 4 scales in PedsQL GCS assessing HRQL in different domains: (1) physical functioning (8 items), (2) social functioning (5 items), (3) emotional functioning (5 items), and (4) school functioning (5 items). Total score and scale scores of PedsQL GCS were calculated as the average of all the items in the whole PedsQL GCS and each scale and then reversely and linearly transformed into scores ranging from 0 to 100, using the scoring system of the PedsQL questionnaires. A higher PedsQL total score or scale score means a better health status.

Zarit Burden Interview

Zarit Burden Interview (ZBI-22) is a 22-item questionnaire used to measure a caregiver’s burden. ZBI-22 has been used to assess the caregiver burden of different populations including NF1 patients and proved to be valid and reliable [50,51,52,53,54,55]. ZBI-22 uses a 5-level (0–4 points for each item) severity scale to evaluate how the caregiver feels when they provide care for the one being cared for. The total score of ZBI-22 ranges from 0 to 88. The higher the ZBI-22 total score is, the heavier distress a caregiver is experiencing. All caregivers included in the cross-sectional survey filled out ZBI-22.

Data analysis

In the present study, measurement properties of the EQ-5D-Y were assessed by response patterns, construct validity, and informativity and discriminatory power.

Response patterns were demonstrated by ceiling and floor effects, and distribution across response levels of each dimension.

Construct validity included convergent validity and discriminant validity. Convergent validity was examined by Spearman’s correlation coefficient (rho) against the PedsQL GCS. Significant correlations were expected between similar constructs of EQ-5D-Y and PedsQL GCS. At the domain level, similar constructs included EQ-5D-Y “mobility”, “looking after him/herself”, “doing usual activities”, and “having pain or discomfort”, in correspondence to PedsQL physical functioning; “feeling worried, sad or unhappy” in correspondence to PedsQL emotional functioning; “doing usual activities” in correspondence to PedsQL school functioning and social functioning; “doing usual activities”, “having pain or discomfort”, and “feeling worried, sad or unhappy” in correspondence to PedsQL psychosocial health score [56]. Spearman’s correlation was identified as strong correlation (rho > 0.7), moderate correlation (0.4 ≤ rho ≤ 0.7), and weak correlation (rho < 0.4) [57].

Discriminant validity was examined by known-groups validity. When analyzing known-groups validity, we analyzed known-groups as follows: (1) gender; (2) outpatient visit times (< 5 times/year vs. ≥5 times/year); (3) hospitalization times (0 times/year vs. ≥1 time/year); (4) median of ZBI-22 total score; (5) median of PedsQL GCS dimensions and pain scores. These groups are known to differ in health status, and it was anticipated that the EQ-5D-Y utility scores and VAS scores could distinguish children with different health statuses.

Informativity and discriminatory power were examined by Shannon (H’) and Shannon evenness (J’) indices.

In the study, data of EQ-5D-Y, PedsQL GCS, and ZBI-22 need to be complete in order to assess the measurement properties of EQ-5D-Y. Therefore, listwise deletion would be conducted if there was any missing data in EQ-5D-Y, PedsQL GCS, or ZBI-22. We conducted statistical analyses using Stata 17.0 SE. We considered that significant differences exist when p value was ≤ 0.05. Effect size is interpreted as small (Cohen’s d = 0.2), medium (Cohen’s d = 0.5), and large (Cohen’s d = 0.8).

Results

A total of 223 primary caregivers for NF1 patients under 18 years old were recruited in the cross-sectional study. Because the EQ-5D-Y was applied for caregivers of NF1 patients no less than 4 years old, a total of 154 caregivers responded to all the three HRQL instruments (EQ-5D-Y, PedsQL GCS, and ZBI-22) and were included in the present study (Table 1). Since the data was collected by a one-on-one online survey to guarantee the quality of the research, participants in the study were required to answer all questions of EQ-5D-Y, PedsQL GCS, and ZBI-22 that were applicable. Therefore, there was no missing response of EQ-5D-Y, PedsQL GCS, or ZBI-22 in the present study.

Table 1 Characteristics of participants
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Response pattern

At the health state level, 30.52% of the respondents reported no problems in all five dimensions of EQ-5D-Y (“11111” state), which meant the overall ceiling effect for EQ-5D-Y was 30.52%. None of the respondents reported the most severe state in all five dimensions of EQ-5D-Y (state “33333”), which meant there was no floor effect for EQ-5D-Y (Table 2). At the dimension level, the proportion of the respondents who reported having problems was 11.69% for “mobility (waking about)”, 17.53% for “looking after himself/herself” and 27.92% for “doing usual activities”, 52.60% for “having pain or discomfort”, and 42.86% for “feeling worried, sad or unhappy”. The mean (SD) of EQ-5D-Y utility scores was 0.880 (0.133), and the mean (SD) of VAS scores was 75.38 (20.67).

Table 2 Response pattern of EQ-5D-Y, PedsQL GCS and ZBI-22 (n = 154)
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Convergent validity

EQ-5D-Y utility had a strong correlation with the PedsQL GCS total score (rho = 0.72, p < 0.001) and was moderately correlated with PedsQL GCS domains (rho range 0.59 to 0.68, p < 0.001 for all) (Table 3). EQ-5D VAS was moderately correlated with PedsQL total score and domains (rho range, 0.47 to 0.60, p < 0.001 for all).

For EQ-5D-Y dimensions and PedsQL GCS scales, which measure similar constructs, the EQ-5D-Y “mobility” and PedsQL GCS physical functioning were moderately correlated (rho = -0.45, p < 0.001). Besides, “looking after him/herself”, “doing usual activities”, and “having pain or discomfort” in the EQ-5D-Y were moderately correlated (rho range, -0.42 to -0.60, p < 0.001 for all) with the PedsQL GCS physical functioning. The EQ-5D-Y “feeling worried, sad or unhappy” and PedsQL GCS emotional functioning were moderately correlated (rho = -0.45, p < 0.001). The EQ-5D-Y “doing usual activities” and PedsQL GCS school functioning were moderately correlated (rho = -0.42, p < 0.001). “Having pain or discomfort” (rho = -0.56, p < 0.001) and “feeling worried, sad or unhappy” (rho = -0.48, p < 0.001) were moderately correlated with PedsQL GCS psychosocial health score. The psychosocial health score was calculated as the average of scores in emotional functioning, social functioning, and school functioning.

Table 3 Spearman’s correlation coefficients between EQ-5D-Y and PedsQL GCS at domain level
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Known-groups validity

EQ-5D-Y utility scores of patients who had outpatient visits more than 5 times in 2021, who had lower PedsQL GCS total scores and scale scores or who had higher ZBI-22 total scores, were lower than their counterparts, with effect sizes of medium to large magnitude (Table 4) [58]. EQ-5D VAS scores of patients who had lower PedsQL GCS total scores and scale scores or who had higher ZBI-22 total scores, were lower than their counterparts, with effect sizes of medium to large magnitude.

Table 4 Known group analysis
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Informativity and discriminatory power

The Shannon index and Shannon evenness index of the EQ-5D-Y dimensions were 0.60 and 0.38 for “mobility”, 0.79 and 0.50 for “looking after him/herself”, 0.98 and 0.62 for “doing usual activities”, 1.20 and 0.76 for “having pain or discomfort”, 1.23 and 0.78 for “feeling worried, sad or unhappy” (Table 5).

Table 5 Shannon index and Shannon evenness of EQ-5D-Y
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Discussion

Although measurement properties of HRQL measures in rare disease patients are increasingly the focus of researchers, the present study was the first study analyzing the measurement properties of EQ-5D-Y against PedsQL GCS among underage NF1 patients in China, to our knowledge. We observed the measurement properties of the EQ-5D-Y proxy version based on cross-sectional survey data which evaluated the HRQL among children with NF1, reported by their caregivers [59]. Reliable and widely recognized validation methods were employed. Drawing on data from a survey of 154 caregivers as proxies of children with NF1, EQ-5D-Y showed strong consistency with PedsQL GCS. The known-group hypotheses based on varying PedsQL GCS and ZBI scores were validated. The “feeling worried, sad, or unhappy” dimension of EQ-5D-Y displayed the highest Shannon index and Shannon evenness index. The findings indicate that the EQ-5D-Y is a reliable and efficient preference-based tool for evaluating HRQL in this population.

According to a study validated pediatric preference-based HRQL instruments (EQ-5D-Y and CHU9D), validation of EQ-5D-Y was suggested to be conducted among the population with 10 diseases, including anxiety/depression, attention deficit hyperactivity disorder (ADHD), autism, and recurrent abdominal pain, three of which were related to pain, and some were closely associated with psychological health [60]. The common symptoms of these ten diseases align closely with the dimensions of EQ-5D-Y. Therefore, the author stated that these 10 diseases may be suitable for studies describing the measurement properties of EQ-5D-Y. Some underage NF1 patients have manifestations of pain, and clinical symptoms that affect their physical appearance may lead to psychological distress. These disease manifestations in patients with NF1 are aligned with the dimensions of EQ-5D-Y. Therefore, we inferred that underage NF1 patients may serve as an appropriate population for assessing the measurement properties of EQ-5D-Y.

Based on the 154 study samples, the ceiling effect and the floor effect of EQ-5D-Y were 30.52% and 0%, respectively. The high ceiling effect observed in this study may be explained by the fact that many NF1 patients exhibit only mild skin symptoms. In previous studies, ceiling effects of EQ-5D-Y proxy version were reported ranging from 45 to 68% in different populations, such as the general population, patients with renal and urinary diseases, or patients with metabolism and nutrition disorders [21, 33, 61,62,63,64]. The EuroQol Group developed EQ-5D-Y-5L, a revised version of EQ-5D-Y that extends the response levels from 3 to 5 levels in each dimension [65, 66]. The EuroQol Group believes that EQ-5D-Y-5L would reduce the ceiling effects and enhance the sensitivity of EQ-5D-Y, which needs to be further assessed in NF1 population.

As for convergent construct validity, results of the present study suggested that EQ-5D-Y proxy version has acceptable convergent construct validity in the population of underage NF1 patients. EQ-5D-Y utility and PedsQL GCS total score were highly related (Spearman’s rho = 0.72), exceeding previously reported correlation coefficients, which ranged from 0.20 (in mostly healthy children) to 0.66 (in acutely ill children) [19, 64, 67,68,69,70]. This Spearman’s correlation coefficient observed in our study is on the upper bound of previous literature values. One possible reason is that, according to the calculation formula of Spearman’s correlation, the high ceiling effect of the EQ-5D-Y results in more frequent rank ties, which in turn lowers the Spearman correlation coefficient [71, 72]. Compared to our results, previous studies with a higher ceiling effect usually reported a lower Spearman’s correlation between EQ-5D-Y utility and PedsQL total scores [64, 69].

Results of known-groups validity indicated that EQ-5D-Y did have the ability to discriminate between underage patients defined by the subgroups which were set according to the presupposition that different HRQL levels were known to be observed. These hypotheses of known groups “annual outpatient visit times” and “annual hospitalization times” were not confirmed. We initially used these to reflect the severity of the disease indirectly because there was a lack of clinical information for the patients. The DNB classification (dermatological, neurological and bone manifestations) and imaging examination like magnetic resonance imaging (MRI) can tell the severity of NF1 in a more direct way [73]. It would be better if clinical information on NF1 patients, such as MRI and the number of neurofibromas, be collected to assess the severity of the disease in future studies on the performance of EQ-5D-Y.

In this study, we can only assess the measurement properties of EQ-5D-Y proxy version. Measuring HRQL is a complex process that requires consideration of various factors. Some HRQL measures showed good agreement and consistency between reports from proxies and self-reports, while others did not [29,30,31, 74]. For the same HRQL measure, proxy-reported versions may sometimes overestimate HRQL in certain populations and underestimate it in others [30, 75,76,77]. Caregivers, often acting as proxies, may have their assessments of HRQL influenced by factors such as their own gender and health status [76, 77]. For those patients over 8 years old, it is recommended that the self-reported version of EQ-5D-Y is a better choice [40]. How the older children perceive their health is important and can provide more direct information [78], which need to be investigated in future studies.

Limitations

There are some limitations in the present study. Only construct validity and discriminatory power could be examined since the study’s data were from a cross-sectional survey. Test-retest reliability needs to be assessed in future studies. Feasibility, which can be examined by the missing rate and the overall time taken to finish EQ-5D-Y, was not investigated in the present study since we use the one-on-one online design to conduct the survey and necessary questions of the EQ-5D-Y and PedsQL GCS were set as required questions, except for those questions that were claimed to be optional.

For ethical reasons, only proxy versions of EQ-5D-Y and PedsQL GCS were used in this study. We expected to investigate the performance of self-reported EQ-5D-Y and other HRQL instruments among NF1 patients in future studies.

Conclusion

Overall, EQ-5D-Y is an acceptable choice to evaluate the HRQL of NF1 patients as it is a short preference-based HRQL measure, with significant advantages of time-saving, and results can be used to calculate quality-adjusted life years in economic evaluation. Further validation of HRQL measures among underage NF1 patients using longitudinal data and based on self-report data will provide more information. More evidence of validation and reliability of EQ-5D-Y among different populations is expected.

Data availability

The datasets used in this study are not publicly available due to privacy concerns. However, interested individuals can request access to the data from the corresponding author, subject to approval by Beijing University of Chinese Medicine.

Abbreviations

ADHD:

Attention deficit hyperactivity disorder

EQ-5D:

EuroQol five-dimensional

HRQL:

Health-related quality of life

MRI:

Magnetic resonance imaging

NSCC:

Neurofibromatosis Shenzhen Care Center

NF1:

Neurofibromatosis type 1

PedsQL GCS:

PedsQL 4.0 Generic Core Scales

VAS:

Visual analog scale

ZBI-22:

Zarit Burden Interview

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Acknowledgements

We sincerely acknowledge the contribution of the volunteers from Neurofibromatosis Shenzhen Care Center during the data collection and support from all the caregivers for underage NF1 patients who participated in the cross-sectional survey.

Funding

The work was based on the data collected from a cross-sectional survey sponsored by the China Alliance for Rare Diseases and the Beijing Society of Rare Disease Clinical Care and Accessibility. The work was also sponsored by Beijing Nova Program (No. Z211100002121060).

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Authors and Affiliations

  1. Center for Evidence-Based Chinese Medicine, School of Traditional Chinese Medicine, Beijing University of Chinese Medicine, Beijing, China

    Wanxian Liang, Shihuan Cao, Yusi Suo, Lining Zhang, Lujia Yang, Hanfei Wang, Han Wang & Xuejing Jin

  2. International Institute of Evidence-Based Traditional Chinese Medicine, Beijing University of Chinese Medicine, Beijing, China

    Wanxian Liang, Shihuan Cao, Yusi Suo, Lining Zhang, Lujia Yang, Hanfei Wang, Han Wang & Xuejing Jin

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Contributions

XJ and WL contributed to the study design. Data collection was performed by WL, SC, YS, LZ, and LY. WL conducted the statistical analysis. The draft of the manuscript was written by WL under XJ’s supervision. XJ, HW, YS, and HW critically revised the manuscript. All authors read and approved the final manuscript.

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Correspondence to Xuejing Jin.

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Ethics approval and consent to participate

The study was approved by the Ethics Committee of Beijing University of Chinese Medicine (2022BZYLL1005) and was carried out according to the Declaration of Helsinki. Electronically signed informed consent was obtained before the survey began.

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Not applicable.

Competing interests

XJ is a member of EuroQol Group Association. Other authors declare that they have no conflict of interest.

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Liang, W., Cao, S., Suo, Y. et al. How does a preference-based generic health-related quality of life measure perform in patients with a rare disease? Measurement properties of the EQ-5D-Y proxy version among underage patients with neurofibromatosis type 1. Orphanet J Rare Dis 20, 71 (2025). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s13023-025-03590-x

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Keywords

Orphanet Journal of Rare Diseases

ISSN: 1750-1172