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Phys. Ther. Korea 2023; 30(1): 32-40

Published online February 20, 2023

https://doi.org/10.12674/ptk.2023.30.1.32

© Korean Research Society of Physical Therapy

Equating Two Health-related Quality of Life Instruments Applied to Cancer Survivors Who Underwent Palliative Care

Bongsam Choi1 , PT, MPH, PhD, Heesu Kim2 , PT, BS, Sunhwi Bang3 , KMD, Byunggwan Kim4 , PT, Jaekwang Shim5 , PT, PhD

1Department of Physical Therapy, College of Health and Welfare, Woosong University, 2Department of Rehabilitation, The Graduate School of Health and Welfare, Woosong University, Daejeon, 3Hwirim Korean Medicine Hospital, Busan, 4Rehabilitation Center, Bomunsan Ecologic Nursing Hospital, 5Rehabilitation Center, Teunteun Convalescent Hospital, Daejeon, Korea

Correspondence to: Heesu Kim
E-mail: heesukimpt@gmail.com
https://orcid.org/0000-0002-1684-5636

Received: February 1, 2023; Revised: February 6, 2023; Accepted: February 6, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background: Equating is a statistical procedure used to create a common measurement scale across two instruments. Item-level information should be taken into consideration so that scores can communicate interchangeably across the instruments. Objects: To investigate a common measurement scale across two health-related quality of life questionnaires (HRQOL) applied to various cancer survivors who underwent palliative care in healthcare institutions.
Methods: A total of 139 cancer survivors who underwent palliative care were recruited from two rehabilitation hospitals and an oriental medicine hospital. Participants consisted of various cancer survivors who presented to the sites for palliative care. They were asked to fill out Korean versions of the World Health Organization Quality of Life (WHOQOL-BREF) and EuroQOL-5 dimension (EQ-5D) questionnaires following the palliative care. For the item level comparison, the Rasch rating scale model was used to investigate how participants regarded individual test items of two instruments in relation to item difficulty calibrations.
Results: All items except the three items fit the Rasch model. One item (anxiety/depression) of the EQ-5D and two items (dependence on medical aids and negative feelings) of the WHOQOL- BREF are misfit. The WHOQOL-BREF targets the survivors well, while the EQ-5D is able to target the survivors with lower HRQOL levels with some ceiling effects. By inspecting the item difficulty calibrations of the two instruments, five items of the WHOQOL-BREF are selected as common items in relation to the EQ-5D. These five items are considered compatible with each other. Differential item functioning (DIF) analysis reveals that the healthcare item of the WHOQOL-BREF vs the self-care item of the EQ-5D exhibits significant DIF.
Conclusion: Findings suggest that one paired item should be taken into consideration when equating the WHOQOL-BREF and the EQ-5D applied to cancer survivors who underwent palliative care.

Keywords: Cancer survivors, Outcome assessment, Palliative care, Psychometrics, Quality of life

Article

Original Article

Phys. Ther. Korea 2023; 30(1): 32-40

Published online February 20, 2023 https://doi.org/10.12674/ptk.2023.30.1.32

Copyright © Korean Research Society of Physical Therapy.

Equating Two Health-related Quality of Life Instruments Applied to Cancer Survivors Who Underwent Palliative Care

Bongsam Choi1 , PT, MPH, PhD, Heesu Kim2 , PT, BS, Sunhwi Bang3 , KMD, Byunggwan Kim4 , PT, Jaekwang Shim5 , PT, PhD

1Department of Physical Therapy, College of Health and Welfare, Woosong University, 2Department of Rehabilitation, The Graduate School of Health and Welfare, Woosong University, Daejeon, 3Hwirim Korean Medicine Hospital, Busan, 4Rehabilitation Center, Bomunsan Ecologic Nursing Hospital, 5Rehabilitation Center, Teunteun Convalescent Hospital, Daejeon, Korea

Correspondence to:Heesu Kim
E-mail: heesukimpt@gmail.com
https://orcid.org/0000-0002-1684-5636

Received: February 1, 2023; Revised: February 6, 2023; Accepted: February 6, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background: Equating is a statistical procedure used to create a common measurement scale across two instruments. Item-level information should be taken into consideration so that scores can communicate interchangeably across the instruments. Objects: To investigate a common measurement scale across two health-related quality of life questionnaires (HRQOL) applied to various cancer survivors who underwent palliative care in healthcare institutions.
Methods: A total of 139 cancer survivors who underwent palliative care were recruited from two rehabilitation hospitals and an oriental medicine hospital. Participants consisted of various cancer survivors who presented to the sites for palliative care. They were asked to fill out Korean versions of the World Health Organization Quality of Life (WHOQOL-BREF) and EuroQOL-5 dimension (EQ-5D) questionnaires following the palliative care. For the item level comparison, the Rasch rating scale model was used to investigate how participants regarded individual test items of two instruments in relation to item difficulty calibrations.
Results: All items except the three items fit the Rasch model. One item (anxiety/depression) of the EQ-5D and two items (dependence on medical aids and negative feelings) of the WHOQOL- BREF are misfit. The WHOQOL-BREF targets the survivors well, while the EQ-5D is able to target the survivors with lower HRQOL levels with some ceiling effects. By inspecting the item difficulty calibrations of the two instruments, five items of the WHOQOL-BREF are selected as common items in relation to the EQ-5D. These five items are considered compatible with each other. Differential item functioning (DIF) analysis reveals that the healthcare item of the WHOQOL-BREF vs the self-care item of the EQ-5D exhibits significant DIF.
Conclusion: Findings suggest that one paired item should be taken into consideration when equating the WHOQOL-BREF and the EQ-5D applied to cancer survivors who underwent palliative care.

Keywords: Cancer survivors, Outcome assessment, Palliative care, Psychometrics, Quality of life

Fig 1.

Figure 1.Item-person map of the EQ-5D and the WHOQOL-BREF. The graph shows person ability measures (left) and item difficulty measures (right) with the 0–100 converted score following the Rasch analysis. WHOQOL-BREF, World Health Organization Quality of Life; EQ-5D, EuroQOL-5 dimension.
Physical Therapy Korea 2023; 30: 32-40https://doi.org/10.12674/ptk.2023.30.1.32

Fig 2.

Figure 2.Item-person map of the EQ-5D (left) versus the five items of the WHOQOL-BREF (right). The graph represents item difficulty measures on the right side of each map with 0–100 converted score and the person ability measures on the left side following the Rasch analysis. Each analysis is anchored on the average item difficulty measure to 50 for comparisons. The ‘M’ represents the average item calibrations for both instruments. WHOQOL-BREF, World Health Organization Quality of Life; EQ-5D, EuroQOL-5 dimension.
Physical Therapy Korea 2023; 30: 32-40https://doi.org/10.12674/ptk.2023.30.1.32

Fig 3.

Figure 3.DIF plots for the EQ-5D items versus the five items of the WHOQOL-BREF. The dashed lines connecting the filled dots represent the upper and lower 95% confidence intervals. The measures were converted to 0–100 score from logits following the Rasch analysis. DIF, differential item functioning; WHOQOL-BREF, World Health Organization Quality of Life; EQ-5D, EuroQOL-5 dimension.
Physical Therapy Korea 2023; 30: 32-40https://doi.org/10.12674/ptk.2023.30.1.32

Table 1 . Fit statistics of the EQ-5D in descending order of difficulty.

EQ-5DDifficultyInfit MnSqInfit ZSTDOutfit MnSqOutfit ZSTD
EQ-5D 4 pain/discomfort52.940.84–1.20.85–1.1
EQ-5D 3 usual activities51.330.74–2.20.64–2.9
EQ-5D 1 mobility44.250.97–0.11.120.6
EQ-5D 5 anxiety/depression43.371.664.11.533.5
EQ-5D 2 self-care32.870.64–2.00.46–1.8

EQ-5D, EuroQOL-5 dimension; MnSq, mean square standardized residuals; ZSTD, Z score standardized..


Table 2 . Fit statistics of the WHOQOL-BREF in descending order of difficulty.

WHOQOLDifficultyInfit MnSqInfit ZSTDOutfit MnSqOutfit ZSTD
WHOQOL 4 Dependence of medical aids53.391.594.71.896.4
WHOQOL 21 Sexual activity53.200.98–0.11.030.3
WHOQOL 18 Work capacity51.740.88–1.10.84–1.4
WHOQOL 14 Leisure activity51.541.100.91.080.7
WHOQOL 12 Financial support50.491.080.71.131.0
WHOQOL 16 Sleep and rest50.091.302.61.433.4
WHOQOL 11 Bodily image49.310.93–0.60.93–0.6
WHOQOL 5 Positive feeling48.800.86–1.31.030.3
WHOQOL 10 Energy for daily life48.770.82–1.60.80–1.6
WHOQOL 13 Accessibility of information48.080.96–0.30.95–0.4
WHOQOL 17 Activities of daily living47.680.70–3.00.73–2.6
WHOQOL 8 Security47.160.82–1.50.81–1.5
WHOQOL 23 Home environment46.961.020.21.050.5
WHOQOL 19 Self-esteem46.880.70–2.80.70–2.8
WHOQOL 15 Mobility45.930.87–1.20.84–1.3
WHOQOL 9 Physical environment45.840.92–0.60.90–0.7
WHOQOL 22 Social support44.021.161.31.161.2
WHOQOL 7 Concentration43.511.070.61.060.5
WHOQOL 3 Pain43.391.221.81.412.7
WHOQOL 20 Personal relationship42.220.81–1.60.81–1.6
WHOQOL 6 Personal belief41.901.090.81.070.5
WHOQOL 26 Negative feeling40.471.302.11.563.3
WHOQOL 24 Health care39.630.95–0.30.93–0.5
WHOQOL 25 Transport39.060.88–0.90.88–0.9

WHOQOL-BREF, World Health Organization Quality of Life; MnSq, mean square standardized residuals; ZSTD, Z score standardized..


Table 3 . Item difficulty of the WHOQOL-BREF in descending order of difficulty.

ItemDifficulty (logits)Difficulty (logits)Item
EQ-5D 452.9458.52WHOQOL 18
EQ-5D 351.3356.99WHOQOL 12
EQ-5D 144.2549.82WHOQOL 9
EQ-5D 543.3745.08WHOQOL 3
EQ-5D 232.8739.59WHOQOL 24

WHOQOL-BREF, World Health Organization Quality of Life; EQ-5D, EuroQOL-5 dimension..