Arthritis Care & Research DOI 10.1002/acr.22448
Original Article
Validation of the LupusPRO in Hong Kong Chinese patients with systemic lupus erythematosus 1
Chi Chiu Mok, 2Mark Kosinski, 1Ling Yin Ho, 1Kar Li Chan, 2Meenakshi Jolly 1 Department of Medicine, Tuen Mun Hospital, Hong Kong, China and 2Rush University Medical Center, Chicago, Il, USA Correspondence to:
Dr. Chi Chiu Mok (MD, FRCP) Department of Medicine Tuen Mun Hospital Tsing Chung Koon Road New Territories Hong Kong, SAR China
Tel: (852) 2468 5386 Fax: (852) 2456 9100 Email: [email protected]
Other authors Mark Kosinski (MA) QualityMetric Incorporated Lincoln, RI Ling Yin HO (MB, FRCP) Associate consultant in Rheumatology Tuen Mun Hospital Ka Li CHAN (MB, FRCP) Rheumatology registrar Tuen Mun Hospital Meenakshi Jolly (MD, MS) Associate Professor in Medicine Rush University Medical Center
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as an ‘Accepted Article’, doi: 10.1002/acr.22448 © 2014 American College of Rheumatology Received: Mar 24, 2014; Revised: Jul 07, 2014; Accepted: Aug 12, 2014
Arthritis Care & Research
Page 2 of 30
Abstract Background: LupusPRO is a disease-targeted patient reported outcome measure that was developed and validated for assessment of quality of life in US patients with systemic lupus erythematosus (SLE).
We hereby present results of adaptating the LupusPRO into Chinese
and testing its psychometric properties in Chinese patients with SLE. Methods: LupusPRO was translated into “Traditional” Chinese, followed by pretesting among native Cantonese Chinese speakers. The translation version was revised based on the feedback obtained.
The Chinese language LupusPRO tool was administered along with the
generic Patient Reported Outcomes tool (SF36) to ethnic Chinese SLE patients.
At the same
time, demographic, clinical data, disease activity (SELENA-SLEDAI) and damage (SLICC-ACR/SDI) were obtained.
We performed confirmatory factor analysis of the
Chinese LupusPRO and evaluated internal consistency reliability, convergent and criterion validity. Results: Among the 463 SLE patients (95% women) with a mean (SD) age of 42.3 (13.5) years, mean PGA score was 0.48 (SD=0.45), mean SELENA-SLEDAI was 2.9 (SD=3.0) and mean SDI was 0.7 (SD=1.2).
Results of factor analysis conformed to the original LupusPRO
model, with only minor modifications. The reliability of the LupusPRO domains ranged from 0.60-0.94. LupusPRO domains had correlations as expected with the corresponding SF36 domains. Significant but weak correlation with disease activity was noted for criterion
2
John Wiley & Sons, Inc.
Page 3 of 30
Arthritis Care & Research
validity as expected. Conclusions: Chinese language LupusPRO has fair psychometric properties, and may be used in SLE clinical trials. Keywords: Lupus, quality of life, Chinese, patient-reported outcome, ethnic Short running title: Validation of LupusPRO in Hong Kong Chinese
3
John Wiley & Sons, Inc.
Arthritis Care & Research
Significance and Innovation 1.
The LupusPRO is a disease-targeted patient reported outcome measure that has been validated for assessment of quality of life in US patients with SLE
2.
This study validates the Chinese language LupusPRO in a large cohort of southern Chinese patients with SLE
3.
The Chinese LupusPRO has fair psychometric properties and can be used for clinical trials
4
John Wiley & Sons, Inc.
Page 4 of 30
Page 5 of 30
Arthritis Care & Research
Introduction Systemic lupus erythematosus (SLE) is a chronic multi-systemic autoimmune disease that mainly affects women of the reproductive age.
The disease course is unpredictable and
interspersed with periods of exacerbations and remissions (1).
Although the prognosis of the
disease has improved tremendously in the past few decades, further improvement is hindered by many factors that include refractory manifestations and toxicities related to conventional therapies (2).
Because of symptoms related to disease activity, treatment-related
complications, or accrued damage, the quality of life of patients with SLE is significantly impaired.
A number of studies in different ethnic groups have reported poorer quality of life
in patients with SLE when compared to healthy subjects (3-5).
In a previous longitudinal
study involving 155 Chinese SLE patients, we showed that the health-related quality of life (HRQOL) was significantly impaired when compared to controls and adjusting for age, sex, education and poverty (6).
Pre-existing organ damage was associated with poorer HRQOL
and new damage over 2 years predicted further decline in HRQOL.
In another study, it was
shown that the quality of life of SLE patients was worse than some other common chronic diseases (7). The Medical Outcomes Study Short Form-36 (SF-36) has been the most commonly utilized patient reported outcome (PRO) tool in longitudinal observational studies and randomized controlled therapeutic trials of SLE (8-10).
It is well validated but not specific
5
John Wiley & Sons, Inc.
Arthritis Care & Research
to SLE.
Page 6 of 30
Disease specific questionnaires have been developed with the intention of
enhancing the responsiveness and content validity for SLE compared to generic instruments. The LupusPRO is a disease-targeted PRO measure that was developed and validated in US from SLE patients (11).
Unlike other lupus-specific questionnaires such as the UK
LupusQoL (12), it consists of both health-related (8 domains) and non-health-related (4 domains) domains to enable an understanding of the broader burden of the disease.
The
LupusPRO has been cross culturally adapted and validated in various countries (Canada, Philippines) and different languages such as Turkish, Spanish, French and Filipino (13-16). However, it has not been validated in Chinese. We hereby report results of cross-cultural adaptation of LupusPRO into Chinese language, and testing of its psychometric properties among Chinese patients with SLE.
6
John Wiley & Sons, Inc.
Page 7 of 30
Arthritis Care & Research
Patients and methods Study population and data collection Consecutive SLE patients who attended the rheumatology out-patient clinics or were admitted to the medical wards of Tuen Mun Hospital, Hong Kong, China between February and June 2013 were recruited.
All patients were ethnic Chinese with their family origin in
the southern part of China and fulfilled at least 4 of the 1997 American College of Rheumatology classification criteria for SLE (17). the participants.
Written consent was obtained from all
The study was approved by the Ethics Committee of Tuen Mun Hospital,
Hong Kong. Participants were asked to complete the LupusPRO questionnaire along with the generic PRO tool SF36.
Demographic and clinical data (clinical manifestations, autoantibodies and
medications within one month of study) were obtained.
SLE disease activity at the time of
questionnaire completion was assessed by the Safety of Estrogens in Lupus Erythematosus National Assessment-SLE Disease Activity Index (SELENA-SLEDAI) and organ damage was assessed by the SLICC-ACR Damage Index (SDI). LupusPRO The LupusPRO has 2 constructs: HRQOL and non-HRQOL.
The HRQOL domains are
SLE symptoms, cognition, SLE medications, physical health (physical function and role physical), pain-vitality (fatigue, sleep), body image, emotional health (emotional function and
7
John Wiley & Sons, Inc.
Arthritis Care & Research
Page 8 of 30
role emotional), and procreation (sexual health and reproduction).
The non-HRQOL
domains are desires/goals, relationship/social support, coping, and satisfaction with medical care.
LupusPRO has 43 items (30 for HRQOL construct, 13 for non-HRQOL construct) and
a 4 weeks recall period. of the time.”
Each item has five options ranging from “none of the time” to “all
The survey completion time ranges between 5 to 7 minutes.
Each domain
scores, total HRQOL, and total non-HRQOL scores range from 0 to 100, where higher score denotes better QOL.
The tool has excellent psychometric properties in US patients (11).
Translation The 43 item English LupusPRO was translated by certified translation company using standard guidelines (18) into “Traditional” Chinese using forwards and backwards translation methods.
Two translators of each language were involved in the process of forwards and
backwards translations.
The backward translation (English version) was reviewed by the
last author (MJ), the tool developer, to confirm that the concepts of the LupusPRO items, responses, instructions and the overall tool remained the same.
Feedback was provided to
the translation company, and appropriate changes made when needed to maintain the integrity of the original tool in the translated version.
The finalized version was also reviewed
carefully by the first author, a native Chinese (Cantonese) language speaker, and minor changes made to retain the “Traditional” Chinese language form throughout the survey. translated tool was pretested among five native Cantonese Chinese speakers.
8
John Wiley & Sons, Inc.
The
Based on the
Page 9 of 30
Arthritis Care & Research
feedback obtained, the translated tool was revised until no issues on feedback from pretesting were noted.
The finalized tool was then administered to 463 patients with SLE.
Psychometric properties COnsensus-based Standards for the selection of health Measurement Instrument (COSMIN) distinguish three quality domains: Reliability, validity and responsiveness (19). The psychometric properties studied in this paper included reliability and validity. Reliability indicates the degree to which the measurement is free from measurement error. Internal consistency reliability (ICR) reflects the degree of interrelatedness among the items of the same domain. to measure.
Validity is the degree to which the measure reflects what it is supposed
Construct validity refers to the degree to which the scores of the instrument are
consistent with the hypotheses (e.g. with regard to internal relationships, relationships to scores of other instruments, or differences between relevant groups).
Hypotheses regarding
internal relationships are often tested using confirmatory factor analysis (CFA).
Analyses
regarding external relationships encompass analyses of convergent, discriminant, criterion, and known-groups validity.
Convergent validity is present if the new instrument scores
correlate with other measures of the same construct. correlation with unrelated constructs.
Discriminant validity requires lack of
Criterion validity refers to the correlation between the
new instrument and an external “objective” reference. Known-groups validity is determined by the ability of the instrument to differentiate between groups that are known to vary in
9
John Wiley & Sons, Inc.
Arthritis Care & Research
Page 10 of 30
characteristic e.g. disease activity. Assessment of SLE activity and damage Disease activity of SLE was assessed by the SELENA-SLEDAI, a validated instrument that was employed in the SELENA trials (20). SELENA-SLEDAI includes the physician’s global assessment (PGA) of disease activity (score 0-3).
The PGA and the total SLEDAI
score was used in this study. Organ damage was assessed by the SLICC/ACR Damage Index (SDI) (21).
Damage
(after SLE diagnosis) has to be present for >6 months before it is scored, irrespective of the cause and be irreversible. Statistical analyses The conceptual framework (hypothesized item to scale relationships) of the LupusPRO was evaluated using CFA appropriate for categorical data. CFA was conducted with the LupusPRO item responses using a robust weighted least squares estimator.
Items were
considered to have strong loading if the item factor loading was ≥0.50. The goodness of fit of the hypothesized item to scale relationships was evaluated with the Comparative Fit Index (CFI) and the Root Mean Square Error of Approximation (RMSEA).
The CFI is a
comparative fit index, which quantify the amount of difference between the examined model and the independence model, while the RMSEA quantify the difference to the fully saturated model. General recommendations are that acceptable fit requires CFA ≥ 0.95 (22-23) and
10
John Wiley & Sons, Inc.
Page 11 of 30
Arthritis Care & Research
RMSEA ≤ 0.08. The ICR for each domain was evaluated using Cronbach’s alpha.
In some cases, the
CFA revealed correlated residuals (local item dependence (24-25)) which may inflate ICR. We adjusted for local dependence in ICR analyses by forming testlets for the locally dependent items (25). We hypothesized a moderate correlation between corresponding domains (Physical Health, Emotional Health, Fatigue-Pain) of the LupusPRO and SF-36 (Physical function, role physical, mental health, role emotional, bodily pain and vitality) to establish convergent validity.
Correlation between corresponding LupusPRO and SF-36 domains was assessed
using Spearman’s correlation coefficient for convergent validity.
Discriminant validity of
LupusPRO domains using correlational analysis against non-related domains of the SF-36 were assessed.
Criterion validity for the Lupus Symptoms domain was performed against
disease activity assessments (SELENA-SLEDAI, PGA). Criterion validity was judged using correlation between LupusPRO domains and physician based measures of disease activity and damage (SELENA-SLEDAI descriptors and total scores, SDI total scores).
Weak correlation between LupusPRO and SLE disease
activity was hypothesized due to a priori and unique PRO information captured by the tool. Correlations were classified as strong (r ≥ 0.5), moderate (0.3 ≤ r < 0.5), weak (0.1 ≤ r < 0.3), or absent (r < 0.1).
Known group validity was judged against patient reported health
11
John Wiley & Sons, Inc.
Arthritis Care & Research
Page 12 of 30
status (SF-36 item 1) and disease status (SELENA-SLEDAI, SDI).
Analysis of variance
(ANOVA), with assumption of unequal variance between groups, was used to compare LupusPRO domain scores stratified by ‘’known groups’’. tailed.
12
John Wiley & Sons, Inc.
All reported p values are two
Page 13 of 30
Arthritis Care & Research
Results Four hundred and sixty-three Chinese patients with SLE were studied (95% women). The mean (SD) age of the patients was 42.3 (13.5) years and the mean (SD) SLE duration was 9.9 (7.5) years.
Table 1 shows the cumulative clinical manifestations of the patients studied.
At the time of questionnaire completion, the mean PGA score was 0.48 (SD=0.45) and the median score was 0.3 (IQR=0.4). The mean SELENA-SLEDAI score was 2.9 (SD=3.0), median 2.0 (IQR=4.0). The mean SDI score was 0.7 (SD=1.2), the median was 0.0 (IQR=1.0). Seventy-seven (16.6 %) patients had SELENA-SLEDAI greater than 4, while 183 (39.5%) had SDI of one or greater. Sixty percent of the patients were on prednisolone and 64% patients were receiving hydroxychloroquine (Table 1). Summary LupusPRO and SF36 domain scores are shown in Table 2, along with floor and ceiling effects for both the tools. To obtain satisfactory model fit in the CFA (CFI =0.955; RMSEA=0.080), two minor model modifications were necessary: specification of residual correlations between item 5 and 6 in the emotional health scale, and between item 2 and 3 in the Desires-Goals scale (Table 3). The model fit statistics on CFA (Table 4) were in the acceptable range (CFI >0.90; TLI>0.90; RMSEA
Original Article
Validation of the LupusPRO in Hong Kong Chinese patients with systemic lupus erythematosus 1
Chi Chiu Mok, 2Mark Kosinski, 1Ling Yin Ho, 1Kar Li Chan, 2Meenakshi Jolly 1 Department of Medicine, Tuen Mun Hospital, Hong Kong, China and 2Rush University Medical Center, Chicago, Il, USA Correspondence to:
Dr. Chi Chiu Mok (MD, FRCP) Department of Medicine Tuen Mun Hospital Tsing Chung Koon Road New Territories Hong Kong, SAR China
Tel: (852) 2468 5386 Fax: (852) 2456 9100 Email: [email protected]
Other authors Mark Kosinski (MA) QualityMetric Incorporated Lincoln, RI Ling Yin HO (MB, FRCP) Associate consultant in Rheumatology Tuen Mun Hospital Ka Li CHAN (MB, FRCP) Rheumatology registrar Tuen Mun Hospital Meenakshi Jolly (MD, MS) Associate Professor in Medicine Rush University Medical Center
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as an ‘Accepted Article’, doi: 10.1002/acr.22448 © 2014 American College of Rheumatology Received: Mar 24, 2014; Revised: Jul 07, 2014; Accepted: Aug 12, 2014
Arthritis Care & Research
Page 2 of 30
Abstract Background: LupusPRO is a disease-targeted patient reported outcome measure that was developed and validated for assessment of quality of life in US patients with systemic lupus erythematosus (SLE).
We hereby present results of adaptating the LupusPRO into Chinese
and testing its psychometric properties in Chinese patients with SLE. Methods: LupusPRO was translated into “Traditional” Chinese, followed by pretesting among native Cantonese Chinese speakers. The translation version was revised based on the feedback obtained.
The Chinese language LupusPRO tool was administered along with the
generic Patient Reported Outcomes tool (SF36) to ethnic Chinese SLE patients.
At the same
time, demographic, clinical data, disease activity (SELENA-SLEDAI) and damage (SLICC-ACR/SDI) were obtained.
We performed confirmatory factor analysis of the
Chinese LupusPRO and evaluated internal consistency reliability, convergent and criterion validity. Results: Among the 463 SLE patients (95% women) with a mean (SD) age of 42.3 (13.5) years, mean PGA score was 0.48 (SD=0.45), mean SELENA-SLEDAI was 2.9 (SD=3.0) and mean SDI was 0.7 (SD=1.2).
Results of factor analysis conformed to the original LupusPRO
model, with only minor modifications. The reliability of the LupusPRO domains ranged from 0.60-0.94. LupusPRO domains had correlations as expected with the corresponding SF36 domains. Significant but weak correlation with disease activity was noted for criterion
2
John Wiley & Sons, Inc.
Page 3 of 30
Arthritis Care & Research
validity as expected. Conclusions: Chinese language LupusPRO has fair psychometric properties, and may be used in SLE clinical trials. Keywords: Lupus, quality of life, Chinese, patient-reported outcome, ethnic Short running title: Validation of LupusPRO in Hong Kong Chinese
3
John Wiley & Sons, Inc.
Arthritis Care & Research
Significance and Innovation 1.
The LupusPRO is a disease-targeted patient reported outcome measure that has been validated for assessment of quality of life in US patients with SLE
2.
This study validates the Chinese language LupusPRO in a large cohort of southern Chinese patients with SLE
3.
The Chinese LupusPRO has fair psychometric properties and can be used for clinical trials
4
John Wiley & Sons, Inc.
Page 4 of 30
Page 5 of 30
Arthritis Care & Research
Introduction Systemic lupus erythematosus (SLE) is a chronic multi-systemic autoimmune disease that mainly affects women of the reproductive age.
The disease course is unpredictable and
interspersed with periods of exacerbations and remissions (1).
Although the prognosis of the
disease has improved tremendously in the past few decades, further improvement is hindered by many factors that include refractory manifestations and toxicities related to conventional therapies (2).
Because of symptoms related to disease activity, treatment-related
complications, or accrued damage, the quality of life of patients with SLE is significantly impaired.
A number of studies in different ethnic groups have reported poorer quality of life
in patients with SLE when compared to healthy subjects (3-5).
In a previous longitudinal
study involving 155 Chinese SLE patients, we showed that the health-related quality of life (HRQOL) was significantly impaired when compared to controls and adjusting for age, sex, education and poverty (6).
Pre-existing organ damage was associated with poorer HRQOL
and new damage over 2 years predicted further decline in HRQOL.
In another study, it was
shown that the quality of life of SLE patients was worse than some other common chronic diseases (7). The Medical Outcomes Study Short Form-36 (SF-36) has been the most commonly utilized patient reported outcome (PRO) tool in longitudinal observational studies and randomized controlled therapeutic trials of SLE (8-10).
It is well validated but not specific
5
John Wiley & Sons, Inc.
Arthritis Care & Research
to SLE.
Page 6 of 30
Disease specific questionnaires have been developed with the intention of
enhancing the responsiveness and content validity for SLE compared to generic instruments. The LupusPRO is a disease-targeted PRO measure that was developed and validated in US from SLE patients (11).
Unlike other lupus-specific questionnaires such as the UK
LupusQoL (12), it consists of both health-related (8 domains) and non-health-related (4 domains) domains to enable an understanding of the broader burden of the disease.
The
LupusPRO has been cross culturally adapted and validated in various countries (Canada, Philippines) and different languages such as Turkish, Spanish, French and Filipino (13-16). However, it has not been validated in Chinese. We hereby report results of cross-cultural adaptation of LupusPRO into Chinese language, and testing of its psychometric properties among Chinese patients with SLE.
6
John Wiley & Sons, Inc.
Page 7 of 30
Arthritis Care & Research
Patients and methods Study population and data collection Consecutive SLE patients who attended the rheumatology out-patient clinics or were admitted to the medical wards of Tuen Mun Hospital, Hong Kong, China between February and June 2013 were recruited.
All patients were ethnic Chinese with their family origin in
the southern part of China and fulfilled at least 4 of the 1997 American College of Rheumatology classification criteria for SLE (17). the participants.
Written consent was obtained from all
The study was approved by the Ethics Committee of Tuen Mun Hospital,
Hong Kong. Participants were asked to complete the LupusPRO questionnaire along with the generic PRO tool SF36.
Demographic and clinical data (clinical manifestations, autoantibodies and
medications within one month of study) were obtained.
SLE disease activity at the time of
questionnaire completion was assessed by the Safety of Estrogens in Lupus Erythematosus National Assessment-SLE Disease Activity Index (SELENA-SLEDAI) and organ damage was assessed by the SLICC-ACR Damage Index (SDI). LupusPRO The LupusPRO has 2 constructs: HRQOL and non-HRQOL.
The HRQOL domains are
SLE symptoms, cognition, SLE medications, physical health (physical function and role physical), pain-vitality (fatigue, sleep), body image, emotional health (emotional function and
7
John Wiley & Sons, Inc.
Arthritis Care & Research
Page 8 of 30
role emotional), and procreation (sexual health and reproduction).
The non-HRQOL
domains are desires/goals, relationship/social support, coping, and satisfaction with medical care.
LupusPRO has 43 items (30 for HRQOL construct, 13 for non-HRQOL construct) and
a 4 weeks recall period. of the time.”
Each item has five options ranging from “none of the time” to “all
The survey completion time ranges between 5 to 7 minutes.
Each domain
scores, total HRQOL, and total non-HRQOL scores range from 0 to 100, where higher score denotes better QOL.
The tool has excellent psychometric properties in US patients (11).
Translation The 43 item English LupusPRO was translated by certified translation company using standard guidelines (18) into “Traditional” Chinese using forwards and backwards translation methods.
Two translators of each language were involved in the process of forwards and
backwards translations.
The backward translation (English version) was reviewed by the
last author (MJ), the tool developer, to confirm that the concepts of the LupusPRO items, responses, instructions and the overall tool remained the same.
Feedback was provided to
the translation company, and appropriate changes made when needed to maintain the integrity of the original tool in the translated version.
The finalized version was also reviewed
carefully by the first author, a native Chinese (Cantonese) language speaker, and minor changes made to retain the “Traditional” Chinese language form throughout the survey. translated tool was pretested among five native Cantonese Chinese speakers.
8
John Wiley & Sons, Inc.
The
Based on the
Page 9 of 30
Arthritis Care & Research
feedback obtained, the translated tool was revised until no issues on feedback from pretesting were noted.
The finalized tool was then administered to 463 patients with SLE.
Psychometric properties COnsensus-based Standards for the selection of health Measurement Instrument (COSMIN) distinguish three quality domains: Reliability, validity and responsiveness (19). The psychometric properties studied in this paper included reliability and validity. Reliability indicates the degree to which the measurement is free from measurement error. Internal consistency reliability (ICR) reflects the degree of interrelatedness among the items of the same domain. to measure.
Validity is the degree to which the measure reflects what it is supposed
Construct validity refers to the degree to which the scores of the instrument are
consistent with the hypotheses (e.g. with regard to internal relationships, relationships to scores of other instruments, or differences between relevant groups).
Hypotheses regarding
internal relationships are often tested using confirmatory factor analysis (CFA).
Analyses
regarding external relationships encompass analyses of convergent, discriminant, criterion, and known-groups validity.
Convergent validity is present if the new instrument scores
correlate with other measures of the same construct. correlation with unrelated constructs.
Discriminant validity requires lack of
Criterion validity refers to the correlation between the
new instrument and an external “objective” reference. Known-groups validity is determined by the ability of the instrument to differentiate between groups that are known to vary in
9
John Wiley & Sons, Inc.
Arthritis Care & Research
Page 10 of 30
characteristic e.g. disease activity. Assessment of SLE activity and damage Disease activity of SLE was assessed by the SELENA-SLEDAI, a validated instrument that was employed in the SELENA trials (20). SELENA-SLEDAI includes the physician’s global assessment (PGA) of disease activity (score 0-3).
The PGA and the total SLEDAI
score was used in this study. Organ damage was assessed by the SLICC/ACR Damage Index (SDI) (21).
Damage
(after SLE diagnosis) has to be present for >6 months before it is scored, irrespective of the cause and be irreversible. Statistical analyses The conceptual framework (hypothesized item to scale relationships) of the LupusPRO was evaluated using CFA appropriate for categorical data. CFA was conducted with the LupusPRO item responses using a robust weighted least squares estimator.
Items were
considered to have strong loading if the item factor loading was ≥0.50. The goodness of fit of the hypothesized item to scale relationships was evaluated with the Comparative Fit Index (CFI) and the Root Mean Square Error of Approximation (RMSEA).
The CFI is a
comparative fit index, which quantify the amount of difference between the examined model and the independence model, while the RMSEA quantify the difference to the fully saturated model. General recommendations are that acceptable fit requires CFA ≥ 0.95 (22-23) and
10
John Wiley & Sons, Inc.
Page 11 of 30
Arthritis Care & Research
RMSEA ≤ 0.08. The ICR for each domain was evaluated using Cronbach’s alpha.
In some cases, the
CFA revealed correlated residuals (local item dependence (24-25)) which may inflate ICR. We adjusted for local dependence in ICR analyses by forming testlets for the locally dependent items (25). We hypothesized a moderate correlation between corresponding domains (Physical Health, Emotional Health, Fatigue-Pain) of the LupusPRO and SF-36 (Physical function, role physical, mental health, role emotional, bodily pain and vitality) to establish convergent validity.
Correlation between corresponding LupusPRO and SF-36 domains was assessed
using Spearman’s correlation coefficient for convergent validity.
Discriminant validity of
LupusPRO domains using correlational analysis against non-related domains of the SF-36 were assessed.
Criterion validity for the Lupus Symptoms domain was performed against
disease activity assessments (SELENA-SLEDAI, PGA). Criterion validity was judged using correlation between LupusPRO domains and physician based measures of disease activity and damage (SELENA-SLEDAI descriptors and total scores, SDI total scores).
Weak correlation between LupusPRO and SLE disease
activity was hypothesized due to a priori and unique PRO information captured by the tool. Correlations were classified as strong (r ≥ 0.5), moderate (0.3 ≤ r < 0.5), weak (0.1 ≤ r < 0.3), or absent (r < 0.1).
Known group validity was judged against patient reported health
11
John Wiley & Sons, Inc.
Arthritis Care & Research
Page 12 of 30
status (SF-36 item 1) and disease status (SELENA-SLEDAI, SDI).
Analysis of variance
(ANOVA), with assumption of unequal variance between groups, was used to compare LupusPRO domain scores stratified by ‘’known groups’’. tailed.
12
John Wiley & Sons, Inc.
All reported p values are two
Page 13 of 30
Arthritis Care & Research
Results Four hundred and sixty-three Chinese patients with SLE were studied (95% women). The mean (SD) age of the patients was 42.3 (13.5) years and the mean (SD) SLE duration was 9.9 (7.5) years.
Table 1 shows the cumulative clinical manifestations of the patients studied.
At the time of questionnaire completion, the mean PGA score was 0.48 (SD=0.45) and the median score was 0.3 (IQR=0.4). The mean SELENA-SLEDAI score was 2.9 (SD=3.0), median 2.0 (IQR=4.0). The mean SDI score was 0.7 (SD=1.2), the median was 0.0 (IQR=1.0). Seventy-seven (16.6 %) patients had SELENA-SLEDAI greater than 4, while 183 (39.5%) had SDI of one or greater. Sixty percent of the patients were on prednisolone and 64% patients were receiving hydroxychloroquine (Table 1). Summary LupusPRO and SF36 domain scores are shown in Table 2, along with floor and ceiling effects for both the tools. To obtain satisfactory model fit in the CFA (CFI =0.955; RMSEA=0.080), two minor model modifications were necessary: specification of residual correlations between item 5 and 6 in the emotional health scale, and between item 2 and 3 in the Desires-Goals scale (Table 3). The model fit statistics on CFA (Table 4) were in the acceptable range (CFI >0.90; TLI>0.90; RMSEA
