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Abstract Number: 1667

Confirmatory Factor Analysis of the Patient-Reported Perceived Deficits Questionnaire in Systemic Lupus Erythematosus: Cautions for Use of Subscales

Lisa Engel1, Jiandong Su1, Emily Nalder2, Yael Goverover3, Monique Gignac4, Carmela Tartaglia5, Nicole Anderson1 and Zahi Touma1, 1University of Toronto, Toronto Western Hospital, Toronto, ON, Canada, 2Department of Occupational Science and Occupational Therapy, University of Toronto, Toronto, ON, Canada, 3Department of Occupational Therapy, New York University, New York, NY, 4Instititue for Work and Health, Toronto, ON, Canada, 5University of Toronto, Krembil Neurosciences Centre, Toronto, ON, Canada

Meeting: 2018 ACR/ARHP Annual Meeting

Keywords: activities of daily living (ADL), Cognitive dysfunction, Outcome measures, patient-reported outcome measures and systemic lupus erythematosus (SLE)

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Session Information

Date: Monday, October 22, 2018

Session Title: Systemic Lupus Erythematosus – Clinical Poster II: Biomarkers and Outcomes

Session Type: ACR Poster Session B

Session Time: 9:00AM-11:00AM

Background/Purpose:  Approximately 38% of adults living with Systemic Lupus Erythematosus (SLE) experience cognitive impairment (CI) that can detrimentally affect employment, disease self-management, and quality of life. Identifying those with SLE related CI is critical, but is difficult to do in busy and resource-limited clinics. The patient-reported 20-item Perceived Deficits Questionnaire (PDQ-20), used to screen for SLE related CI, could be less time and cost-burdensome than other objective instruments. However, there is a dearth of published measurement property evidence for using the PDQ-20 with SLE patients. In adults with Multiple Sclerosis the PDQ-20 is purported to have four factors (subscales): attention/concentration, retrospective memory, prospective memory, and planning/organization. This structure has not been examined in adults with SLE.  The purpose of this study is to examine the factor structure and the internal consistency of the PDQ-20 in an SLE cohort.

Methods: Consecutive SLE patients aged 18-65 years were recruited from a single rheumatology center between July 2016 and March 2018. Patients completed the PDQ-20.  Analyses included socio-demographic descriptive analyses and confirmatory factor analyses (CFA) of the purported PDQ-20 four-factor structure. Sample size calculations indicated that a cohort of n=177 was sufficient to perform the CFA (power=0.99). Analysis was completed on returned baseline PDQ-20 data using SAS¨ software.

Results: Patient demographics are presented in Table 1. There was no missing PDQ-20 data. CFA model fitting was adequate (standardized root mean square residual=0.05; root mean square error of approximation=0.10; Bentler comparative fit index=0.90). All factor loadings were statistically significant (factor loading range 0.55-0.88; all t-value >9.82). All factors highly correlated with each other (correlation range: 0.87-0.97; all p<0.01). Lagrange Multiplier (LM) tests indicated that multiple alternate item-factor pathways could improve the four-factor model (ten largest significant LM statistics range from 7.92-20.78; new possible pathways for 7 items to other factors). Item 19 (forget to take medication) had low reliability to its purported factor (prospective memory; R2 =0.30). The internal consistency (Cronbachs alpha) for the four factors ranged from 0.82 to 0.91.

Conclusion:  The CFA analyses indicate that while the fit of the four-factor model for the PDQ fits, the model could be improved. Particularly concerning is the different factor-pathways for seven items, the current low item-factor reliability for item 19, and the increased correlations between factors.  In adult SLE patients, researchers and clinicians should be cautious in interpreting PDQ-20 results using the current four factors (subscales). Further validity analyses, including exploratory factor analyses, are needed.

Table 1

Socio-demographic information of recruited patients (n=208) who returned and did not return PDQ-20

PDQ-20 returned

(n=177)

PDQ-20 not returned

(n=31)

Sex

(% female)

89.8%

83.9%

Age at study visit

(mean ± SD years)

42.75 ± 12.12

41.97 ± 12.75

Age at SLE diagnosis (mean ± SD years)

28.16 ± 10.48

28.57 ± 10.19

Highest education level obtained at study visit

(% of sample*)

High-school or less 25.1%

College/University 74.9%

High-school or less 16.1%

College/University 83.9%

Employment status at study visit

(% of sample⌘)

Employed 51.7%

Retired 2.9%

Homemaker 6.9%

Student 5.2%

Disability/sick leave 27.6%

Looking for work 4.0%

Other 1.7%

Employed 73.3%

Retired 0.0%

Homemaker 3.3%

Student 6.7%

Disability/sick leave 16.7%

Looking for work 0.0%

Other 0.0%

Note: All demographic variables not statistically significantly different between groups (p>0.05); all data from baseline visits of longitudinal study.

* n=170 (7 patients missing data) for returned group; n=31 for not returned

⌘ n=174 (3 patient missing data) for returned; n=30 (1 missing) for not returned


Disclosure: L. Engel, None; J. Su, None; E. Nalder, None; Y. Goverover, None; M. Gignac, None; C. Tartaglia, None; N. Anderson, None; Z. Touma, None.

To cite this abstract in AMA style:

Engel L, Su J, Nalder E, Goverover Y, Gignac M, Tartaglia C, Anderson N, Touma Z. Confirmatory Factor Analysis of the Patient-Reported Perceived Deficits Questionnaire in Systemic Lupus Erythematosus: Cautions for Use of Subscales [abstract]. Arthritis Rheumatol. 2018; 70 (suppl 10). https://acrabstracts.org/abstract/confirmatory-factor-analysis-of-the-patient-reported-perceived-deficits-questionnaire-in-systemic-lupus-erythematosus-cautions-for-use-of-subscales/. Accessed January 27, 2021.
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