Association of Poverty Income Ratio with Physical Functioning in a Cohort of Patients with Systemic Lupus Erythematosus Open Access

Hoge, Courtney (Spring 2018)

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Background: Lower socioeconomic status (SES) is associated with poor physical functioning in systemic lupus erythematosus (SLE) patients; however, previous studies have not used poverty income ratio (PIR) as a proxy for SES in this population. Additionally, multi-component functional assessments are a novel approach in SLE. Thus, we examined the association of poverty income ratio (PIR) with self-reported physical functioning in a cohort of SLE patients and examined whether this association was similar for self-reported physical functioning and a set of complementary measures of physical functioning.

Methods: We used cross-sectional data on 744 participants from the ongoing Georgians Organized Against Lupus (GOAL) cohort, and secondary analyses used data on 56 participants from a GOAL-ancillary pilot study. Primary analyses utilized multivariable linear regression to estimate the association between PIR (categorized as <1.00, 1.00-1.99, 2.00-3.99, and ≥4.00) and physical functioning (PF; scaled subscore from Short Form-12 survey). Secondary analyses summarized complementary measures of physical functioning as means or percentages by PIR (categorized as <1.00, 1.00-1.99, and ≥2.00).

Results: Overall, the mean age of participants was 48.0 years; 6.7% were male; 80.9% were black; and 37.5%, 21.0%, 29.6% and 12.0% had PIRs of <1.00, 1.00-1.99, 2.00-3.99, and ≥4.00, respectively. The overall mean PF score was 45.8 (36.2, 40.7, 55.5, and 61.2 for PIRs of <1.00, 1.00-1.99, 2.00-3.99, and ≥4.00, respectively). With adjustment, higher PIRs (<1.00, 2.00-3.99, and ≥4.00, respectively vs. 1.00-1.99) remained associated (𝛽(95% CI)) with higher PF scores (-6.0 (-12.8 to 0.8), 10.9 (3.3 to 18.6), and 16.2 (6.4 to 26.0)). In secondary analyses, increased PIR was associated with better physical functioning, in that participants with higher PIRs, on average, had higher scores for measures of physical performance, were less likely to report difficulty with activities of daily living, and had fewer falls in the prior year. 

Conclusion: Our results show that higher SES is associated with improved physical functioning across multiple domains, warranting further research into multi-component functional assessments to develop individual treatment plans and potentially improve disparities in outcomes. 

Table of Contents

Background - 1

Methods - 7

Study Populations and Data Sources - 7

Study Variables - 8

Statistical Analysis - 11

Results - 13

Characteristics of the SLE Cohort - 13

Association of PIR with Self-Reported PF in GOAL - 13

Stratified Association of PIR with Self-Reported PF in GOAL - 14

Sensitivity Analyses - 15

Complementary PF Measures in APPEAL - 15

Discussion - 17

References - 23

Tables - 30

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