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Table 4 Backward stepwise multiple linear regression for physical component summary (PCS) and mental component summary (MCS)

From: Association of the lupus low disease activity state (LLDAS) with health-related quality of life in a multinational prospective study

Model Variable Model 1 Model 2 Model 3
Common variables   PCS MCS PCS MCS PCS MCS
   Coeff p Coeff p Coeff p Coeff p Coeff p Coeff p
Model 1 Country
Australia reference - 1.05 0.10 reference - 1.04 0.19 reference - 1.06 0.08
China 1.04 0.09 reference - 1.06 0.02 reference - 1.05 0.04 reference -
Indonesia 1.01 0.73 1.06 0.04 1.02 0.40 1.07 0.03 1.02 0.45 1.07 0.02
Philippines 1.10 <0.001 1.17 <0.001 1.12 <0.001 1.18 <0.001 1.12 <0.001 1.19 <0.001
Singapore 1.08 <0.01 1.12 <0.001 1.09 <0.001 1.12 <0.001 1.09 <0.001 1.13 <0.001
Taiwan 1.06 0.01 1.04 0.08 1.07 <0.01 1.03 0.15 1.06 0.01 1.03 0.14
Thailand 1.04 0.11 1.02 0.33 1.05 0.06 1.02 0.39 1.04 0.12 1.02 0.30
Ethnicity
Caucasian reference - reference - reference - reference - reference - reference -
Asian 1.10 <0.001 1.02 0.50 1.10 <0.001 1.02 0.62 1.10 <0.001 1.02 0.53
Education
Primary reference - reference - reference - reference - reference - reference -
Secondary 1.03 0.03 1.03 0.12 1.03 0.03 1.03 0.16 1.03 0.04 1.03 0.13
Tertiary 1.05 0.002 1.06 <0.01 1.05 0.001 1.06 <0.01 1.05 0.001 1.06 <0.01
Age at diagnosis (years) 0.997 <0.001 1.00 0.39 0.997 <0.001 1.00 0.39 0.997 <0.001 1.00 0.37
Disease duration (years) 0.998 0.05 1.00 0.06 0.998 <0.01 1.00 0.08 0.998 <0.01 1.00 0.10
SLICC-DI score 0.96 <0.001 0.99 0.13 0.96 <0.001 0.99 0.21 0.97 <0.001 0.99 0.15
LLDAS 1.06 <0.001 1.05 <0.001 - - - - - - - -
Model 2 SLEDAI score - - - - 0.997 0.05 1.00 0.35 - - - -
PGA (0–3) - - - - 0.95 <0.001 0.97 0.02 - - - -
Mild flare - - - - 0.98 0.26 0.98 0.25 - - - -
Severe flare - - - - 0.97 0.11 0.97 0.33 - - - -
Prednisolone (mg) - - - - 0.998 0.01 0.999 0.13 - - - -
Model 3 Current organ activity
Renal - - - - - - - - 1.00 0.43 1.02 0.29
MSK - - - - - - - - 0.93 <0.001 0.99 0.55
Vasculitis - - - - - - - - 0.99 0.84 1.02 0.74
Cutaneous - - - - - - - - 0.95 0.70 0.94 0.04
Serositis - - - - - - - - 0.96 0.34 1.04 0.49
PGA (0–3) - - - - - - - - 0.99 <0.001 0.97 0.03
Mild flare - - - - - - - - 0.99 0.59 0.99 0.58
Severe flare - - - - - - - - 0.96 0.04 0.98 0.36
Prednisolone (mg) - - - - - - - - 0.998 <0.01 0.999 0.19
  1. Variables with p values ≤0.1 in simple linear regression analysis were checked for multicollinearity prior to inclusion in the models. To account for different measures of disease activity and disease state that were collinear and to ascertain which of the LLDAS criteria contributed to the relationship with health-related quality of life, three models were used: Model 1 - disease state measured as lupus low disease activity state (LLDAS); Model 2 - breakdown of LLDAS into its individual components/criteria representing measures of disease activity – the systemic lupus erythematosus disease activity index (SLEDAI) score, physician global assessment (PGA), flare index and prednisolone dose; Model 3 - breakdown of SLEDAI score by current organ activity, and PGA, flare index and prednisolone dose. Common independent variables used in all three models are at the top of the table and include: country, ethnicity, education, age at diagnosis, disease duration and Systemic Lupus International Collaborating Clinics (SLICC)-damage index (DI) score. Coefficient (Coeff) is based on log-linear model and back-transformed using the exponential function. This represents (coeff-1)*100% increase/decrease in PCS or MCS scores for change in category (categorical variables), or (coeff-1)*100% change per one unit (continuous variables). Abbreviations: CNS (cntral nervous system, MSK musculoskeletal. P values in italics are significant