Table 3.
Cox regression analysesa
| Univariable analysis (n = 3,352) | Multivariable analysis | |||||||
|---|---|---|---|---|---|---|---|---|
| Adjusted for age at disease onset(n = 3,352) | Adjusted for age at disease onset and sex (n = 3,352) | Adjusted for age at disease onset, sex, and immunosuppressive treatment (n = 2,887) | ||||||
| HR (95% CI) | P | HR (95% CI) | P | HR (95% CI) | P | HR (95% CI) | P | |
| Cutaneous involvement | ||||||||
| lcSSc | Reference | Reference | Reference | Reference | ||||
| dcSSc | 1.90 (1.64–2.19) | <0.001 | 2.39 (2.07–2.77) | <0.001 | 2.14 (1.85–2.48) | <0.001 | 2.03 (1.61–2.56) | <0.001 |
| C‐indexb | 0.60 ± 0.01 | 0.73 ± 0.01 | 0.75 ± 0.01 | 0.78 ± 0.02 | ||||
| 2 clusters | ||||||||
| Cluster A | Reference | Reference | Reference | Reference | ||||
| Cluster B | 2.23 (1.88–2.65) | <0.001 | 2.40 (2.02–2.85) | <0.001 | 2.26 (1.91–2.69) | <0.001 | 2.47 (1.86–3.27) | <0.001 |
| C‐indexb | 0.59 ± 0.01 | 0.72 ± 0.01 | 0.74 ± 0.01 | 0.78 ± 0.02 | ||||
| 6 clusters | ||||||||
| Cluster 1 | Reference | Reference | Reference | Reference | ||||
| Cluster 2 | 2.32 (1.62–3.31) | <0.001 | 2.10 (1.46–3.00) | <0.001 | 1.97 (1.38–2.82) | <0.001 | 1.64 (0.88–3.03) | 0.119 |
| Cluster 3 | 1.30 (0.89–1.91) | 0.172 | 1.63 (1.11–2.38) | 0.012 | 1.62 (1.11–2.37) | 0.013 | 1.97 (1.10–3.54) | 0.023 |
| Cluster 4 | 2.47 (1.86–3.27) | <0.001 | 2.49 (1.88–3.30) | <0.001 | 2.40 (1.81–3.19) | <0.001 | 2.77 (1.74–4.39) | <0.001 |
| Cluster 5 | 3.03 (2.23–4.11) | <0.001 | 3.77 (2.77–5.12) | <0.001 | 3.37 (2.47–4.58) | <0.001 | 3.22 (1.93–5.36) | <0.001 |
| Cluster 6 | 4.40 (3.30–5.87) | <0.001 | 5.85 (4.38–7.81) | <0.001 | 5.20 (3.89–6.95) | <0.001 | 6.14 (3.81–9.89) | <0.001 |
| C‐indexb | 0.63 ± 0.01 | 0.75 ± 0.01 | 0.76 ± 0.01 | 0.79 ± 0.02 | ||||
Disease onset was defined as the first non–Raynaud's phenomenon symptom (see Supplementary Table 8, available on the Arthritis & Rheumatology web site at http://onlinelibrary.wiley.com/doi/10.1002/art.40906/abstract, for sensitivity analysis using the onset of Raynaud's phenomenon as the definition of disease onset). HR = hazard ratio; 95% CI = 95% confidence interval; lcSSc = limited cutaneous systemic sclerosis; dcSSc = diffuse cutaneous systemic sclerosis.
The C‐index was calculated for each Cox regression model, and corresponds to the estimation of the probability of concordance, equivalent to the area under the receiver operating characteristic curve for logistic regression models. A value of 1 indicates perfect agreement and 0.5 indicates an agreement that is no better than chance. Values for the C‐index are the mean ± SEM.