Investigators of the Canadian Scleroderma Research Group are shown in Appendix A.
Special Theme Articles: Vascular Comordibidity in the Rheumatic Diseases
Modeling smoking in systemic sclerosis: A comparison of different statistical approaches
Version of Record online: 30 MAR 2011
Copyright © 2011 by the American College of Rheumatology
Arthritis Care & Research
Volume 63, Issue 4, pages 570–578, April 2011
How to Cite
Hudson, M., Lo, E., Baron, M., Steele, R. and Canadian Scleroderma Research Group (2011), Modeling smoking in systemic sclerosis: A comparison of different statistical approaches. Arthritis Care Res, 63: 570–578. doi: 10.1002/acr.20416
- Issue online: 30 MAR 2011
- Version of Record online: 30 MAR 2011
- Accepted manuscript online: 6 DEC 2010 11:47AM EST
- Manuscript Accepted: 22 NOV 2010
- Manuscript Received: 1 JUL 2010
- Canadian Institutes of Health Research
- Scleroderma Society of Canada
- Educational grants from Actelion Pharmaceuticals and Pfizer, Inc.
- New Investigator awards from the Canadian Institutes of Health Research and the Fonds de la Recherche en Santé du Québec
To determine the effect of different methods of modeling smoking on vascular outcomes in rheumatic diseases.
Data from the Canadian Scleroderma Research Group Registry were used. Patients self-reported their smoking history. Vascular outcomes were severity of Raynaud's phenomenon, presence of finger ulcers, and severity of finger ulcers. Several models were developed to capture the experience of smoking: 1) ever compared to never smoking; 2) current and past smoking compared to never smoking; 3) never, past, and current smoking compared using polynomial contrasts; 4) smoking intensity, duration, and time since cessation assessed separately; and 5) smoking modeled using the Comprehensive Smoking Index (CSI), which integrates intensity, duration, and time since cessation into a single covariate.
This study included 606 patients, of which 16% were current, 42% were past, and 42% were never smokers. Current and past smokers smoked a mean ± SD of 25 ± 17 and 17 ± 18 pack-years, respectively. Smoking duration was shorter in past compared to current smokers (18.3 versus 31.7 years). Past smokers reported having stopped smoking approximately mean ± SD 16 ± 12 years prior, although this ranged from 1 to 50 years. Smoking had no effect on vascular outcomes in the simplest model comparing ever to never smokers. Models that isolated past smokers revealed the presence of a healthy smoker bias in that group. The model using the CSI demonstrated a strong negative effect of smoking on vascular outcomes.
Proper modeling of the effect of smoking is essential in studies of vascular outcomes of rheumatic diseases.