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Arthritis Care Res (Hoboken). 2011 Apr;63(4):570-8. doi: 10.1002/acr.20416.

Modeling smoking in systemic sclerosis: a comparison of different statistical approaches.

Author information

1
Jewish General Hospital and McGill University, Montreal, Quebec, Canada. marie.hudson@mcgill.ca

Abstract

OBJECTIVE:

To determine the effect of different methods of modeling smoking on vascular outcomes in rheumatic diseases.

METHODS:

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.

RESULTS:

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.

CONCLUSION:

Proper modeling of the effect of smoking is essential in studies of vascular outcomes of rheumatic diseases.

PMID:
21452268
DOI:
10.1002/acr.20416
[Indexed for MEDLINE]
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