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Table 3.

Multivariate regression models for prediction of log-transformed toenail nicotine levels (ng nicotine/mg toenail) according to different reported smoking variables (n = 2,485)

Model number and tobacco exposureTobacco categorynEstimateSEPR2
Model 1       
Smoke exposure No exposure (reference group) 157 — — — 0.57 
 SHS exposure among never smokers 768 0.35 0.08 <0.0001  
 Current active smoking 771 2.59 0.08 <0.0001  
Model 2       
Smoking status Never smokers (reference group) 988 — — — 0.57 
 Past smokers 726 0.07 0.05 0.15  
 Current smokers 771 2.29 0.04 <0.0001  
SHS exposure No (reference group) 315 — — —  
 Yes 1,999 0.29 0.06 <0.0001  
Model 3       
No. cigarettes smoked per day 0 (reference group) 1,714 — — — 0.59 
 1-4 44 1.08 0.14 <0.0001  
 5-14 180 1.80 0.07 <0.0001  
 15-24 306 2.43 0.06 <0.0001  
 25-34 152 2.59 0.08 <0.0001  
 ≥35 89 2.80 0.10 <0.0001  
Model 4       
Frequency of SHS among everyone exposure No exposure (reference group) 315 — — — 0.61 
 Occasional 1,227 0.21 0.06 0.002  
 Frequent 772 0.46 0.06 <0.0001  
No. cigarettes smoked per day 0 (reference group) 1,714 — — —  
 1-4 44 1.03 0.14 <0.0001  
 5-14 180 1.76 0.07 <0.0001  
 15-24 306 2.36 0.06 <0.0001  
 25-34 152 2.50 0.08 <0.0001  
 ≥35 89 2.70 0.10 <0.0001  
Model 5 (among never smokers with SHS frequency data; n = 925)       
Frequency of SHS exposure No exposure (reference group) 157 — — — 0.04 
 Occasional 538 0.26 0.08 0.001  
 Frequent 230 0.58 0.09 <0.0001  
Model 6       
Composite smoking status Never smokers (reference group) 988 — — — 0.59 
 Past smokers 726 0.07 0.04 0.10  
 Current smokers (1-14 cigarettes per day) 224 1.69 0.07 <0.0001  
 Current smokers (15-24 cigarettes per day) 306 2.46 0.06 <0.0001  
 Current smokers (25-34 cigarettes per day) 152 2.62 0.08 <0.0001  
 Current smokers (≥35 cigarettes per day) 89 2.83 0.10 <0.0001  
Model number and tobacco exposureTobacco categorynEstimateSEPR2
Model 1       
Smoke exposure No exposure (reference group) 157 — — — 0.57 
 SHS exposure among never smokers 768 0.35 0.08 <0.0001  
 Current active smoking 771 2.59 0.08 <0.0001  
Model 2       
Smoking status Never smokers (reference group) 988 — — — 0.57 
 Past smokers 726 0.07 0.05 0.15  
 Current smokers 771 2.29 0.04 <0.0001  
SHS exposure No (reference group) 315 — — —  
 Yes 1,999 0.29 0.06 <0.0001  
Model 3       
No. cigarettes smoked per day 0 (reference group) 1,714 — — — 0.59 
 1-4 44 1.08 0.14 <0.0001  
 5-14 180 1.80 0.07 <0.0001  
 15-24 306 2.43 0.06 <0.0001  
 25-34 152 2.59 0.08 <0.0001  
 ≥35 89 2.80 0.10 <0.0001  
Model 4       
Frequency of SHS among everyone exposure No exposure (reference group) 315 — — — 0.61 
 Occasional 1,227 0.21 0.06 0.002  
 Frequent 772 0.46 0.06 <0.0001  
No. cigarettes smoked per day 0 (reference group) 1,714 — — —  
 1-4 44 1.03 0.14 <0.0001  
 5-14 180 1.76 0.07 <0.0001  
 15-24 306 2.36 0.06 <0.0001  
 25-34 152 2.50 0.08 <0.0001  
 ≥35 89 2.70 0.10 <0.0001  
Model 5 (among never smokers with SHS frequency data; n = 925)       
Frequency of SHS exposure No exposure (reference group) 157 — — — 0.04 
 Occasional 538 0.26 0.08 0.001  
 Frequent 230 0.58 0.09 <0.0001  
Model 6       
Composite smoking status Never smokers (reference group) 988 — — — 0.59 
 Past smokers 726 0.07 0.04 0.10  
 Current smokers (1-14 cigarettes per day) 224 1.69 0.07 <0.0001  
 Current smokers (15-24 cigarettes per day) 306 2.46 0.06 <0.0001  
 Current smokers (25-34 cigarettes per day) 152 2.62 0.08 <0.0001  
 Current smokers (≥35 cigarettes per day) 89 2.83 0.10 <0.0001  

NOTE: Age (y) was significant in all the models. The following were not significant in any model and were excluded from the final models: nail fungus (yes, no), nail polish (yes, no), body mass index (<21, 21-22.9, 23-24.9, 25-28.9, ≥29), physical activity (<1, 1-1.9, 2-3.9, 4-6.9, ≥7 h/wk of moderate to vigorous activity), and alcohol intake (0, 0.1-4.9, 5-14.9, ≥15 g/d).

There were 169 participants (including 63 never smokers) that did not have information about SHS and were excluded from relevant models.

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