Stepwise multiple linear regression analysis of serum Clara cell secretory protein 16 (CC16), surfactant-associated protein (SP)-A and -B
| r2 | F | p-value | β | |
| Nonsmokers | ||||
| CC16 | ||||
| Age | 0.29 | 25.1 | 0.0000 | 0.54 |
| SP-A | ||||
| Creatinine | 0.08 | 5.1 | 0.027 | −0.28 |
| SP-B | ||||
| Creatinine | 0.25 | 20.3 | 0.0000 | −0.50 |
| Smokers | ||||
| SP-B | ||||
| Pack-yrs | 0.52 | 48.3 | 0.0000 | 0.72 |
| Cigarette·day−1 | 0.15 | 8.3 | 0.0059 | 0.39 |
| Combined | ||||
| CC16 | 0.35 | 24.4 | 0.0000 | |
| Age | 0.0000 | 0.56 | ||
| Pack-yrs | 0.0062 | −0.23 | ||
| SPA | 0.14 | 7.4 | 0.001 | |
| Creatinine | 0.004 | −0.28 | ||
| Pack-yrs | 0.0121 | 0.24 | ||
| SP-B | 0.62 | 76.2 | 0.0000 | |
| Creatinine | 0.0000 | −0.33 | ||
| Pack-yrs | 0.0000 | 0.72 |
Determinants of CC16, SP-A and SP-B identified using stepwise multiple linear regression analysis where independent variables with the least significance (p>0.05) were sequentially omitted
The authors hypothesised that the independent variables influencing serum CC16, SP-A, and SP-B were tobacco smoke exposure, serum creatinine, age and sex
Tobacco smoking was expressed as cumulative smoking (pack-yrs) and current smoking (cigarettes·day−1)