Table 5.
Cox regression predictive models prepared for lung cancer in all of the PLCO control subjects (model 1) and in smokers only (model 2)*
| Variable | Model 1c† |
Model 2c‡ |
||
| All PLCO control arm (N = 61 986), HR (95% CI) | P | Smokers only in PLCO control arm (N = 33 039), HR (95% CI) | P | |
| Age, per year | ||||
| Age spline 1 | 1.166 (1.071 to 1.271) | <.001 | 1.198 (1.090 to 1.317) | <.001 |
| Age spline 2 | 0.785 (0.596 to 1.035) | .086 | 0.761 (0.550 to 1.052) | .098 |
| Age spline 3 | 1.666 (0.829 to 3.348) | .152 | 1.907 (0.766 to 4.747) | .165 |
| Education, per 1 of 7 levels change | 0.923 (0.884 to 0.963) | .001 | 0.921 (0.881 to 0.962) | <.001 |
| BMI, per 1 unit change | 0.972 (0.957 to 0.987) | <.001 | 0.974 (0.959 to 0.990) | .001 |
| Family history of lung cancer, yes vs no | 1.561 (1.330 to 1.832) | <.001 | 1.555 (1.317 to 1.835) | <.001 |
| COPD, yes vs no | 1.446 (1.218 to 1.715) | <.001 | 1.442 (1.212 to 1.714) | <.001 |
| Chest x-ray in past 3 y, per 1 of 3 levels | 1.109 (1.017 to 1.208) | .019 | 1.111 (1.016 to 1.215) | .021 |
| Pack-years smoked, per 1 pack-year | ||||
| PKYR spline 1 | 1.106 (1.072 to 1.141) | <.001 | 1.058 (1.043 to 1.073) | <.001 |
| PKYR spline 2 | 0.505 (0.398 to 0.640) | <.001 | 0.950 (0.936 to 0.965) | <.001 |
| Smoking duration, linear, per 1 y | 1.014 (0.998 to 1.032) | .111 | ||
| Smoking duration, splines, per 1 y | ||||
| Duration spline 1 | 0.987 (0.950 to 1.025) | .484 | ||
| Duration spline 2 | 1.132 (1.026 to 1.250) | .014 | ||
| Smoking quit-time in smokers, per 1 y | ||||
| Quit-time spline 1 | 0.946 (0.918 to 0.974) | <.001 | ||
| Quit-time spline 2 | 1.048 (1.012 to 1.085) | .008 | ||
| Smoking status | ||||
| Never/former | Baseline | <.001 | Baseline | .011 |
| Current | 1.687 (1.406 to 2.024) | 1.337 (1.070 to 1.670) | ||
| Model performance statistics | ||||
| C statistic | 0.8606 | 0.8101 | ||
These Cox models parallel the logistic models presented in Table 3. BMI = body mass index; CI = confidence interval; PKYR = pack-years; HR = hazard ratio; PLCO = Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial.
Splines for age, pack-years smoked, and smoking duration in model 1c are based on all PLCO control subjects. Knots for age were at 55, 60, 65, and 72 years. Knots for pack-years were at 0, 2.25, and 49 pack-years. Knots for smoking duration were at 0, 6, and 41 years.
Splines for age, pack-years smoked, and quit-time in model 2c are based on the distribution of these variables in smokers only. Knots for age were at 55, 60, 64, and 72 years. Knots for pack-years were at 3.25, 23.25, and 63 pack-years. Knots for quit-time were at 0, 15, and 35 years.