Table 5.
Instrumental variable analysis results
| Model | Patient population | Variable used for classification | Variables | Lowest quintile | Second quintile | Third quintile | Fourth quintile | Highest quintile | Instrumental variable estimate |
|---|---|---|---|---|---|---|---|---|---|
| 1 | All patients (n = 7,879) |
Prevalence of "chemotherapy" | Number of patients* | 1,492 | 1,388 | 1,439 | 1,255 | 2,139 | |
| Chemotherapy recipients, %† | 30.8 | 43.4 | 47.5 | 49.8 | 52.3 | ||||
| Aggressive-approach chemotherapy recipients, %† | 2.2 | 3.2 | 4.2 | 5.1 | 4.4 | ||||
| Age at diagnosis, years | 73.0 | 73.3 | 72.8 | 73.3 | 72.8 | ||||
| Female, % | 42.2 | 41.7 | 42.6 | 48.3 | 39.8 | ||||
| non-Hispanic white, % | 83.7 | 85.4 | 88.1 | 71.9 | 82.8 | ||||
| Socioeconomic status, mean quintile | 2.9 | 2.8 | 3.0 | 3.1 | 3.0 | ||||
| Without comorbidity, % | 78.2 | 73.7 | 74.5 | 69.8 | 69.1 | ||||
| Survival at 1 year after diagnosis, %‡ | 21.7 ± 1.1 | 23.5 ± 1.1 | 22.2 ± 1.1 | 21.7 ± 1.2 | 23.7 ± 0.9 | 6.7% (95%CI: -6.6, 19.9) | |||
| Survival at 2 years after diagnosis, %‡ | 5.6 ± 0.6 | 6.7 ± 0.7 | 6.1 ± 0.6 | 4.8 ± 0.6 | 6.8 ± 0.5 | 1.7% (95%CI: -5.9, 9.3) | |||
| Hazard Ratio (95%CI)§ | 1.0 | 0.94 (0.87, 1.01) | 0.96 (0.89, 1.03) | 1.04 (0.96, 1.12) | 0.93 (0.87, 0.99) | ||||
| 2 | Chemotherapy recipients (n = 3,534) |
Prevalence of "aggressive-approach chemotherapy" | Number of patients|| | 453 | 136 | 990 | 619 | 614 | |
| Chemotherapy recipients, % | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | ||||
| Aggressive-approach chemotherapy recipients, %† | 4.6 | 6.6 | 7.7 | 10.3 | 12.1 | ||||
| Age at diagnosis, years | 71.7 | 71.7 | 71.1 | 71.7 | 71.9 | ||||
| Female, % | 43.7 | 44.1 | 38.6 | 41.7 | 43.3 | ||||
| non-Hispanic white, % | 89.0 | 83.8 | 84.6 | 86.0 | 74.8 | ||||
| Socioeconomic status, mean quintile | 3.0 | 3.3 | 3.2 | 3.2 | 3.2 | ||||
| Without comorbidity, % | 73.5 | 78.7 | 70.6 | 79.2 | 68.2 | ||||
| Survival at 1 year after diagnosis, %‡ | 30.5 ± 2.2 | 29.4 ± 3.9 | 26.0 ± 1.4 | 26.3 ± 1.8 | 27.9 ± 1.8 | -53.5% (95%CI: -124.1, 17.2) | |||
| Survival at 2 years after diagnosis, %‡ | 8.4 ± 1.3 | 8.1 ± 2.3 | 7.4 ± 0.8 | 6.5 ± 1.0 | 6.2 ± 1.0 | -35.1% (95%CI: -76.9, 6.6) | |||
| Hazard Ratio (95%CI)§ | 1.0 | 1.05 (0.87, 1.28) | 1.07 (0.96, 1.20) | 1.11 (0.98, 1.25) | 1.11 (0.99, 1.26) |
Abbreviation: CI, confidence interval; SE, standard error.
* A total of 166 patients who reside in the Health Care Service Areas, where there were five or fewer patients treated with or without chemotherapy, were excluded.
† P < 0.001
‡ Unadjusted survival derived from Kaplan-Meier method
§ Adjusted hazard ratios and 95% confidence intervals derived from Cox proportional hazards regression model. Patient age, gender, race/ethnicity, socioeconomic status quintiles, Charlson comorbidity index, and year of death were included in the model.
|| A total of 722 patients who reside in the Health Care Service Areas, where there were five or fewer patients treated with or without aggressive-approach chemotherapy, were excluded