Skip to main content

Table 5 Instrumental variable analysis results

From: The effect on survival of continuing chemotherapy to near death

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)  
  1. Abbreviation: CI, confidence interval; SE, standard error.
  2. * 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.
  3. † P < 0.001
  4. ‡ Unadjusted survival derived from Kaplan-Meier method
  5. § 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.
  6. || 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