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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