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

Saito et al. BMC Palliative Care 2011 10:14   doi:10.1186/1472-684X-10-14

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