Relationship between income and mortality in a Canadian family practice cohort

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Figure 1.
Residence locations of the study patients: Each patient is represented by a circle. The clinic is located in downtown Toronto, Ont.
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Figure 2.
Relative survival of the patient cohort compared with the general population of Ontario during 9 years of follow-up: The shaded band is the 95% CI around the relative survival curve.

Table 1.

Patient demographic characteristics

CHARACTERISTICS	FEMALE PATIENTS (N = 317)	MALE PATIENTS (N = 202)
Median (IQR) age, y	58 (50 to 67)	62 (52 to 69)
Median (IQR) BMI, kg/m²	24.3 (22.1 to 27.7)	25.7 (23.6 to 27.4)
Median (IQR) neighbourhood income (based upon postal code linkage to census), $	46 000 (35 000–63 000)	48 000 (34 000–62 000)
High school graduate, n (%)	267 (86)	162 (83)
Born in Canada, n (%)	176 (56)	107 (53)
Alcohol use in the year before the survey, n (%)
• None	57 (18)	24 (12)
• ≤ 1 per week	151 (48)	81 (41)
• ≥ 1 per week	106 (34)	95 (48)
Ever smoked cigarettes, n (%)	176 (56)	133 (66)
Cancer diagnosis,^* n (%)	77 (24)	59 (29)
Hypertension,^* n (%)	134 (42)	76 (38)
Diabetes,^* n (%)	39 (12)	37 (18)
Household income per annum (imputed), n (%)
• < $20 000	35 (11)	20 (10)
• $20 000 to < $40 000	50 (16)	30 (15)
• $40 000 to < $60 000	47 (15)	25 (12)
• $60 000 to < $80 000	35 (11)	18 (9)
• ≥ $80 000	150 (47)	109 (54)
Categorical income of < $60 000 per annum, n (%)	132 (42)	75 (37)

Table 2.

Health-related behaviour and personal factors, by income and sex

HEALTH-RELATED BEHAVIOUR AND PERSONAL FACTORS	INCOME < $60 000		INCOME ≥ $60 000

	MALE	FEMALE	MALE	FEMALE
BMI (centred), kg/m², mean (95% CI)	0.29 (−0.5 to 1.1)	1.32 (0.2 to 2.5)	0.24 (−0.4 to 0.8)	−0.99 (−1.6 to −0.4)
Ever smoked daily, % (95% CI)	63 (52 to 74)	52 (43 to 60)	57 (48 to 65)	46 (39 to 53)
Current smoker, % (95% CI)	13 (6 to 21)	17 (11 to 24)	4 (1 to 7)	9 (5 to 13)
Never drank alcohol in the past year, % (95% CI)	20 (11 to 30)	28 (20 to 36)	9 (4 to 15)	12 (7 to 17)
Born in Canada, % (95% CI)	51 (39 to 62)	49 (41 to 58)	55 (46 to 64)	60 (53 to 67)
High school graduate, % (95% CI)	65 (54 to 76)	79 (72 to 86)	94 (89 to 98)	91 (87 to 96)
Diabetes, % (95% CI)	27 (17 to 37)	17 (10 to 23)	13 (7 to 19)	9 (5 to 13)
Hypertension, % (95% CI)	43 (31 to 54)	47 (38 to 56)	35 (26 to 43)	39 (32 to 46)
Cancer, % (95% CI)	27 (17 to 37)	25 (18 to 32)	31 (23 to 39)	24 (18 to 30)

Table 3.

The results of the regression model examining explanatory variables for mortality: The model is adjusted for age and BMI.

RISK FACTOR	RELATIVE RISK (95% CI)
Female vs male	0.47 (0.27 to 0.82)
Imputed income (categorical variable with 5 categories, treated as continuous from low to high income)	0.75 (0.59 to 0.96)
High school graduate vs non-graduate	1.05 (0.54 to 2.04)
Born in Canada vs immigrant	1.76 (0.99 to 3.12)
Ever smoked daily vs never smoked daily	2.17 (1.15 to 4.09)
Alcohol use during the previous year
• > 1 drink per week	1.0 (reference)
• ≤ 1 drink per week	1.91 (0.90 to 4.02)
• None	4.22 (1.81 to 9.85)
Diabetes diagnosis before survey	2.74 (1.46 to 5.13)
Hypertension before survey	1.39 (0.76 to 2.53)
Cancer before survey	1.93 (1.07 to 3.50)

Table 4.

Final model with different income parameterizations

INCOME PARAMETERIZATION	RATE RATIO (95% CI)
Parameterization 1
Categorical income (as continuous variable)	0.75 (0.59 to 0.95)
Parameterization 2
Categorical income (by categories) per annum
• < $20 000	1.0 (reference)
• $20 000 to < $40 000	0.81 (0.35 to 1.88)
• $40 000 to < $60 000	0.98 (0.40 to 2.42)
• $60 000 to < $80 000	0.17 (0.02 to 1.30)
• ≥ $80 000	0.34 (0.12 to 0.97)
Parameterization 3
Income of < $60 000 per annum vs income of ≥ $60 000 per annum	2.18 (1.18 to 4.02)