11
Province-Level Income Inequality and Health Outcomes in Canadian Adolescents Elizabeth C. Quon, 1 PHD, and Jennifer J. McGrath, 2 PHD, MPH 1 Community Mental Health, IWK Health Centre and 2 Department of Psychology, Concordia University All correspondence concerning this article should be addressed to Jennifer J. McGrath, PHD, MPH, Pediatric Public Health Psychology Laboratory, Department of Psychology, Concordia University, 7141 Sherbrooke St. W., Montreal, Quebec H4B 1R6, Canada. E-mail: [email protected] Received February 17, 2014; revisions received September 9, 2014; accepted September 17, 2014 Objective To examine the effects of provincial income inequality (disparity between rich and poor), independent of provincial income and family socioeconomic status, on multiple adolescent health outcomes. Methods Participants (aged 12–17 years; N ¼ 11,899) were from the Canadian National Longitudinal Survey of Children and Youth. Parental education, household income, province income inequal- ity, and province mean income were measured. Health outcomes were measured across a number of do- mains, including self-rated health, mental health, health behaviors, substance use behaviors, and physical health. Results Income inequality was associated with injuries, general physical symptoms, and limiting conditions, but not associated with most adolescent health outcomes and behaviors. Income inequality had a moderating effect on family socioeconomic status for limiting conditions, hyperactivity/inattention, and con- duct problems, but not for other outcomes. Conclusions Province-level income inequality was associated with some physical and mental health outcomes in adolescents, which has research and policy implications for this age-group. Key words adolescents; disparities; health behavior; mental health; public health. Countries with greater disparity between the rich and the poor—or greater income inequality—have been shown to have worse population health (see Wilkinson & Pickett, 2006 for a summary). These findings have formed the basis of the income inequality hypothesis: A more unequal distribution of income in society, over and above societal average income, has an adverse effect on the health of the individuals in that society (Wilkinson & Pickett, 2007). To test the hypothesis that income inequality has a contextual effect on health, Subramanian and Kawachi (2004) have argued that multilevel consideration of individual income and societal/community income inequality, and their ef- fects on individual health, is essential. In a meta-analysis of 28 multilevel studies, Kondo et al. (2009) found that income inequality had a ‘‘modest’’ adverse effect on adult self-rated health and mortality. Adolescence is a period of transition from childhood to adulthood. During this time, one’s socioeconomic status (SES) also shifts from being determined by one’s parents or family toward being primarily self-determined. Existing ev- idence suggests that graded associations between SES and health (or socioeconomic gradients in health), which are well-established in adulthood and childhood (Braveman, Cubbin, Egerter, Williams, & Pamuk, 2010), may be pre- sent inconsistently during adolescence (Chen, Martin, & Matthews, 2006; Goodman, 1999; West, 1997). Similarly, associations between income inequality and health may be different in adolescence compared with adulthood. Two main mechanisms have been proposed to explain the link between income inequality and health, both of which may differentially affect adolescent versus adult health. The social cohesion pathway suggests that income inequality leads to low social capital and stressful social comparison, which affect health through psychological pro- cesses and associated physiological changes (Wilkinson, 1997a, b; Wilkinson & Pickett, 2009). Social comparison Journal of Pediatric Psychology pp. 111, 2014 doi:10.1093/jpepsy/jsu089 Journal of Pediatric Psychology ß The Author 2014. Published by Oxford University Press on behalf of the Society of Pediatric Psychology. All rights reserved. For permissions, please e-mail: [email protected] Journal of Pediatric Psychology Advance Access published October 15, 2014 at University of Birmingham on October 31, 2014 http://jpepsy.oxfordjournals.org/ Downloaded from

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Page 1: Province-Level Income Inequality and Health Outcomes in Canadian Adolescents

Province-Level Income Inequality and Health Outcomesin Canadian Adolescents

Elizabeth C. Quon,1 PHD, and Jennifer J. McGrath,2 PHD, MPH1Community Mental Health, IWK Health Centre and 2Department of Psychology, Concordia University

All correspondence concerning this article should be addressed to Jennifer J. McGrath, PHD, MPH, Pediatric

Public Health Psychology Laboratory, Department of Psychology, Concordia University, 7141 Sherbrooke St.

W., Montreal, Quebec H4B 1R6, Canada. E-mail: [email protected]

Received February 17, 2014; revisions received September 9, 2014; accepted September 17, 2014

Objective To examine the effects of provincial income inequality (disparity between rich and poor),

independent of provincial income and family socioeconomic status, on multiple adolescent health

outcomes. Methods Participants (aged 12–17 years; N¼ 11,899) were from the Canadian National

Longitudinal Survey of Children and Youth. Parental education, household income, province income inequal-

ity, and province mean income were measured. Health outcomes were measured across a number of do-

mains, including self-rated health, mental health, health behaviors, substance use behaviors, and physical

health. Results Income inequality was associated with injuries, general physical symptoms, and limiting

conditions, but not associated with most adolescent health outcomes and behaviors. Income inequality had a

moderating effect on family socioeconomic status for limiting conditions, hyperactivity/inattention, and con-

duct problems, but not for other outcomes. Conclusions Province-level income inequality was associated

with some physical and mental health outcomes in adolescents, which has research and policy implications

for this age-group.

Key words adolescents; disparities; health behavior; mental health; public health.

Countries with greater disparity between the rich and the

poor—or greater income inequality—have been shown to

have worse population health (see Wilkinson & Pickett,

2006 for a summary). These findings have formed the

basis of the income inequality hypothesis: A more unequal

distribution of income in society, over and above societal

average income, has an adverse effect on the health of the

individuals in that society (Wilkinson & Pickett, 2007). To

test the hypothesis that income inequality has a contextual

effect on health, Subramanian and Kawachi (2004) have

argued that multilevel consideration of individual income

and societal/community income inequality, and their ef-

fects on individual health, is essential. In a meta-analysis

of 28 multilevel studies, Kondo et al. (2009) found that

income inequality had a ‘‘modest’’ adverse effect on adult

self-rated health and mortality.

Adolescence is a period of transition from childhood

to adulthood. During this time, one’s socioeconomic status

(SES) also shifts from being determined by one’s parents or

family toward being primarily self-determined. Existing ev-

idence suggests that graded associations between SES and

health (or socioeconomic gradients in health), which are

well-established in adulthood and childhood (Braveman,

Cubbin, Egerter, Williams, & Pamuk, 2010), may be pre-

sent inconsistently during adolescence (Chen, Martin, &

Matthews, 2006; Goodman, 1999; West, 1997). Similarly,

associations between income inequality and health may be

different in adolescence compared with adulthood. Two

main mechanisms have been proposed to explain the

link between income inequality and health, both of

which may differentially affect adolescent versus adult

health. The social cohesion pathway suggests that income

inequality leads to low social capital and stressful social

comparison, which affect health through psychological pro-

cesses and associated physiological changes (Wilkinson,

1997a, b; Wilkinson & Pickett, 2009). Social comparison

Journal of Pediatric Psychology pp. 1–11, 2014

doi:10.1093/jpepsy/jsu089

Journal of Pediatric Psychology � The Author 2014. Published by Oxford University Press on behalf of the Society of Pediatric Psychology.All rights reserved. For permissions, please e-mail: [email protected]

Journal of Pediatric Psychology Advance Access published October 15, 2014 at U

niversity of Birm

ingham on O

ctober 31, 2014http://jpepsy.oxfordjournals.org/

Dow

nloaded from

Page 2: Province-Level Income Inequality and Health Outcomes in Canadian Adolescents

and social cohesion may be particularly relevant to health

during adolescence, owing to the importance of peer rela-

tions during this time (West, 1997). Psychosocial pro-

cesses are also critical during this developmental period,

and mental disorders are the most common health prob-

lems (Gore et al., 2011). The policy pathway suggests that

the adverse influence of income inequality may operate

through social and health policies, such as health care,

welfare spending, child care, tax policy, and unemploy-

ment compensation (Subramanian & Kawachi, 2004).

Policies and spending related to education and mental

health care may be particularly important during

adolescence.

To date, only a handful of studies have examined asso-

ciations between income inequality and adolescent health

outcomes with multilevel study designs. Using data from

the Health Behaviour in School-aged Children study, greater

income inequality at the country level has been shown to be

related to poorer adolescent self-related health (although

results did not control for country mean income;

Torsheim, Currie, Boyce, & Samdal, 2006), drinking alco-

hol in young adolescents (with no effect in older adoles-

cents; Elgar, Roberts, Parry-Langdon, & Boyce, 2005), and

a steeper within-country socioeconomic gradient in adoles-

cent life satisfaction (but no main effect of income inequality

on life satisfaction; Levin et al., 2011). In the United States,

greater state-level income inequality was linked to higher

adolescent obesity prevalence (Singh, Kogan, & van Dyck,

2008) and lower physical activity levels (Singh, Kogan,

Siahpush, & van Dyck, 2009), although these findings did

not control for state mean income. State-level income in-

equality was inversely correlated with birth-control usage

but was not significant in multivariate analyses (Crosby,

Holtgrave, DiClemente, Wingood, & Gayle, 2003).

Finally, higher municipal-level income inequality was asso-

ciated with worse oral health in Brazilian adolescents

(Celeste, Nadanovsky, Ponce de Leon, & Fritzell, 2009).

Results from these studies suggest that associations

between income inequality and adolescent health may

vary by health outcomes, such that income inequality

may have a stronger effect on certain health outcomes.

Moreover, associations between SES and adolescent

health have been shown to vary by health outcome

(Goodman, 1999). Examination of multiple health out-

comes within a single sample would help to elucidate

how income inequality may be differentially linked to

health outcomes. To date, no studies have examined asso-

ciations between income inequality and mental health out-

comes, a critical domain of adolescent health. Moreover,

some of the previous findings did not statistically control

for country/state mean income, which limits their inter-

pretability, as this is a potential confounder of the influ-

ence of country/state income inequality.

It also remains unclear whether the geographical scale

(e.g., country, state, city) of income inequality comparison

matters for adolescent health. Existing evidence in adults,

as reported in the meta-analysis by Kondo et al. (2009),

suggests that stronger associations between income in-

equality and self-rated health exist for between-country

versus within-country comparisons. Moreover, meta-ana-

lytic findings suggest that within-country associations

may emerge in highly unequal societies only. Ross et al.

(2005) found that within-country city-level income in-

equality was linked to mortality in highly unequal

countries (United States, United Kingdom) but not in

more equal countries (Canada, Sweden, Australia). To

date, within-country adolescent comparisons are limited

to U.S. states (Crosby et al., 2003; Singh et al., 2008,

2009) and Brazilian municipalities (Celeste et al., 2009).

There is a need for more within-country comparisons out-

side of the United States, particularly in more equal

countries, like Canada. In terms of income inequality,

Canada is more equal than the United States, United

Kingdom, Italy, Australia, and Japan, and less equal than

Switzerland, Ireland, France, Sweden, Denmark, and other

peer countries (Conference Board of Canada, 2013).

Canada is made up of 10 provinces and 3 territories.

Each province is responsible for its funding and delivery

of health, social, and educational services. Canadian prov-

inces also vary widely in terms of level of taxation. For

instance, the highest provincial taxation rate in Alberta is

10%, while it is 21% in Nova Scotia. As such, Canadian

provinces differ in terms of level of income inequality as

well as in the provision of programs and services.

Therefore, examination of the scale of income inequality

at the province level was thought to be the most appropri-

ate within-country comparison for the Canadian context.

To our knowledge, no previous studies have tested for the

effects of income inequality on adolescent health within

Canada. Further understanding of how geographical scale

and the inequality level of the country affects within-coun-

try effects may help to elucidate the mechanisms by which

income inequality may influence health.

The aim of the current study was to test the effects of

provincial income inequality, independent of province

mean income and family SES, across a number of health

outcomes in Canadian adolescents. Therefore, using a

within-country design, we tested a contextual main effect

of province-level income inequality on individual health

outcomes in adolescents, while controlling for province

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Page 3: Province-Level Income Inequality and Health Outcomes in Canadian Adolescents

mean income, household income, and parental education.

We expected that greater provincial income inequality

would be associated with worse adolescent health out-

comes. We also tested the interaction between province-

level income inequality and family SES on adolescent

health. We expected stronger associations between family

SES and adolescent health (or steeper socioeconomic gra-

dients in health) in more unequal provinces.

MethodSample

Participants were from the National Longitudinal Survey of

Children and Youth (NLSCY), a population-based longitu-

dinal survey of Canadian children and adolescents con-

ducted by Statistics Canada and Human Resources

Development Canada. The NLSCY sample is representative

of children aged 0–11 years who were living in any

Canadian province in 1994–1995, when survey weights

are applied. A full description of the NLSCY and its sam-

pling design is available elsewhere (Human Resources

Development Canada & Statistics Canada, 1995). Data

were accessed with permission from the Social Sciences

and Humanities Research Council of Canada.

The current study used data from the original longitu-

dinal cohort of the NLSCY, a sample that was 0–11 years

old at initial recruitment in 1994–1995. Data collection

occurred every 2 years, with eight collection cycles.

Using a cross-sectional design, data were included from

Cycle 4 (2000–2001) and Cycle 7 (2006–2007) to measure

all participants from the original cohort during adolescence

(between 12 and 17 years old). In Cycle 4, we included

5,580 adolescents who were 6–11 years old at initial re-

cruitment in 1994. In Cycle 7, we included 6,319 adoles-

cents who were 0–5 years old at initial recruitment in

1994.

Data collection for the NLSCY was completed via com-

puter-assisted telephone interviews and paper-and-pencil

questionnaires. Data collection methods for SES and

health variables are noted in the sections below. The

‘‘person most knowledgeable’’ was the youth’s biological

mother (90%) or biological father (8%) and will hereafter

be referred to as ‘‘parent.’’

Individual/Family SES Characteristics

Family SES information was collected by phone interviews

with the parent and their spouse. Household income (before

taxes and transfers) from all sources of income for all family

members during the previous 12 months was derived from

open-ended interview questions. Parental education (years)

was derived from questions about the highest level of ed-

ucation attained for parent and spouse. Mean years of ed-

ucation between the two parents was calculated (except in

cases where there was no spouse).

Province Income and Income Inequality

Income measures for each Canadian province were drawn

from the Canadian Socio-economic Information

Management System database from the Income Statistics

Division of Statistics Canada. Income inequality was mea-

sured using the Gini index, a measure of inequality that

ranges from 0 (perfect equality) to 1 (perfect inequality),

based on household income after taxes and transfers, ad-

justed for household size (Statistics Canada, 2013a). Mean

income was measured as the average household income

after taxes and transfers, adjusted for household size

(Statistics Canada, 2013b). Data from 2000 and 2006

were extracted to match the years of NLSCY data collec-

tion. Thus, we included information from the 10 Canadian

provinces from two different time points. Gini indices by

province and year are presented in Table I.

Health Outcomes

Health outcomes were broadly categorized into five catego-

ries: self-rated health, mental health, health behaviors, sub-

stance use behaviors, and physical health. All health

outcomes were coded such that higher scores indicate

worse health.

Self-Rated Health

Adolescents rated their health status as ‘‘excellent,’’ ‘‘very

good,’’ ‘‘good,’’ ‘‘fair,’’ or ‘‘poor’’ via self-completed

questionnaires (12–15 years) or telephone interviews

(16–17 years).

Table I. Gini Index by Province and Year

Province

Gini index

2000 2006

Alberta .312 .314

British Columbia .312 .319

Manitoba .290 .304

New Brunswick .291 .293

Newfoundland .302 .299

Nova Scotia .295 .295

Ontario .325 .320

Prince Edward Island .285 .265

Quebec .294 .291

Saskatchewan .295 .323

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Mental Health

Mental health was assessed via adolescent self-completed

paper questionnaires (12–15 years); items were aggregated

to form indices. For older adolescents (16–17 years), ag-

gregated indices were derived from the previous cycle of

data collection (i.e., when they were 14–15 years old). Self-

esteem was measured by four items taken from the General

Self Scale of the Marsh Self-Description Questionnaire

(Cronbach’s a¼ .73). Adolescents completed the

‘‘Behaviour Checklist,’’ which was factor analyzed by

Statistics Canada to identify six factors: indirect aggression

(5 items; a¼ .73–.74), physical aggression (6 items;

a¼ .74–.82), emotional disorder (7 items; a¼ .76–.79), hy-

peractivity/inattention (7 items; a¼ .75–.79), prosocial

behavior (10 items; a¼ .77–.88), and property offenses (6

items; a¼ .67–.77). These Cronbach’s a ranges are pre-

sented for Cycles 4 and 7 of the NLSCY.

Health Behaviors

Health behaviors were assessed via self-completed ques-

tionnaires for adolescents aged 12–15 years and via tele-

phone interviews for adolescents aged 16–17 years.

Television watching was derived from adolescent report of

average number of hours spent watching TV or videos or

playing video games per day. Response categories were

recoded to create a continuous variable using the median

value, where applicable. Physical activity was derived from

adolescents’ responses to two questions about frequency of

playing sports or doing physical activities during the week,

with or without a coach or instructor. Responses were

summed to create a total score. Breakfast eating was derived

from adolescent report of frequency of eating breakfast

from Monday to Friday.

Substance Use Behaviors

Substance use behaviors were assessed via self-completed

paper questionnaires for all adolescents. Alcohol use was

measured by adolescent report of their experience with

alcohol, ranging from ‘‘I have never had a drink of alcohol’’

to ‘‘About 6–7 days a week.’’ Cigarette use was measured

by adolescent report of their experience with smoking cig-

arettes from ‘‘I have never smoked’’ to ‘‘About 6–7 days a

week.’’

Physical Health

Limiting conditions, injuries, and chronic conditions were

assessed via parent telephone interviews for adolescents

aged 12–15 years and via adolescent telephone interviews

for adolescents aged 16–17 years. Limiting condition was

measured by report of a physical or mental condition or

health problem that reduces the amount or kind of activity

the adolescent can do (‘‘yes’’ or ‘‘no’’). Responses were

summed across three domains: home, school, and leisure

activities. Injuries were measured by report of an injury

requiring medical attention in the past 12 months (‘‘yes’’

or ‘‘no’’). Chronic conditions were measured by report of a

health professional diagnosis of the following long-term

conditions: asthma, bronchitis, food allergies, respiratory

allergies, other allergies, heart condition, kidney condition,

epilepsy, cerebral palsy, mental handicap, learning disabil-

ity, attention deficit/hyperactivity disorder, psychological

disorder, or other (‘‘yes’’ or ‘‘no’’). Responses were

summed to create a total score. General symptoms and

sleep difficulties were assessed via self-completed paper

questionnaires for adolescents aged 12–15 years and via

telephone interviews for adolescents aged 16–17 years.

General symptoms were derived from adolescent report of

frequency of occurrence of headaches, stomachaches, and

backaches in the past 6 months from ‘‘seldom or never’’ to

‘‘most days.’’ Responses were summed to create a total

score. Sleep difficulties were measured by adolescent

report of how often they had difficulties in getting to

sleep in the past 6 months from ‘‘seldom or never’’ to

‘‘most days.’’ Body mass index (kg/m2) was derived from

self-reported height and weight via a paper questionnaire

for all adolescents.

Missing Data

Longitudinal response rate for the NLSCY was 68% in

Cycle 4 and 57% in Cycle 7. We were unable to include

data for adolescents who did not participate in these cycles.

Multiple imputation (five data sets) was performed using

SAS (version 9.2) to impute missing information for partial

nonresponse data. Multiple imputation is preferable to

listwise deletion of data, as it retains information to in-

crease power and reduce bias (Enders, 2011). To impute

health outcomes, we included all other health outcomes

along with age, sex, cycle, and province in the imputation

model. To impute household income and parental educa-

tion, we included these variables along with parental em-

ployment status, family size, single parent status, number

of bedrooms in the home, and type of dwelling. Results

were largely identical when analyses were run on the orig-

inal versus imputed data set; therefore, only results based

on the imputed dataset are presented. The characteristics

of the current study sample are provided in Table II.

Analytical Strategy

Multilevel modeling techniques (Bryk & Raudenbush,

1987) were used to fit regression models to the nested

data. A two-level model was specified in which participants

(Level 1) were nested within province year (Level 2). The

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Level 1 model describes the effect of individual socioeco-

nomic variables, and the Level 2 model describes the effect

of province socioeconomic variables. Multilevel models

were specified using HLM 6.2 software.

To test the effect of income inequality, we entered

province income inequality as a Level 2 predictor while

controlling for Level 2 province mean income and Level

1 household income and parental education. To examine

whether provincial income inequality moderated the effect

of family SES on health, we tested cross-level interactions

of Gini index and household income, and Gini index and

parental education, while controlling for provincial mean

income.

Results

Gini coefficients by province and year are presented in

Table I. The lowest Gini coefficient was .265 (Prince

Edward Island in 2006), which is similar to the level of

income inequality in Finland in 2000 (.269) or Belarus in

2011 (.265). The highest Gini coefficient was .325

(Ontario in 2000), which is similar to the level of income

inequality in France in 2008 (.327) or Bangladesh in 2010

(.321). International Gini coefficients were obtained from

the World Bank (2014). Using the categories of low

(.244–.284), medium (.290–.354), and high (.355–.456)

from Elgar et al. (2005), most Canadian provinces fall

within a ‘‘medium’’ level of income inequality, as does

the Canadian mean level of inequality.

Descriptive sample characteristics for the 11,899 ado-

lescents included in the study are presented in Table II.

Cohort effects were not observed; thus, sample character-

istics are presented for the entire sample. Overall, the

sample was evenly divided across age and sex categories.

Mean parental education was about 13 years, which corre-

sponds to completion of secondary education or 1 year of

postsecondary education, depending on the Canadian

province. Mean pretax household income before taxes

was about $77,000, which is similar to national averages.

Descriptive statistics for health outcomes are presented in

Table III.

We hypothesized that greater provincial income in-

equality would be associated with worse health outcomes.

Results (presented in Table IV) indicated that greater

income inequality (higher Gini index) was associated

with more injuries requiring medical attention, more gen-

eral physical symptoms, and more life domains affected by

limiting conditions, after controlling for provincial mean

income, household income, and parental education.

We also hypothesized that associations between family

SES and health would be stronger in provinces with greater

income inequality. Cross-level interactions of income in-

equality with household income and parental education

are presented in Table V. Results indicated that greater

income inequality was associated with stronger associa-

tions for household income with limiting conditions, and

for parental education with limiting conditions, hyperactiv-

ity/inattention, and property offenses. In contrast, greater

income inequality was associated with a weaker association

for household income with cigarette use. Selected signifi-

cant interaction effects are illustrated in Figure 1; income

inequality tertiles were created for interpretation.

Discussion

Using a within-country design in Canadian adolescents,

the aim of the current study was to examine the indepen-

dent effects of income inequality, after accounting for mean

income and family SES, on multiple domains of adolescent

health. We tested for a main effect of provincial income

inequality on adolescent health and for a moderating effect

Table II. Sample Characteristics

Characteristic Mean (SD) N (%)

Age (in years) 14.33 (1.71)

12 2,229 (18.7)

13 2,321 (19.5)

14 1,927 (16.5)

15 1,857 (15.6)

16 1,855 (15.6)

17 1,710 (14.4)

Sex

Male 5,983 (50.3)

Female 5,916 (49.7)

Parental education (years) 13.10 (2.14)

Household income ($Canadian) 77,024 (55,433)

Cycle

4 (2000/2001) 5,580 (46.9)

7 (2006/2007) 6,319 (53.1)

Province

Alberta 1,253 (10.5)

British Columbia 988 (8.3)

Manitoba 912 (7.7)

New Brunswick 699 (5.8)

Newfoundland and Labrador 646 (5.5)

Nova Scotia 843 (7.1)

Ontario 2,993 (25.1)

Quebec 2,267 (19.1)

Prince Edward Island 349 (3.0)

Saskatchewan 949 (8.0)

Province-Level Income Inequality and Health Outcomes 5

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of provincial income inequality on associations between

family SES and adolescent health.

The first hypothesis was that greater provincial income

inequality would be associated with worse health outcomes

in adolescents. A significant association between income

inequality and poor health was observed for certain phys-

ical health outcomes, which provides limited support for

this hypothesis. Greater income inequality was related to

more injuries requiring medical attention, more frequent

physical symptoms like headaches, stomachaches, and

backaches, and more limitations at home, school, and

leisure due to a physical or emotional condition, after

controlling for family SES and mean province income.

However, provincial income inequality was not associated

with self-rated health, health behaviors like diet, physical

activity, or substance use, or on mental health problems

such as hyperactivity/inattention, emotional problems, or

aggression.

Previous research on the effects of income inequality

on health in adolescents has shown mixed results across

studies and outcomes. Greater country income inequality

was associated with poorer self-rated health in adolescents

(Torsheim et al., 2006), and greater state income inequality

was associated with higher obesity prevalence and lower

physical activity levels (Singh et al., 2008, 2009). In con-

trast, the current study did not observe significant associ-

ations between province income inequality and self-rated

health, body mass index, or physical activity. Of note, the

previous studies did not adequately control for average

income levels, which may be an important confound of

the effects of income inequality, while we included mean

province income as a covariate, along with household

income and parental education. The lack of significant

findings in the current study may be due in part to the

limited range of income inequality among Canadian prov-

inces, while previous studies have examined across

countries and states with more variation in level of

income inequality. Other factors that may contribute to

the differences in findings are the scale of the study (be-

tween country vs. within country), overall level of income

inequality in the country (high inequality in the United

States vs. medium inequality in Canada), and measure-

ment differences (self-report vs. measured, change in

methods of assessment). Based on current and previous

findings, independent effects of income inequality on ad-

olescent health are not consistently observed. However,

when significant associations are observed, they indicate

that greater income inequality is associated with poorer

health in adolescents.

The second hypothesis was that greater provincial

income inequality would be associated with steeper socio-

economic gradients in health. A significant cross-level in-

teraction between income inequality and family SES was

observed for limiting conditions, hyperactivity/inattention,

and property offenses in the expected direction, which

provides partial support for this hypothesis. Levin et al.

(2011) also observed a significant interaction between

Gini index and individual SES (as measured by the

Family Affluence Scale), which indicated that as country

Table III. Descriptive Statistics

Health outcome Mean (SD) N (%)

Self-rated health (1–5) 1.93 (0.80)

Excellent (1) 3,717 (31.2)

Very good (2) 5,798 (48.7)

Good (3) 1,970 (16.6)

Fair (4) 361 (3.0)

Poor (5) 53 (0.4)

Injury (past 12 months; 0–1)

No (0) 9,675 (81.3)

Yes (1) 2,224 (18.7)

Chronic conditions (number; 0–14) 0.63 (0.97)

Sleep difficulties (1–5) 2.19 (1.22)

Never (1) 4,426 (37.2)

Once per month (2) 3,474 (29.2)

Once per week (3) 2,152 (18.1)

Two or more time per week (4) 1,010 (8.5)

Most days (5) 837 (7.0)

General symptoms score (3–15) 5.79 (2.32)

Body mass index 21.51 (3.62)

Limiting condition

(number of domains: 0–3)

0.18 (0.62)

0 10,751 (90.4)

1 507 (4.3)

2 271 (2.3)

3 370 (3.1)

Physical activity score (2–8) 4.76 (1.64)

Television watching (hr/day) 2.49 (1.66)

Breakfast eating (1–4) 1.88 (1.04)

Every day (1) 5,950 (50.0)

3–4 days per week (2) 2,839 (23.9)

1–2 days per week (3) 1,739 (14.6)

Never (4) 1,371 (11.5)

Cigarette use score (1–8) 2.09 (1.90)

Alcohol use score (1–9) 3.28 (2.06)

Self-esteem score (0–16) 4.17 (2.50)

Indirect aggression score (0–10) 1.35 (1.55)

Emotional problems score (0–16) 3.45 (2.70)

Physical aggression score (0–12) 1.10 (1.64)

Hyperactivity/inattention score (0–16) 4.00 (2.68)

Prosocial behavior score (0–20) 8.76 (3.76)

Property offenses score (0–12) 1.02 (1.36)

Note. For all health behaviors and conditions, a lower score indicates better

health.

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Table IV. Main Effects of Province and Family SES on Health Outcomes

Province (Level 2) Individual/family (Level1)

Health outcomeGini index Mean income Household income Parent education

b 95% CI b 95% CI b 95% CI b 95% CI

Self-rated health .007 �0.04, 0.06 .018 �0.01, 0.05 �.061 �0.09, �0.03 �.062 �0.08, �0.04

Injuries .049 0.02, 0.08 �.024 �0.06, 0.02 .002 �0.02, 0.02 .027 0.01, 0.05

Chronic conditions .013 �0.05, 0.08 �.008 �0.05, 0.07 �.036 �0.06, �0.02 .001 �0.02, 0.02

Sleep difficulties �.042 �0.09, 0.01 .095 0.05, 0.14 �.026 �0.05, �0.01 .037 0.02, 0.06

General symptoms .048 0.002, 0.09 �.017 �0.06, 0.02 �.015 �0.03, 0.004 �.012 �0.03, 0.01

Body mass index �.035 �0.08, 0.01 .005 �0.03, 0.04 �.028 �0.05, �0.01 �.071 �0.09, �0.05

Limiting conditions .047 0.01, 0.09 .024 �0.01, 0.06 �.033 �0.05, �0.01 �.042 �0.06, �0.02

Low physical activity �.015 �0.07, 0.03 .002 �0.05, 0.05 �.074 �0.09, �0.06 �.100 �0.12, �0.08

Television hours .042 �0.01, 0.09 �.096 �0.15, �0.04 �.034 �0.05, �0.01 �.112 �0.13, �0.09

Low breakfast eating .012 �0.07, 0.09 .001 �0.08, 0.08 �.053 �0.07, �0.03 �.098 �0.12, �0.08

Cigarette use .048 �0.03, 0.13 �.102 �0.18, �0.02 �.038 �0.06, �0.02 �.085 �0.10, �0.06

Alcohol use .038 �0.03, 0.10 �.025 �0.09, 0.04 .022 0.01, 0.04 �.028 �0.04, �0.01

Low self-esteem �.020 �0.06, 0.02 .040 0.01, 0.07 �.058 �0.08, �0.04 �.031 �0.05, �0.01

Indirect aggression .022 �0.01, 0.05 �.012 �0.05, 0.03 �.002 �0.02, 0.01 �.029 �0.05, �0.01

Emotional problems .028 �0.02, 0.07 .013 �0.03, 0.05 �.041 �0.06, �0.02 �.001 �0.02, 0.02

Physical aggression .001 �0.06, 0.06 .046 �0.01, 0.11 �.032 �0.05, �0.01 �.081 �0.10, �0.06

Hyperactive/inattention �.005 �0.05, 0.05 .043 �0.01, 0.09 �.028 �0.05, �0.01 �.051 �0.07, �0.03

Prosocial behavior �.021 �0.06, 0.02 .018 �0.02, �0.06 �.037 �0.06, �0.02 �.038 �0.06, �0.02

Property offenses �.013 �0.06, 0.04 .040 �.0.01, 0.09 �.031 �0.05, �0.01 �.031 �0.05, �0.01

Expected direction Positive Negative Negative Negative

Note. Standardized b coefficients and 95% confidence intervals are presented. Bold values are statistically significant at p < .05. All models include age, sex, parental educa-

tion, household income, Gini index, and mean income.

Table V. Cross-Level Interaction of Gini Index With Household Income and Parental Education

Health outcomeGini�Household income Gini�Parental education

b 95% CI b 95% CI

Self-rated health .010 �0.02, 0.04 �.011 �0.03, 0.01

Injuries �.005 �0.03, 0.02 .001 �0.02, 0.02

Chronic conditions .006 �0.01, 0.03 .009 �0.01, 0.03

Sleep difficulties �.005 �0.03, 0.02 �.008 �0.03, 0.01

General symptoms �.006 �0.03, 0.02 �.006 �0.03, 0.01

Body mass index .011 �0.01, 0.03 .011 �0.01, 0.03

Limiting conditions �.022 �0.04, �0.004 �.037 �0.06, �0.02

Low physical activity .020 �0.01, 0.05 .000 �0.02, 0.02

Television hours .005 �0.02, 0.03 .003 �0.02, 0.02

Low breakfast eating .012 �0.01, 0.03 �.001 �0.02, 0.02

Cigarette use .029 0.01, 0.05 .019 0.00, 0.04

Alcohol use .002 �0.02, 0.02 �.002 �0.02, 0.02

Low self-esteem .002 �0.03, 0.03 �.006 �0.03, 0.01

Indirect aggression �.008 �0.03, 0.01 �.013 �0.03, 0.01

Emotional problems �.004 �0.02, 0.02 �.017 �0.04, 0.002

Physical aggression .003 �0.03, 0.03 �.023 �0.04. 0.001

Hyperactivity/inattention �.003 �0.02, 0.02 �.024 �.0.04, �0.004

Prosocial behavior �.013 �0.04, 0.02 �.009 �0.03, 0.01

Property offenses �.003 �0.02, 0.02 �.023 �0.04, �0.004

Expected direction Negative Negative

Note. For interaction terms, standardized b coefficients and 95% confidence intervals are presented. Bold values are statistically significant at

p < .05. Gini� Income models control for age, sex, mean province income, Gini index, and household income. Gini� Education models control

for age, sex, mean income, Gini index, and parental education.

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income inequality increases, the socioeconomic gradient in

life satisfaction increased. In the present study, income

inequality displayed a main effect on limiting conditions,

as well as a moderating effect on the family socioeconomic

gradients for this outcome. Moreover, steeper gradients

were observed in more unequal provinces for two ‘‘exter-

nalizing’’ mental health issues: hyperactivity and property

offenses. In other words, low family SES was most strongly

linked to externalizing problems in more unequal prov-

inces. Previous research has linked income inequality to

juvenile homicide and bullying (Wilkinson & Pickett,

2007). For cigarette use, we observed that individual so-

cioeconomic gradients decreased as income inequality in-

creased. This finding may be linked to regional variations in

youth cigarette use across Canada (Reid & Hammond,

2009), which may confound the associations. For instance,

youth smoking rates are much higher in Quebec compared

with other provinces; thus, a socioeconomic gradient may

be less apparent in this province.

The current study did not evaluate pathways directly;

however, these results may have implications for the two

main proposed pathways between income inequality and

health. The social cohesion pathway considers the impor-

tance of psychological processes of social trust and social

comparisons. Thus, this pathway may be more directly

linked to mental health outcomes. In the current study,

we found that steeper family SES gradients existed for in-

attention/hyperactivity and property offenses in more un-

equal provinces. Crime and violence may be uniquely

linked to income inequality through lower social trust, in-

creased importance on status, and increased sensitivity of

shame and humiliation (Wilkinson & Pickett, 2009).

Associations between income inequality and internalizing

mental health issues, such as self-esteem and emotional

problems, were not observed, which suggests that stressful

social comparisons may not explain associations between

provincial income inequality and adolescent health in

Canada. The policy pathway considers the importance of

social, education, and health policies. For example, differ-

ential provision of special education services across

Canadian provinces may influence the degree of limitation

a child with a disability faces. Funding of and access to

primary health care, which vary across Canadian provinces,

may affect general physical symptoms like stomachaches or

headaches. Similarly, differences in bicycle helmet legisla-

tion across Canadian provinces have been linked to injuries

(MacPherson et al., 2002). Further research is required to

investigate these associations.

Although not the primary aim of the current study, it

is important to note that higher family SES was associated

with better adolescent health for most of the health out-

comes and health behaviors that were measured. Even after

accounting for provincial income and income inequality,

strong and consistent socioeconomic gradients were ob-

served for Canadian adolescents. This suggests that more

proximal socioeconomic indicators (household income and

parent education) had stronger and more consistent asso-

ciations with adolescent health than distal socioeconomic

indicators (provincial income, provincial income inequal-

ity), which has both theoretical and policy-related

implications.

This article adds to the literature that has used a

multilevel design to examine associations between

income inequality and health during adolescence. One of

the strengths of the current study was our ability to exam-

ine the independent effects of income inequality, while

statistically controlling for mean income, and parent-re-

ported household income and parental education. This

study tested within-country associations between income

inequality and adolescent health in Canada, a country with

Figure 1. Effects of parental education on (a) hyperactivity/inattention and (b) limiting conditions are presented by income inequality tertiles

(low, medium, and high).

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medium-level income inequality, which was important

given the evidence that within-country effects of income

inequality may exist only in highly unequal societies.

Finally, we were able to examine the effects of income in-

equality in a broad range of health outcomes and health

behaviors, which allowed for a more thorough investigation

of these associations in adolescence.

There are several methodological limitations of the cur-

rent study. First, the amount of variability in income inequal-

ity between Canadian provinces is limited compared with

previous cross-country analyses, which may contribute to

the lack of significant associations in the current study. A

previous meta-analysis of adult findings noted weaker asso-

ciations in within-country comparisons compared with be-

tween-country comparisons (Kondo et al., 2009). Second,

although we examined associations in both 2000 and 2006

to increase our statistical power, we used a cross-sectional

design and are not able to determine the direction of the

observed associations. Third, the NLSCY relies on adoles-

cent and parent reports of health behaviors and health out-

comes, which are subject to differences in response styles

and are a potential source of bias. Moreover, the method of

assessing certain variables changed at age 16 years (parent

report to self-report, paper questionnaire to telephone inter-

view), which introduces additional measurement error and

potential for bias. Fourth, the current study aimed to provide

an overview of the associations between income inequality

and a range of adolescent health outcomes. Thus, many of

the health outcomes are not examined in great depth or

detail, and statistical bias is possible given that multiple

health outcomes were tested. Replication of these results,

focusing on specific health outcomes, is recommended.

Fifth, although we used after-tax income to derive the Gini

coefficient, in line with previous studies (Torsheim et al.,

2006), the NLSCY data set included before-tax household

income only. Finally, although the original sample was rep-

resentative of the Canadian population at initial recruitment,

significant attrition occurred over time in the NLSCY. To

maximize available data, we used multiple imputation to

examine associations in all remaining participants.

Future research in this area may address some of the

limitations of the current study, as well as further the un-

derstanding of the association between income inequality

and health. Studies that link to health records may help to

reduce bias associated with self-reported health variables.

In addition, further examination of age and developmental

influences on associations between income inequality and

health during adolescence will further conceptual under-

standing. Further, longitudinal study designs that docu-

ment changes in income equality and subsequent

changes in health will help to determine the directionality

of these associations. Moreover, longitudinal data are re-

quired to test the mediational pathways between income

inequality and adolescent health. For instance, social com-

parison or social cohesion may be measured as a mediating

pathway between income inequality and health outcomes,

particularly limiting conditions, injuries, general symp-

toms, and mental health. Additionally, specific policies or

programs that are offered differentially across provinces or

countries, such as day-care policies, special education ser-

vices, access to primary health care, or access to mental

health services, may be examined as a mediating pathway

between income inequality and adolescent health out-

comes that have shown significant associations in the cur-

rent study or previous studies.

In conclusion, this study provided limited evidence for

independent associations between provincial income in-

equality and health in Canadian adolescents. We observed

a main effect of income inequality for some adolescent

physical health outcomes, and a moderating effect on

associations between parental education and adolescent

externalizing mental health. Using a multilevel, within-

country design in Canada, we found that provincial

income inequality was not related to most adolescent

health outcomes, including self-rated health, health and

substance use behaviors, and internalizing mental health

problems. Further understanding of the effects of income

inequality on health in childhood and adolescence, as well

as adulthood, will help us to promote interventions to

reduce inequality or its impact on health and well-being.

Acknowledgments

This analysis was based on the Statistics Canada master

files NLSCY Cycles 4 and 7, which contain anonymized

data collected from 1994 to 2007. The responsibility for

the use and interpretation of these data is solely that of the

authors. The opinions expressed in this article are those of

the authors and do not represent the view of Statistics

Canada. The authors extend their sincere thanks to

members of the International Network for Research in

Inequalities in Child Health (INRICH).

Funding

This work was supported by funding from the Canadian

Institutes of Health Research (J. McGrath OCO-79897,

MOP-89886, MSH-95353, MOP-123533; E. Quon CGM-

89256) and Quebec Inter-University Centre for Social

Statistics.

Conflicts of interest: None declared.

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