Relative deprivation and incident functional disability
among older Japanese women and men: prospective
cohort study
N Kondo,1,2 I Kawachi,1 H Hirai,3 K Kondo,3 S V Subramanian,1 T Hanibuchi,3,4
Z Yamagata1
c Additional table published

online only at http://jech.bmj.
com/content/vol63/issue6
1

Department of Society, Human
Development, and Health,Harvard School of Public Health,Boston, USA; 2 Department of
Health Sciences,
Interdisciplinary Graduate Schoolof Medicine and Engineering,
University of Yamanashi, Chuoshi, Japan; 3 Research
Promotion Center for Community
Care, Nihon Fukushi University,
Nagoya-shi, Japan; 4 Institute ofRegional Studies, Osaka
University of Commerce, Higashi
Osaka-shi, Japan
Correspondence to:
Dr N Kondo, Department of
Health Sciences,
Interdisciplinary Graduate Schoolof Medicine and Engineering,
University of Yamanashi,
Shimokato 1110, Chuo-shi,
Yamanashi 409-3898, Japan;
nkondo@yamanashi.ac.jp
Accepted 2 December 2008

This paper is freely available
online under the BMJ Journals
unlocked scheme, see http://
jech.bmj.com/info/unlocked.dtl

ABSTRACT
Background: A prospective observational study was
conducted to test the hypothesis that relative deprivation
was associated with incident physical or cognitive
disability, independent of absolute income.
Methods: Study subjects consist of 9463 non-disabled
people aged 65+ years in the Aichi Gerontological
Evaluation Study (AGES), Aichi prefecture, Japan.
Baseline mail-in survey in 2003 gathered information on
income, educational attainment, lifestyle factors (smoking, alcohol consumption and health check-up) andhealthcare utilisation. Three-year incidence of disability
was assessed through public long-term care insurance
databases and resident registry.
Results: A total of 7673 subjects (81%) with complete
information were analysed. Our measure of relative
deprivation was the Yitzhaki index across eight referencegroups, which calculates the deprivation suffered by eachindividual as a function of the aggregate income shortfall
for each person relative to everyone else with higher
incomes in that person’s reference group. Cox regression
demonstrated that, after controlling for sociodemographic
factors (including absolute income), the hazard ratio (and
95% confidence intervals) of incident physical/cognitive
disability per one standard deviation increase in relative
deprivation ranged from 1.13 (0.99 to 1.29) to 1.15 (1.01
to 1.31) in men and from 1.11 (0.94 to 1.31) to 1.18 (1.00
to 1.39) in women, depending on the definition of thereference group. Additional adjustment for lifestyle factors
attenuated the hazard ratios to statistical non-significance.
Conclusion: Relative deprivation may be a mechanism
underlying the link between income inequality anddisability in older age, at least among men. Lifestylefactors in part explain the association between relative
deprivation and incident disability.

Population ageing in developed countries has
spurred political concerns about future impacts ofdisability on health services utilisation, and many
countries have drafted public health measures toaddress long-term care (LTC) prevention.1 For
example, Japan established public LTC insurance
in 2000, which places strong emphasis on individual behavioural changes.2 3 To improve theperformance of LTC prevention policies, it is also
critical to understand and address the social
determinants of LTC need such as income, education4 and income inequality.5 6
Although still controversial, the association
between income inequality and health has been
examined in a wide range of countries andJ Epidemiol Community Health 2009;63:461–467. doi:10.1136/jech.2008.078642

settings.5 6 Two distinct hypotheses have been
proposed through which income inequality is
believed to affect health at the individual level.
First, the absolute income hypothesis posits thatan unequal society creates more people in poverty
who suffer poor health due to material insufficiency.4 Second, the relative deprivation hypothesis
posits that the degree of income inequality insociety will heighten an individual’s sense of
relative deprivation, resulting in frustration,
shame, stress and maladaptive coping responses(such as smoking).7 8 The theory of social comparison underlies this hypothesis.9 Empirical support
for this hypothesis has been provided recently bystudies in the Nordic countries,10 11 the UnitedStates12 13 and Japan,14 although negative studies
have also been reported.15–17 However, these studies
all used data in working-age populations, andevidence among the elderly remains sparse.
In this study, we sought to provide a test of therelationship between relative deprivation and thefuture onset of functional disability among older
Japanese individuals.

METHODS
Study population
We used data from the Aichi Gerontological
Evaluation Study (AGES), a prospective longitudinal study aimed at clarifying the role ofcontextual and psychosocial factors on the healthand longevity of older adults. We conducted abaseline survey in November 2003 in a random
sample of functionally independent 59 622 individuals aged 65 years or older residing in 15
municipalities from three prefectures in Japan.
The sample was restricted to those who were notalready receiving the public LTC insurance
benefit. Subjects were included only if theyreported no limitations in basic activities of dailyliving including walking, bathing and toilet use.18
The mail-in questionnaire also enquired aboutsociodemographic and lifestyle factors, that isage, gender, marital status, income, education,smoking habits, alcohol consumption, having ahealth check-up or not in the last few years andhealth status including medical care utilisation. A
total of 32 891 subjects returned the questionnaire. Baseline characteristics of the participants
have been reported elsewhere.19 20 The AGES
protocol was approved by the ethics committee
in Research of Human Subjects at Nihon Fukushi
University.
461

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Research reportIncident functional disability
We followed the subjects in terms of the onset of physical or
cognitive disability by using the public LTC insurance databasemaintained by each participating municipality. We determinedfunctional disability based on new registration in the public
LTC insurance data base, that is when a person newly qualified
for the insurance benefit.21 The qualification was based on astandardised multistep assessment of functional and cognitive
impairment including a physician’s standardised examination.2
These criteria for determining the onset of disability have beenused in previous epidemiological studies and also form the basisof health need assessment by Japanese local governments.22 23
We also included mortality as an endpoint, certified by the local
registry. As of the end of October 2006, we linked the baseline
data of all 9463 participants living in the five participating
municipalities in Aichi prefecture to the LTC insurance
database. Of those, 7673 subjects (81%) provided complete
baseline key information. People who did not provide thecomplete information were 26% more likely to be female, andon average 2.2 years older than those who provided theinformation. The LTC insurance data from the remaining 10municipalities were not available for reasons such as delay indata handling or clerical procedures in the municipalities.

Income and relative deprivation
The baseline survey asked about annual household pre-tax
income in 2002. The income question had 14 categories, and the
midpoints were set as household income in each category. The
incomes for people in the top-coded category were obtained by
Pareto estimation.24 We adjusted household income for household size, dividing the income by the square root of the numberof people in that household.
Following the recently adopted method of Eibner andcolleagues,12 13 relative deprivation was operationalised in thepresent study using the Yitzhaki index,25 which is itself based on
the theory of relative deprivation articulated earlier by
Runciman.26 In brief, relative deprivation for each individual iscalculated as the aggregated shortfall in income between that
individual and everyone else with higher incomes in that
person’s reference group:

where the amount of relative deprivation for individual i is thesum of the income gap between individuals i and j (yj – yi, where
j has higher income than i) divided by the total number ofpeople in the reference group (N). As we cannot know thereference group for each individual (ie, to whom each personcompares him/herself), our approach is to fit alternative
definitions of reference groups: others living in the samegeographical area (five municipalities), others in the same agegroup (65–74 or 75+ years old) or gender, others with the sameeducational attainment (0–9 or 9+ years of education). We also
created reference groups defined by the combinations of thesevariables. Each reference group ranged from 1307 to 5364
subjects when a single variable was used as the basis for social
comparison, and from 191 to 754 when three variables wereused.

Covariates
Other explanatory variables included age, gender, marital status(married, widowed or divorced, never married), educational462

attainment (less than 6 years, 6–9 years, 10–12 years or
13 years or longer) and medical care utilisation (no healthproblems, minor health problems not currently needing medicalcare, health problems needing but not currently receiving
medical care due to patient choice, or currently receiving
medical care). We also considered lifestyle factors including
smoking history (never, ever or current), alcohol consumption(non-drinker; not drink everyday; drink 35 g of alcohol or less;or drink more than 35 g every day) and receipt of health checkup (had check-up in the last year, had it in the last 2 or 3 years,
had it 4 years ago or before, or never had it).

Statistical analysis
Cox proportional hazard models were used to calculate thehazard ratio (HR) and 95% confidence intervals (CI) for
subsequent disability onset according to the level of relative
deprivation. Multivariate models were adjusted for absoluteincome and other covariates. All models were stratified bygender.27 We also modelled relative deprivation further adjusted
for lifestyle factors in order to assess whether such factors
mediated the association between relative deprivation and theonset of disability. To address potential multicollinearity
between relative deprivation and absolute income, we also
carried out analysis stratified by median absolute income. In our
primary analysis, both income and relative deprivation weretreated as continuous variables, and income was not equivalisedby household size because this approach minimised thecollinearity between the two variables. We subsequently
conducted a sensitivity analysis using alternative specificationsof both variables (ie, continuous and quartile). The utilisation ofequivalised rather than non-equivalised income as a covariate
did not materially alter the results or our conclusions. All
statistical analyses were performed using SAS statistical package
version 9.1 (SAS Institute Inc., Cary, NC, USA).

RESULTSOver 11 456 person–years of observation in men and 10 216
person–years in women, we observed 191 and 286 subjects
newly registered in the LTC insurance database, as well as 313
and 146 deaths respectively (total 504 and 432). The incidence
rate (IR) of functional disability (ie, new registration in the LTC
insurance database and mortality) was 0.044 in men and 0.042
in women. Participants who were older, unmarried or had lower
educational attainment showed higher IRs. Lower income wasassociated with higher IR among male participants, whereas theassociation was unclear among women. The IR also differed bylifestyle factors. Relative deprivation was positively associatedwith the IR regardless of the reference groups selected for
calculating the Yitzhaki index. Among men, the IR ranged from
0.031 to 0.036 in the lowest quartile and from 0.061 to 0.064 in
the highest quartile; while among women, the range was from
0.043 to 0.049 in the lowest and from 0.049 to 0.053 in thehighest quartile (table 1).
Survival analysis in men indicated a statistically significant
association between higher relative deprivation and incident
disability across the models based on alternative referencegroups (table 2). The HRs for incident disability ranged from1.19 to 1.26 per one standard deviation (SD) increase in relative
deprivation, depending on the definition of reference groups.
The HRs were attenuated but still statistically significant evenadjusting for absolute income, demographic factors and medicalcare utilisation (Model 1), except for the area/gender/age model(HR = 1.13, 95% CI 0.99 to 1.29). The adjusted HRs ranged
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Research reportTable 1 Baseline characteristics of the subjects and incidence rate of functional disability: the Aichi Gerontological Evaluation Study (AGES), Aichi,
Japan, 2003–2006
Men (4061 respondents)
Baseline characteristics

N

Incidence/person–year

Women (3612 respondents)
Incidence rate

Age (years)
65–74
2900
234/8368
0.028
75+
1161
270/3088
0.087
Marital status
Married3660
420/10 371
0.040
Divorced/separated
335
69/9080.076
Never married
22
4/58
0.069
Other
15
4/41
0.097
Household equivalised income* (ranges in million Japanese yen)
Quartile 1 (0.88–1.57)
809
139/2216
0.063
Quartile 2 (1.58–2.46)1118
129/3162
0.041
Quartile 3 (2.47–3.17)
992
123/2806
0.044
Quartile 4 (3.18–10.66)
1142
113/3272
0.035
Mean (SD)2.53 (1.35)
Educational attainment
9 years or less2225
312/6233
0.050
10+ years
1804
188/5136
0.037
Medical care utilisation
None (no health1198
89/3478
0.026
problems)
26/6620.039
Have health problems but 233
not have medical care bypatient choice
Have regular medical care 2505
375/6962
0.054
SmokingNever1104
136/3113
0.044
Ever
1900
243/5352
0.045
Current
944
107/2678
0.040
Alcohol consumption
None
1674
286/4588
0.062
Drink 35 g/day of alcohol 1976
180/5685
0.032
or less
Drink .35 g alcohol/day
364
30/1054
0.028
Health check-up
Yes: in last 2–3 years
2685
251/7695
0.033
Yes: 4+ years ago
597
111/1630
0.068
Never
684
117/1884
0.062
Relative deprivation defined by geographical area (municipality) of residence (ranges 61000)
Quartile 1 (0–284)
1039
99/2980
0.033
Quartile 2 (285–610)
1059
124/3014
0.041
Quartile 3 (611–1055)
1090
135/3063
0.044
Quartile 4 (1056–2579)
873
146/2400
0.061
Mean (SD)702 (534)
Relative deprivation defined by age group (ranges 61000)
Quartile 1 (0–274)
1053
93/3035
0.031
Quartile 2 (275–563)
1092
142/3076
0.046
Quartile 3 (564–1023)
1042
116/2956
0.039
Quartile 4 (1024–2370)
874
153/2389
0.064
Mean (SD)705 (534)
Relative deprivation defined by educational attainment (ranges 61000)
Quartile 1 (0–292)
1007
105/2880
0.036
Quartile 2 (293–631)
995
114/2828
0.040
Quartile 3 (632–1031)
1149
131/3256
0.040
Quartile 4 (1032–2706)
878
150/2405
0.062
Mean (SD)696 (521)

N

Incidence/person–year

Incidence rate

2464
1148

157/7167
275/3049

0.022
0.090

2205
1267
89
11

182/6357
228/3469
19/239
0/33

0.029
0.066
0.079
0.000

1032
873
729
978

152/2887
90/2494
66/2086
124/2750

0.053
0.036
0.032
0.045
2.38 (1.46)

2213
1364

276/6240
150/3881

0.044
0.039

907

68/2630

0.026

238

24/682

0.035

2314

324/6467

0.050

3317
98
82

388/9395
15/268
18/223

0.041
0.056
0.081

3104
446

392/8745
31/1296

0.045
0.024

2/19

0.104

2472
333
699

224/7114
43/939152/1850

0.031
0.046
0.082

871
835
848
1058

114/2437
75/2399
91/2415152/2965

0.047
0.031
0.038
0.051
813 (639)

916
788
839
1069

112/2577
79/2248
83/2403
158/2989

0.043
0.035
0.035
0.053
818 (642)

894
786
817
1080

122/2490
67/2265
88/2334
149/3031

0.049
0.030
0.038
0.049
789 (626)

7*100 yen = US$0.95 in September 2008.

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463

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Research reportTable 2 Crude and adjusted hazard ratios (95% confidence intervals)
for incident functional disability per one standard deviation (SD) increase
in relative deprivation: the Aichi Gerontological Evaluation Study (AGES),
Aichi, Japan, 2003–2006
Reference groupdefined by:
Men
Area
Age
Education
Area and sex
Age and sex
Education and sex
Area, sex and age
Area, sex andeducation
Women
Area
Age
Education
Area and sex
Age and sex
Education and sex
Area, sex and age
Area, sex andeducation

Crude

Model 1Model 2

1.23 (1.13 to 1.33) 1.14 (1.00 to 1.30) 1.09 (0.95 to 1.24)
1.26 (1.16 to 1.36) 1.14 (1.00 to 1.31) 1.09 (0.95 to 1.26)
1.19 (1.10 to 1.30) 1.15 (1.01 to 1.31) 1.09 (0.96 to 1.25)
1.23 (1.14 to 1.33) 1.14 (1.00 to 1.30) 1.09 (0.95 to 1.25)
1.22 (1.13 to 1.33) 1.14 (1.00 to 1.31) 1.09 (0.95 to 1.25)
1.19 (1.10 to 1.29) 1.15 (1.01 to 1.31) 1.09 (0.96 to 1.25)
1.21 (1.12 to 1.32) 1.13 (0.99 to 1.29) 1.08 (0.94 to 1.23)
1.19 (1.10 to 1.29) 1.14 (1.01 to 1.30) 1.09 (0.95 to 1.24)

1.07 (0.98 to 1.18) 1.12 (0.95 to 1.32) 1.07 (0.91 to 1.26)
1.10 (1.01 to 1.21) 1.18 (1.00 to 1.39) 1.12 (0.95 to 1.33)
1.07 (0.97 to 1.17) 1.16 (0.99 to 1.37) 1.11 (0.94 to 1.30)
1.07 (0.97 to 1.17) 1.11 (0.95 to 1.31) 1.06 (0.90 to 1.25)
1.14 (1.04 to 1.24) 1.18 (0.99 to 1.39) 1.12 (0.94 to 1.33)
1.07 (0.97 to 1.17) 1.16 (0.99 to 1.37) 1.11 (0.94 to 1.30)
1.12 (1.02 to 1.23) 1.11 (0.94 to 1.31) 1.06 (0.90 to 1.25)
1.06 (0.97 to 1.16) 1.14 (0.97 to 1.33) 1.08 (0.92 to 1.27)

Model 1 is adjusted for age, income, marital status, medical care utilisation andeducation. Model 2 is adjusted for the covariates in Model 1 plus smoking, alcohol
consumption and health check-up. Relative deprivations are calculated using
household equivalised income. Income as a covariate is not equivalised (in order tominimise multicollinearity between relative deprivation and income).

0.84 (0.76 to 0.92) in men, and became non-significant in Model
1 ranging from 0.95 (0.82 to 1.10) to 0.98 (0.84 to 1.13). The
crude HR among women was 1.02 (0.93 to 1.12) and ranged
from 1.09 (0.92 to 1.28) to 1.14 (0.97 to 1.34) in Model 1.
Stratified analyses by median income showed a stronger
association between relative deprivation and incident disability
among high-income men compared with low-income men(table 3). For example, the adjusted HRs (95% CI) per 1 SD
increase in the area model were 1.19 (1.04 to 1.36) and 1.89 (1.29
to 2.79) in the low- and high-income groups respectively.
Women showed no statistically significant HRs. Although thestratified models could still have non-negligible confounding ofincome, supplementary analysis stratified by tertiled income
showed that, among men, the HRs of relative deprivation wereconsistently elevated with two exceptions in the middle-income
strata in age and age/sex models. However, these HRs were notstatistically significant, most probably because of the smaller
number of incident disability cases in each stratum(Supplementary table).
In sensitivity analyses using alternative specifications ofincome (table 4), the adjusted HRs per 1 SD increment ofrelative deprivation (in the education model, adjusted forincome, demographic factors and medical care) were generally
higher than 1.13 whatever the specification of income variable(table 4). The adjusted HRs by relative deprivation increased
across increasing quartiles. Variance inflation factors were thelowest in the primary analysis (where both income and relative
deprivation were continuous).

DISCUSSION
from 1.13 to 1.15. When the models were further adjusted forlifestyle factors, the adjusted HRs were attenuated by 4–5% andwere not statistically significant (Model 2). In women, in
contrast, the multivariate models (Model 1) were statisticallysignificant only in the age model (HR = 1.18, 95% CI 1.00 to
1.39, which was attenuated to statistical non-significance after
additional adjustment for lifestyle factors (Model 2). In terms ofabsolute income, the crude HR (95% CI) per 1 SD increase was

Our 3-year prospective study is consistent with the relative
deprivation hypothesis in male though not in female Japaneseelderly. Our findings are consistent with studies from Nordic
countries and the United States, as well as our previous study inJapan.10–14 Eibner and Evans found the associations between
relative deprivation (measured by the Yitzhaki index) andincreased mortality, smoking and obesity in a cohort of over
500 000 US working-aged men.12 Another US study reported an

Table 3 Adjusted hazard ratios* (95% confidence intervals) for incident functional disability per one standard deviation (SD) increase in relative
deprivation by high and low absolute incomes separated by median: the Aichi Gerontological Evaluation Study (AGES), Aichi, Japan, 2003–2006(N = 7673)
Model 1
Reference group defined by:
Men
Area
Age
Education
Area and sex
Age and sex
Education and sex
Area, sex and age
Area, sex and education
Women
Area
Age
Education
Area and sex
Age and sex
Education and sex
Area, sex and age
Area, sex and education

Model 2

Low income

High income

Low income

High income

1.19 (1.04 to 1.36)
1.21 (1.06 to 1.38)
1.18 (1.04 to 1.35)
1.19 (1.04 to 1.36)
1.21 (1.06 to 1.38)
1.18 (1.04 to 1.35)
1.19 (1.04 to 1.36)
1.16 (1.02 to 1.32)

1.89 (1.29 to 2.79)
1.76 (1.19 to 2.62)
1.81 (1.25 to 2.63)
1.97 (1.32 to 2.95)
1.82 (1.19 to 2.76)
1.86 (1.26 to 2.72)
1.83 (1.23 to 2.71)
2.00 (1.38 to 2.89)

1.17 (1.02 to 1.33)
1.19 (1.04 to 1.36)
1.17 (1.02 to 1.33)
1.17 (1.02 to 1.34)
1.19 (1.04 to 1.36)
1.17 (1.02 to 1.33)
1.16 (1.02 to 1.33)
1.14 (1.00 to 1.30)

1.82 (1.24 to 2.68)
1.71 (1.15 to 2.54)
1.72 (1.19 to 2.50)
1.89 (1.26 to 2.83)
1.75 (1.15 to 2.66)
1.76 (1.20 to 2.58)
1.76 (1.19 to 2.62)
1.88 (1.30 to 2.72)

1.07 (0.92 to 1.24)
1.12 (0.96 to 1.31)
1.09 (0.94 to 1.28)
1.06 (0.91 to 1.24)
1.12 (0.96 to 1.32)
1.09 (0.94 to 1.28)
1.06 (0.91 to 1.23)
1.06 (0.91 to 1.23)

0.83 (0.48 to 1.41)
0.76 (0.45 to 1.27)
0.86 (0.52 to 1.43)
0.84 (0.50 to 1.39)
0.78 (0.49 to 1.25)
0.85 (0.52 to 1.39)
0.88 (0.56 to 1.40)
1.00 (0.62 to 1.61)

1.05 (0.90 to 1.23)
1.11 (0.95 to 1.30)
1.07 (0.92 to 1.25)
1.05 (0.90 to 1.22)
1.11 (0.94 to 1.30)
1.07 (0.92 to 1.25)
1.04 (0.89 to 1.22)
1.04 (0.89 to 1.21)

0.89 (0.52 to 1.51)
0.82 (0.49 to 1.38)
0.92 (0.55 to 1.52)
0.90 (0.54 to 1.48)
0.84 (0.53 to 1.35)
0.91 (0.56 to 1.48)
0.95 (0.60 to 1.50)
1.05 (0.66 to 1.68)

Model 1 is adjusted for age, marital status, medical care and education. Model 2 is adjusted for the covariates in Model 1 plus smoking, alcohol consumption and health check-up.

464

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Research reportTable 4 Sensitivity analysis by alternative specifications of relative deprivation and income: adjusted HRs (95% CI) for incident functional disability inmen: the Aichi Gerontological Evaluation Study (AGES), Aichi, Japan, 2003–2006
Variable specification (relative deprivation/income)Continuous/continuous(primary analysis)

Continuous/quartile

HR (95% CI)

HR (95% CI)

VIF

Relative deprivation defined by education
Continuous
1.15 (1.01 to 1.31)
2.66
Quartile 1 (least deprived)
Quartile 2
Quartile 3
Quartile 4
Absolute income
0.98 (0.84 to 1.13)
2.69
Continuous
Quartile 1
Quartile 2
Quartile 3
Quartile 4 (most affluent)
Relative deprivation defined by area of residence, sex and age
Continuous
1.13 (0.99 to 1.29)
2.70
Quartile 1 (least deprived)
Quartile 2
Quartile 3
Quartile 4
Absolute income
Continuous
0.95 (0.82 to 1.10)
2.59
Quartile 1
Quartile 2
Quartile 3
Quartile 4 (most affluent)

Quartile/continuous
VIF

HR (95% CI)

Quartile/quartile
VIF

HR (95% CI)

VIF

Reference
0.96 (0.68 to 1.34)
1.10 (0.73 to 1.64)
1.55 (0.94 to 2.54)

2.39
4.06
5.66

1.13 (0.96 to 1.33) 4.14
Reference
1.12 (0.78 to 1.59) 2.67
1.27 (0.83 to 1.93) 4.27
1.66 (1.02 to 2.72) 5.07
1.01 (0.84 to 1.21) 3.95
1.18 (0.70 to 2.00) 4.96
1.11 (0.78 to 1.57) 2.85
1.24 (0.96 to 1.60) 1.86
Reference

1.06 (0.63 to 1.80)
1.08 (0.70 to 1.65)
1.29 (0.93 to 1.79)
Reference

4.77
3.83
2.87

1.10 (0.93 to 1.30) 4.47
Reference
1.23 (0.88 to 1.71) 2.48
1.29 (0.89 to 1.87) 3.43
1.55 (0.99 to 2.42) 4.33

Reference
1.13 (0.82 to 1.54)
1.20 (0.84 to 1.70)
1.34 (0.86 to 2.08)

2.20
3.15
4.59

0.97 (0.83 to 1.14) 3.16
1.33 (0.79 to 2.23) 5.08
1.17 (0.82 to 1.65) 2.82
1.29 (1.00 to 1.67) 1.82
Reference

1.34 (0.84 to 2.13)
1.13 (0.78 to 1.63)
1.25 (0.93 to 1.66)
Reference

3.78
3.03
2.31

VIF, variance inflation factor; HR, hazard ratio; CI, confidence intervals. HRs of continuous variables are per one standard deviation increase. All models are adjusted for age, marital
status, medical care utilisation and education. Two models with the largest and smallest effect sizes of relative deprivation are selected for sensitivity analysis. VIFs higher than 10
are commonly considered to be problematic.

association between the Yitzhaki index and increased mental
health service utilisation.13 We also found a significant crosssectional association between the Yitzhaki index and poor selfrated health in a Japanese national sample.14 A Swedish study
found an association between relative deprivation and poor selfrated health using an alternative approach in the evaluation ofrelative deprivation—to be relatively deprived was defined ashaving an income below 70% of the mean income level in thereference group.10 Data from three Nordic countries showedthat the high relative income position in the country ofresidence was strongly associated with lower odds of longstanding illness.11
On the other hand, recent studies in Britain only partially
support the relative deprivation hypothesis. Jones and Wildman
used 11-year panels from British Household Panel Survey andreported mixed results across models using the Yitzhaki index.16
Using the same sample, Lorgelly and Lindley also failed tocorroborate the hypothesis.17 Gravelle and Sutton found very
weak association between relative deprivation and poor selfassessed health among men in British General Household
Survey samples.15 However, the study by Jones and Wildman
indicated a positive result when modelling with ordinary leastsquares (OLS) but not in other approaches (ie, fixed-effect,
random-effect and Houseman–Taylor approaches).16 Therefore,
the discrepancies among studies might be due to the differences
in modelling approaches including covariance adjustment andhierarchical modelling.
Mental disorders (eg, depression) are important consequencesof psychological stress. Eibner and colleagues demonstrated asignificant link between relative deprivation and mental
J Epidemiol Community Health 2009;63:461–467. doi:10.1136/jech.2008.078642

disorder.13 Many studies have reported that depression predicts
functional decline.22 28–32 Increased psychosocial stress due torelative deprivation may make older people vulnerable todepression and subsequent disability. In the present study,
lifestyle factors in part explained the positive association
betweenrelative
deprivationanddisability
onset.
Psychological distress attributed to relative deprivation may
lead to maladaptive health behaviours, thereby leading to early
onset of functional disability.
We found no significant association between relative deprivation and disability among women. As a potential explanation,
household income may not be a good measure capturing therelative socioeconomic position of Japanese female elderly who
are likely to be economically inactive at this stage in the life
course and not the main earner in their households. That is,income might not be an important gauge when people compare
themselves with others. Alternatively, our sample in women
could be more biased given the higher rate of missing data
among females.
The association between relative deprivation and incident
disability was stronger among men with higher incomes,suggesting that the population is more sensitive to psychosocial
stress arising from invidious comparisons. The same pattern
was found in two studies in Nordic countries suggesting thatpsychosocial mechanisms could be more important thanmaterial mechanisms in a relatively egalitarian society (suchas Nordic countries and Japan) where equality is a common
value.10 11 Because wealthier individuals do not suffer material
deprivation in such nations, psychosocial mechanisms may be
the primary pathway linking income inequality and health465

J Epidemiol Community Health: first published as 10.1136/jech.2008.078642 on 12 February 2009. Downloaded from http://jech.bmj.com/ on March 17, 2020 by guest. Protected by copyright.

Research reportWhat is already known on this subject
Although income inequality is hypothesised to be a threat topopulation health, few studies have addressed the mechanisms
through which income inequality adversely affects population
health. Relative deprivation is one such pathway.

What this study adds
Using a large prospective database, this study suggests that
relative deprivation in income is associated with incident
functional disability independent of absolute income amongolder Japanese men but not among women. Lifestyle factors
in part explained men’s excess risk for disability according torelative deprivation.
c Men with higher income may be more vulnerable to relative
deprivation than those with lower income in Japan.
c The potential implication of this study is that disability
prevention should go beyond the individual level and address
broader issues of income distribution in Japanese society.
cFellowship Program administered by the Social Science Research Council and theAmerican Council for Learned Societies in cooperation and with funds provided by theJapan Foundation Center for Global Partnership and in part supported by Pfizer HealthResearch Foundation on the present analysis. SVS is supported by the National
Institutes of Health Career Development Award (NHLBI 1 K25 HL081275). Thesesponsors did not have any involvement in this study’s design, data collection, analysis,
data interpretation and writing. We thank Dr Toshiyuki Ojima, Dr Chiyoe Murata, Dr Kei
Suemori, Dr Yoshitaka Saito and Dr Yukinobu Ichida for their useful comments andsuggestions.
Funding: Ministry of Education, Culture, Sports, Science and Technology of Japan(Grants-in-Aid for Scientific Research: 18390200); The Social Science ResearchCouncil and the American Council for Learned Societies in cooperation and the JapanFoundation Center for Global Partnership (Abe Fellowship Program to NK); Pfizer HealthResearch Foundation; The National Institutes of Health (NHLBI 1 K25 HL081275 to
SVS).
Competing interests: None declared.
Ethics approval: The AGES protocol was approved by the ethics committee in
Research of Human Subjects at Nihon Fukushi University.

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