Association of socioeconomic status with hearing loss in Chinese working-aged adults: A population-based study
Association of socioeconomic status with hearing loss in Chinese working-aged adults: A population-based study
Ping He 0 1 2
Yanan Luo 0 2
Xiangyang Hu 0 2
Rui Gong 0 2
Xu Wen 0 2
Xiaoying Zheng 0 2
0 Funding: This study was supported by the Theoretical and Practical Research Project of China Disabled Persons' Federation (2014-2015) (Grant No. 2014&ZZ028), the Key National Project (973) of Study on the Mechanisms of Interaction between Environment and Genetics of Birth Defects in China (Grant No. 2007CB5119001), the
1 China Center for Health Development Studies, Peking University , Beijing , China , 2 Institute of Population Research, Peking University , Beijing , China , 3 Bloomberg School of Public Health, Johns Hopkins University , Baltimore, MD , United States of America, 4 China Rehabilitation Research Center for Deaf Children , Beijing , China , 5 APEC Health Science Academy (HeSAY), Peking University , Beijing , China
2 Editor: Susan D. Emmett, Duke University School of Medicine and Duke Global Health Institute , UNITED STATES
Hearing loss is the most common sensory impairment, but limited studies focused on the association of socioeconomic status (SES) with hearing loss among adults of working age. This paper aimed to fill this gap among Chinese adults. We obtained data from Ear and Hearing Disorder Survey conducted in four provinces of China in 2014±2015. The survey was based on WHO Ear and Hearing Disorders Survey Protocol and 25,860 adults aged 25 to 59 years were selected in this study. Trained local examiners performed pure tone audiometry to screen people with hearing loss, and those who were screened positively for hearing loss were referred to audiologists to make final diagnosis. SES was measured by occupation, education and income. Results show after adjusting for SES measures and covariates, in urban areas, compared with white-collar workers, blue-collar workers and the unemployed were more likely to have hearing loss, with an odds ratio of 1.2 (95%CI: 1.0, 1.3) and 1.2 (95%CI: 1.0, 1.4), respectively. Compared with people with education of senior high school or above, those with junior high school, primary school and illiteracy had 1.6 (95%CI: 1.4, 1.8), 2.1(95%CI: 1.7, 2.5) and 2.6 (95%CI: 1.9, 3.7) times as likely to have hearing loss, respectively. In rural areas, the unemployed had 1.5 (95%CI: 1.0, 2.3) times the risk of hearing loss compared with white-collar workers, and illiterates had 1.6 (95%CI: 1.6, 2.1) times the risk of hearing loss compared with people with education of senior high school or above, after SES variables and covariates were taken into considerations. Income was not significantly associated with hearing loss in urban and rural areas. In conclusion, SES, in the form of occupation and education, was associated with hearing loss among working-aged population, and further studies are needed to explore the mechanism of such association.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Hearing loss is the most common sensory impairment and has become a public health concern
]. Hearing loss represents a frustrating condition, which is associated with
Key State Funds for Social Science Project
(Research on Disability Prevention Measurement in
China, Grant No. 09&ZD072), and the State
Scholarship Fund (Grant No. 201606010254).
communication difficulties, impaired cognitive functioning, and reduced quality of life [
The recent Global Burden of Disease Study 2013 showed that hearing loss had been ranked as
the fifth leading cause of years lived with disability, higher than other chronic diseases
including diabetes, dementia, and chronic obstructive pulmonary disease[
]. In china, a study
found that 10.41% of people aged 15±59 years were diagnosed with hearing loss in 2015.
Working-aged adults, defined as people aged 25±59 years in China, accounted for roughly
53% of the total population[
]. An increasing number of individuals in this age group had
diabetes, hypertension and noise exposure, and the presence of these conditions were associated
with higher rates of hearing loss[
]. In addition, working-aged people often face multiple
physical and psychological stresses, such as stressful responsibility, job dissatisfaction and
mental stress at work[
], and therefore these stresses interacted with complex feed-back
neuroendocrine systems and immune system could contribute to hearing loss[
Socioeconomic status (SES), is associated with hearing loss[11±14], but studies on this topic
among working-aged population are realtively limited[
]. Studies have shown that lower SES
was associated with higher risk of hearing loss in adults of working age[
education and income were commonly used as SES measures to examine their relationship
with health in China[
]. Up to now, there are no studies on the association between SES
and hearing loss in Chinese working-aged adults. Therefore, more knowledge about this issue
is needed for this population in China.
In this study, using a cross-sectional, population-based Ear and Hearing Disorder Survey in
four provinces of China, we aimed to examine the relationship between SES and hearing loss
in Chinese adults aged 25 to 59 years. This study will fill the gap on this topic for China and
contribute to world literature in the context of eastern countries.
We obtained data from Ear and Hearing Disorder Survey, which was a population-based study
conducted in four provinces of China (Jilin, Guangdong, Gansu, and Shaanxi) between August
2014 and September 2015. The survey design was established by a technical team based on
WHO Ear and Hearing Disorder Survey Protocol , which has been used in China [20±23].
The screening scale of audiometry was on the basis of the modified version of the WHO/PBD
Ear and Hearing Disorders Examination Form (Version 8.3).
The sampling frame covered almost 200 million people, representing about one in seven of
the total population in China. Probability proportion to size (PPS) sampling method was used
to identify 144 sites from 24 counties or districts in four provinces. Each site included 100
households which had lived in the registered address for over 6 months. A total of 47,511
individuals were randomly selected and 45,052 of them participated in the survey, yielding a
participation rate of 94.8% [
]. All participants consented to participate in the survey, and if
required, to be subsequently examined by audiologists.
In this study, we restricted our analysis to 26,000 adults at the ages between 25 and 59 years,
and after excluding 160 missing values, we obtained 25,840 individuals for analysis. Fig 1
presents more details on the sample selection of this study.
Audiometry was performed by trained examiners according to the established protocols of Ear
and Hearing Disorder Survey. Examiners were recruited from local primary health care
institutions (village doctors in rural area and community physicians in urban area), and were
trained by provisional technical teams in survey skills and audiological techniques. Before the
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Fig 1. Flowchart of the study sample.
household survey, examiners went to local sites to select audiometric test rooms with ambient
noise levels not exceeding 40 dBA measured by sound level meters, and were equipped with
MADSEN-Xeta pure tone audiometers and other required examination equipment. During
the survey, noise-excluding headsets would be used if the ambient noise of testing rooms
exceeded 40dB. Audiometric equipment was calibrated by a laboratory at the beginning and
end if a study, and on a daily basis by team members using self-calibration against their known
hearing levels. During and after the survey, a subsample with 5% of participants were
rechecked and the consistence rates of rechecks both reached 90% and above [
Examiners performed pure tone audiometry among people aged 25±59 years in a selected
quiet room. Both ears were tested separately at 0.5, 1, 2, and 4 kHz to obtain the hearing
threshold on each frequency point. There were no people who could not have both ears tested
due to injury or ear infection in our survey. For those who could only have one ear tested, we
performed audiometry in the better ear. Pure tone threshold averages in the better ear were
calculated to identify grades of hearing loss according to the standard of WHO/PDH/97.3
, and the categories were collapsed into two groups: not having hearing loss ( 25dB) and
having hearing loss (> 25dB). Afterwards, those suspected patients with hearing loss were
referred to audiologists for final diagnosis of hearing loss. The referred audiological data were
used in this study.
This survey was ethically approved by China Disabled Persons' Federation (number:
2014&ZZ028). The committee board, which was composed of audiologists and
epidemiologists, reviewed the study protocols and ethical situations. The authors had no access to
identifying information for the study participants prior to data analysis. All participants signed the
informed consent with interviewers to participate in the survey and clinical diagnosis. For those
with severe hearing loss who were unable to sign the consent, family members represented
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them to sign the consent. We obtained data from this survey, which was performed
independently from this specific study.
The outcome variable was whether or not an adult had hearing loss. The independent variable
was socioeconomic status, defined by three categorical variables: occupation (white-collar
worker, farming worker, blue-collar worker, others and the unemployed), education (illiteracy,
primary school, junior high school and senior high school or above) and income (quintiles of
annual family income per capita). White-collar workers in this study involved professional
and governmental employees, and blue-collar workers referred to manual and
services-oriented workers excluding farmers. Covariates included gender (male and female), having
spouse (yes and no) and age group (25±29, 30±39, 40±49 and 50±59 years). The independent
variables and covariates were all self-reported.
Logistic regression models were used to evaluate multivariate associations between hearing
loss and SES variables, and the odds ratios (ORs) with 95% confidence intervals (CIs) were
presented. Although socioeconomic indicators are correlated, occupation, education and income
are not interchangeable [
]. Therefore, we need to control for each socioeconomic indicator
and related covariates to obtain the ªnet effectº of each SES measure. A P value less than 0.05
was considered statistically significant. The software Stata version 13.0 for Windows (Stata
Corp, College Station, TX, USA) was utilized for the statistical analysis. All analyses were
conducted separately by urban and rural areas.
Table 1 shows the characteristics of participants by urban and rural samples. In urban areas,
among individuals with hearing loss, 39.2% of them were blue-collar workers, 50.9%
completed education of senior high school or above, 34.7% were from the highest-income families,
52.4% aged 50±59 years, 56.5% were male, and 89.6% had a spouse. In rural areas, among
individuals with hearing loss, 78.0% of them were farmers, 43.7% completed education of junior
high school, 33.9% were from the lowest-income families, 53.9% aged 50±59 years, 55.0% were
male, and 93.2% had a spouse.
Table 2 presents the prevalence of hearing loss in adults aged 25±59 years in urban and
rural areas. In both urban and rural areas, white-collar workers had the lowest prevalence of
hearing loss. The prevalence of hearing loss increased with decreasing level of education in
both urban and rural areas. Hearing loss seemed not to be associated with income in urban
areas, but to be associated with lower level of family income in rural areas. In both urban and
rural areas, the prevalence of hearing loss increased with increasing age. Males and people
having a spouse had higher prevalence of hearing loss in both urban and rural areas.
Table 3 shows logistic regressions on the association between SES and hearing loss among
adults aged 25±59 years in urban areas. In Model 1 containing all SES measures, income was
not significantly associated with hearing loss, but occupation and education were significantly
associated with hearing loss. After further adjusting for gender, having spouse and age group
in Model 2 and Model 3, the association of occupation and education with hearing loss
remained significant despite its magnitude became smaller. In Model 3, compared with
whitecollar workers, blue-collar workers and the unemployed were more likely to have hearing loss,
with an odds ratio of 1.2 (95%CI: 1.0, 1.3) and 1.2 (95%CI: 1.0, 1.4), respectively. Compared
with people with education of senior high school or above, those with junior high school,
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primary school and illiteracy had 1.6 (95%CI: 1.4, 1.8), 2.1(95%CI: 1.7, 2.5) and 2.6 (95%CI:
1.9, 3.7) times as likely to have hearing loss, respectively.
Table 4 presents logistic regressions on the association between SES and hearing loss
among adults aged 25±59 years in rural areas. In Model 1 and Model 2, occupation, education
and income were each significantly associated with hearing loss. In Model 3 which further
adjusted for age group, the association of income with hearing loss became not significant, and
the association of occupation and education with hearing loss remained significant and its
magnitude turned out to be weaker. The unemployed had 1.5 (95%CI: 1.0, 2.3) times the risk
of hearing loss compared with white-collar workers. Illiterates had 1.6 (95%CI: 1.6, 2.1) times
the risk of hearing loss compared with people with education of senior high school or above.
In this study, SES, as defined by occupation, education and income, was investigated regarding
its association with hearing loss in working-aged adults in a population-based Earing and
5 / 12
Hearing Disorder Survey in four provinces of China. According to the WHO Ear and Hearing
Disorders Survey Protocol, individuals were first screened by local trained examiners using
pure tone audiometry and were further referred to audiologists for final diagnosis of hearing
loss. To the best of our knowledge, this is the first to investigate the association between SES
and hearing loss in adults of working age from a population-based survey in China. We found
that lower SES, in the form of occupation and education, was associated with higher risk of
hearing loss in both urban and rural areas.
Our findings showed that lower-class occupation was correlated with higher level of hearing
loss, which is consistent with previous research[
]. In this study, compared with white-collar
workers, blue-collar workers and the unemployed were more likely to have hearing loss in
urban areas, and the unemployed were more prone to having hearing loss in rural areas. The
correlates of occupation with hearing loss were likely because of the connection with
jobrelated exposure and social standing [
]. For instance, blue-collar workers, including manual
and services workers, were more inclined to exposure to risk factors of hearing loss [
as ototoxic chemicals[
], working environment noise and whole-body vibration [
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addition, the association of the unemployed with greater risk of hearing loss is partly due to
their poor hearing knowledge as well as less access to care for hearing conditions[
This study indicated that lower education was associated with elevated level of hearing loss
when a wide range of covariates were taken into consideration, which is consistent with prior
]. Although little is known about the causal mechanism between education and
hearing loss, we can speculate some potential reasons. For example, lower education is a
marker of unhealthy lifestyle attributes, including higher prevalence of alcohol intake, smoking
and obesity [
], which are related to greater risk of hearing loss [
]. In addition, adults
with higher level of education may have better birth hearing status [
], better access to health
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care for hearing-related conditions, and less workplace stress [
]. Furthermore, individuals
with hearing loss have been shown to perform worse in school and are more likely to drop out
Our study found that income was not associated with hearing loss among working-aged
adults in urban and rural areas. Lower income is usually linked with poor access to, utilization
of, and quality of health care and then correlated with poorer health status [
mechanism may adapt to hearing conditions, leading to greater risk of hearing loss in lower-income
adults. However, we did not observe the inverse association of income with hearing loss after
adjusting for SES measures and covariates in urban and rural areas. This is not consistent with
previous studies on the association between income and hearing impairment among
working8 / 12
aged adults aged 25±64 years in the United States [
], or not consistent with studies in adults
aged 18±64 years in the Netherlands [
] and adults aged 20±74 years in Canada [
This study has several limitations. Since some factors that may affect response variability
were not considered, we need to take caution to interpret our results. For instance, the main
purpose of this study was to investigate the association between SES and hearing loss, but
some risk factors, such as noise exposure, chronic diseases (i.e. hypertension and diabetes) and
cigarette smoking, may contribute to the observed association [
]. In addition, although SES
was commonly measured by occupation, education and income, research has found that
failure to include wealth indicator could underestimate the effect of health [
one person's SES may be correlated with the SES of their parents and spouse. However, due to
restriction of our study design, we did not include these covariates in this study. Finally, a
cross-section design for this study cannot draw causal inferences. Hearing loss in early life
may also result in lower levels of education, income and employment opportunities in
adulthood . From this perspective, further studies are necessary to investigate the causality and
its pathways between SES and hearing loss drawing from prospective cohort design.
Despite these limitations, the strengths of this study include a large-size, population-based
design in four provinces of China based on the WHO Ear and Hearing Disorder Survey
Protocol, access to a variety of socioeconomic measures and multiple covariates in the association of
SES with hearing loss, as well as hearing conditions ascertained by audiologists according to
the WHO criteria.
This study investigated the association between SES and hearing loss among working-aged
adults aged 25 to 59 years in four provinces of China. We found that SES, in the form of
occupation and education, was associated with hearing loss. However, income was shown not to be
associated with hearing loss in our findings. This study contributes to the literature on hearing
loss in developing nations of a non-Western context. Further studies are warranted to confirm
our findings and to better understand how SES is related to hearing loss, which will help
identify how to prevent hearing loss and to provide more specific suggestions to improve hearing
status for working-aged population.
This study was supported by the Theoretical and Practical Research Project of China Disabled
Persons' Federation (2014±2015) (Grant No.2014&ZZ028), the Key National Project (973) of
Study on the Mechanisms of Interaction between Environment and Genetics of Birth Defects
in China (Grant No. 2007CB5119001), the Key State funds for social science project (Research
on Disability Prevention Measurement in China, Grant No. 09&ZD072), and the State
Scholarship Fund (Grant No. 201606010254).
Conceptualization: Ping He, Xiaoying Zheng.
Data curation: Yanan Luo, Rui Gong, Xu Wen.
Formal analysis: Ping He, Yanan Luo.
Funding acquisition: Ping He, Xiangyang Hu, Xiaoying Zheng.
Investigation: Xiangyang Hu, Rui Gong.
Project administration: Xiangyang Hu.
9 / 12
Supervision: Xiaoying Zheng.
Writing ± original draft: Ping He, Yanan Luo.
Writing ± review & editing: Xu Wen, Xiaoying Zheng.
10 / 12
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