Health-related quality of life in Chinese workers: a systematic review and meta-analysis

Background Studies of health-related quality of life among workers have generated varying results. The purpose of this study was to conduct a systematic review to synthesize the scores of health-related quality of life measured by the World Health Organization Quality of Life questionnaire among Chinese workers and compare the results across gender, age, occupation and region. Methods Six databases including China National Knowledge Infrastructure, WanFang Data, China Science and Technology Journal Database, PubMed, Web of science and Scopus were searched for relevant publications in both English and Chinese from their inception to February 2021. Inclusion and exclusion criteria were established, and study and participant characters as well as health-related quality of life scores were extracted from included publications. Study quality was assessed by using the Crombie tool. The meta-analysis including individual publications used random-effects models. Subgroups analyses by gender, age, occupation and region were also conducted to explore the source of heterogeneity. Results One hundred thirty-nine out of 1437 potential publications were included. The pooled mean scores of health-related quality of life were 14.1 for the physical domain (95%CI: 13.9–14.3), 13.7 for the psychological domain (95%CI: 13.5–13.8), 14.0 for the social relationship domain (95%CI: 13.8–14.2), 12.3 for the environment domain (95%CI: 12.1–12.5). No significant statistical difference was found between the different subgroups. Publication bias was present in the independence domain and the pooled scores were corrected to 15.0 (95%CI: 14.6–15.5) using the trim and fill method. Sensitivity analysis suggested that the results of the meta-analysis were stable. Region might be a source of heterogeneity. Workers in northeast China reported higher scores in the social relationship domain, and those in the central region reported lower scores in the environmental domain. Conclusions Chinese workers reported lower scores in four health-related quality of life domains than the general population. Region might be a potential influencing factor for workers’ scores different, which needs further study. The pooled scores can served as benchmarks for workplace health promotion programes in Chinese workers and global occupational health studies.


Background
Health-related quality of life (HRQOL) is defined by the World Health Organization (WHO) as "individuals' perceptions of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns" [1]. According to this definition, HRQOL is not only related to an individual's health status but also to their personal satisfaction. Therefore, HRQOL can vary greatly between China and other regions with different languages and culture. HRQOL instruments have been widely used in China since the 1980s. The Chinese versions of the World Health Organization Quality of Life (WHOQOL) questionnaire including WHOQOL-100 and WHOQOL-BREF were translated by Fang and his colleagues and were shown to have good reliability and validity in the Chinese population [2]. WHOQOL-BREF (26 items) is a simplified version based on WHOQOL-100 (100 items). The items from the two scales were grouped into 4 domains: physical health, psychological health, social relationship and environment as well as evaluate general HRQOL and general health. The scores in each domain have good comparability between the two scales: the Pearson correlation coefficient ranges from 0.89 (the social relationship domain) to 0.95 (the physiological domain) [3]. WHOQOL-100 includes two additional domains: independence and spirituality beliefs.
Occupational activities run through most people's lives, and working conditions and environments have been recognized as important health determinants, i.e. key drivers of HRQOL. Different occupational groups may experience various and different health problems due to the nature of their jobs, with different performance in HRQOL. For example, high physical work demand and awkward static/repetitive working postures may contribute to higher incidence of musculoskeletal disorders [4,5]; shift work is related to cardiovascular heart disease and mental disorders [6,7]; and sedentary behavior is a risk factor for chronic diseases including obesity, diabetes, etc. In addition, male and female workers at different ages may have different types of job, e.g. nurses and teachers are mostly women, while bluecollar workers (such as construction workers and miners) are mostly young men. Therefore, it is important to assess HRQOL by gender, age and occupation to identify differences and group time trends with a view to providing group specific occupational health services. The influence of different geographical regions on the results also needs to be explored, taking into account differences in climate, lifestyle and subtle cultural differences.
Although individual studies have reported results based on WHOQOL in Chinese workers engaged in different occupations, there has been no other systematic review summarizing these findings. Therefore, the primary objective of this systematic review was to summarize the findings around six HRQOL domains in Chinese workers, so as to provide references for future studies and for health policy (Studies using either of the two versions of the questionnaires generated the scores for physical health, psychological health, social relationship and environment domain, while only those using WHOQOL-100 generated the scores for independence and spirituality beliefs domain). The second objective was to compare the results across gender, age groups and occupational groups in order to explore the characteristics of different subgroups and identify more vulnerable groups.

Methods
The protocol for this systematic review with metaanalysis was registered in the International Prospective Register of Systematic Reviews (PROSPERO, Registration ID: CRD42020151775). The current review was reported by following the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) Statement [8]. Two reviewers (SU and LIU) independently searched and selected the publications. Any disagreement led to a consultation with the third reviewer (JIN) and resolved by reaching consensus.

Data sources and search strategy
Potential publications were identified from six databases searched from their inception and up to February 2021: China National Knowledge Infrastructure (CNKI), Wan-Fang Data (WF), China Science and Technology Journal Database (CQVIP), PubMed, Web of Science and Scopus. Of these databases, CNKI, WF and CQVIP mainly covered Chinese publications. Keywords, medical subject heading (MeSH) terms and free-text words were used as searching strings. The search strategy incorporated two principal components. The first related to the study population: Chinese workers with active employment and engaged in any specific industries. The second related to the health outcome, namely HRQOL evaluated by WHOQOL-BREF or WHOQOL-100. The exact search strategies are presented in Table 1.

Study eligibility
The inclusion criteria were as follows: (1) cross-sectional study, or cohort, intervention study reporting baseline data; (2) conducted in the Chinese mainland; (3) active occupational population with specific occupation; (4) HRQOL measured using WHOQOL-BREF or WHOQOL-100; (5) publications in Chinese or English until February, 2021. Publications were excluded if they: (1) did not report specific scores or standard deviations; (2) reported nonstandard data (incomparability data that were not calculated according to standard methods); (3) included workers with specific diseases; (4) repeated findings from other analyses that measured the same population at the same study period; (5) were special groups providing goods or services prohibited by local law (e.g. sex workers).

Data extraction
The extracted data from the included publications contained: (1) study characteristics (author, published year, etc.); (2) participant characteristics (age, gender, occupation, region, response rates etc.); (3) health outcomes (sample sizes, average scores and standard deviation for different domain of HRQOL). Microsoft Excel 2016 was used for data management.

Quality assessment
The methodological quality of each study was evaluated using a well-established quality appraisal tool recommended by Crombie [9]. The tool and its modified version have been used in many systematic reviews [10][11][12]. The tool consists of 7 items with responses "Yes (1 point)" or "No (0 point)". Consequently, each study provided a score between 0 and 7. The scores were grouped into: ≤5 (low quality) and > 5 (high quality).

Statistical analysis
To ensure comparability of data, scores on a 0-100 scale were transformed to a 0-20 scale following a procedure stated by the WHOQOL User Manual [13]. A meta-analysis was conducted for each domain of HRQOL to estimate the combined means and 95% confidence intervals. The test for heterogeneity among results and the selection of random effects model or fixed effects model were determined according to the I-squared statistics. Publication bias was assessed by Funnel plot, Egger's test and Begg's test. A p-value < 0.05 was considered statistically significant publication bias. The trim and fill method was further used to assess the influence of bias on the results. Influence analysis was conducted with each study deleted from the model to explore the stability of the results in the meta-analysis. Stata 15 was used for statistical analysis. Figure 1 shows the flow diagram describing the study and publication selection process. A total of 1437 publications were initially identified from the databases or the related references, 1026 remained after removing duplicates electronically or manually. Next, 795 and 92 publications were removed by screening titles/abstracts and full text according to inclusion and exclusion criteria. Of the excluded full-text publications, 34 publications were found reported duplicated findings, and 11 publications were found reporting nonstandard data. The remaining 139 remained for quantitative synthesis.

WF
-主题:("员工" OR "人员" OR "职员" OR "工人" OR "农民工" OR "务工" OR "工作 者" OR "公司" OR "职业") 摘要:("世界卫生组织生存质量" OR "WHOQOL") The study quality assessment of those publications can also be seen in Table 2. The average score was 4.7, ranging from 3 to 7. 74.8% (n = 104) of publications were rated as having low study quality. The variation in scores mainly reflected in the items "appropriateness of design to meet the aims" and "clearly stated aims and likelihood of reliable and valid measurements". Only 9 publications explicitly stated that random sampling or the whole population was used, and only 54.7% (n = 76) reported reliability or validity of the questionnaires used in the investigation.

Meta-analysis
The scores in the physical (n = 138), psychological The analysis included publications from 2001 to 2021. HRQOL scores in the six domains each year were similar and showed no trend over time (P > 0.05). The maximum differences in the mean score for the physical, psychological, social relationship, and environment domain from year to year were 1.8, 1.4, 1.1, and 2.3, respectively.

Publication bias assessment and sensitivity analysis
Visual inspection of the funnel plot (Fig. 3), Egger's test and Begg's test did not suggest publication bias in the meta-analysis of the physical, psychological, social relationship environment and spirituality beliefs domains (P > 0.05). However, Egger's test suggested potential publication bias in the independence domain (P = 0.011), while Begg's test did not (P = 0.853). Therefore, the trim and fill method was also applied, and it indicated that if 4 estimated missing publications were added, then the pooled score of the independence domain would change

Subgroup analysis
The data in the included publications were further analyzed by gender, age, occupation and region. Publications presenting multiple subgroups were included in the subgroup meta-analysis if the scores were reported for the respective subgroups. The gender characters were categorized into three based on gender dominance: male-dominated (> 80%, n = 49), female-dominated (> 80%, n = 60), and mixed (n = 34). 17 publications did not report participants' gender and 22 publications reported age-specific results. The mean age of participants was divided into 3 categories: 19.8-29.9 (n = 38), 30.0-39.9 (n = 72), and 40.0-66.5 (n = 8). Twenty publications did not report the mean age or sample size of each age group. The occupations were grouped into three: workers in mining, construction and manufacturing were classified as blue-collar workers (n = 51); education, logistics and company staff as office workers (n = 20); and doctors, nurses and medical rescue workers as health care workers (n = 70). In addition, 2 publications reported occupation-specific results. Besides, we divided China into 8 geographical regions: central (n = 16), north (n = 26), east (n = 33), south (n = 25), southwest (n = 13), northeast (n = 6), northwest (n = 7). Twelve publications did not report the study region.
The pooled mean scores and 95% confidence intervals for the four HRQOL domains for each subgroup are presented in Table 3. No significant differences were found among different gender, age, and occupation groups, so these factors could not be regarded as sources of heterogeneity. The differences among regions were mainly reflected in social relationships and environmental domain. The pooled score of social relationship domain in northeast China was higher than that of other regions, while the pooled score of environmental domain in Central china was lower than that of other regions.

Discussion
Meta-analysis is increasingly being utilized in the health field. Meta-analysis of studies without control groups, with continuous outcome variables, only provide data for specific populations. Although investigations of HRQOL in different occupational groups have been conducted in several regions of China, there is great variation by gender, age, occupation and sample size, and these discrete results may therefore be difficult to compare between studies or use as an index to reflect changes after implantation of policy or health program. Therefore, we systematically reviewed the literature on occupational quality of life and attempted to estimate combined scores. A total of 139 publications were included in metaanalysis, of which 136 were based on cross sectional studies, and 3 on intervention studies. Similar to most studies [153], the results of our meta-analysis on Chinese occupational groups showed that higher scores were found in the physical and social relationship domain than in the psychological domain, followed by the environment domain. Compared to the results from two large surveys conducted in China, a survey of 777 healthy participants [2] and a survey of 83,666 adults [154], our pooled scores were lower in all four HRQOL domains. This may be due to the difference between our study and the two surveys in sampling strategies. The two surveys targeted general adults which may have some systematic difference in occupation distribution. However, this difference could not be verified because these two surveys did not report data on occupation composition. The publications we included were presenting vulnerable occupational groups with impaired well-being, such as workers with heavy physical load, high work intensity and high psychological pressure.
Although subgroup analyses were conducted to explore the source of heterogeneity, no statistical differences were found among gender, age, and occupation groups. Different results across regions might be due to the differences in population distribution and resource allocation. Central China, including Hubei, Hunan, and Henan province, is a densely populated area, thus per capita resources in transportation, living conditions and medical services are relatively less. However, the influence of differences in occupation distribution cannot be excluded. All the above three occupational groups have their own specific occupational risk factors associated with poor HRQOL. Previous studies have shown that bluecollar workers often have harsh working conditions including ergonomic, environmental and psychological hazards. For example, heavy physical load, awkward working postures, vibration, extreme temperatures, noise, harmful chemicals were correlated with musculoskeletal disorders, heat-related illness, skin and lung diseases, and can lead to poor physical health [155][156][157][158]. A higher incidence of non-fatal work injuries and fatalities has also been seen among blue-collar workers, especially construction workers. From 2014 to 2018, 3024 municipal work accidents were reported in China, resulting in an average of 717 deaths per year in China's construction industry [159]. Moreover, supervisor and coworkers support in the work environment were found to be essential predictors of the psychological health, social relationship and environmental domains of HRQOL [160].
For office workers, lack of ergonomic-featured office equipment, sitting, standing and watching computer screens for a long period, and lack of exercise, were related to arm, neck, shoulder and lower limbs pains as well as eye problems [161][162][163]. In addition, due to the low requirements for physical burden, office workers' on-boarding health screening may be not as strict as blue-collar workers, and were less likely to quit work because of acute injuries. For health care workers, increased number of hospital visits by an aging population, strained doctor-patient relationships, and poor sleep habits are important detrimental factors for physical and psychological health, which can lead to occupational stress, depression, burnout and physical exhaustion [144].
Sex work is illegal and not considered as an occupation in China, therefore related publications were not included in our study. Jiang et al. found that female sex workers reported lower scores than women in general in the social relationship and environment domain, which was ascribed to high population mobility and lack of occupational safety and health services. Wang et al. [164] reported lower scores for sex workers than for the general population in the physical domain, which might be related to multiple sexual partners.
As a health indicator, the assessment of quality of life makes it possible to prospectively study of diseases. Our study summarizes overall HRQOL levels among Chinese occupational groups and provided a potential reference for future study. Based on our study, it appears that there remains a need to strengthen the occupational safety and health management of vulnerable occupational groups and reduce exposure to known health risk factors in the future. Government departments also need to rationally allocate resources such as medical care, housing conditions and transportation according to regional factors like economic development level, industrial distribution and employment status, etc. However, close observing the trend of HRQOL over time and identifying essential contributors in the next step are imperative for relevant policy planning.
The results of our study may be biased. The study quality of the included publications was often not satisfactory because of improper sampling methods and unverified reliability and validity. Besides, about half of the included publications focused on medical staff, thus the pooled scores might be close to their results. There are also some publications that reported the results of subgroups (such as migrant workers and urban workers) rather than the entire study population, and the combination of data may induce bias. In Chinese culture, endurance was considered as a merit and people tend to underreport their discomfort. In addition, people also prefer to choose medium instead of extreme figures, which may result in similar results.
There are several limitations to the study. First, the absence of blinding (author and publication information disclosed) used in the search and selection of publications may have leaded to researcher bias. Second, although the search strategy was comprehensive, there may still have been additional studies not indexed by the selected database. Third, given the difficulties in comparing results based on different HRQOL instruments, our systematic review excluded studies that used other instruments (such as 36-Item Short-Form Health Survey, the symptom checklist-90) than WHOQOL-100 or WHOQOL-BREF. Fourth, of the included publications, some did not report the average age, gender and occupation of the participants, which may represent a group of workers with distinct results and lead to bias for subgroup analysis.

Conclusion
This is the first systematic review to synthesize the HRQOL scores for Chinese workers. The pooled scores in HRQOL were lower than those in the general population. Subgroup analysis did not suggest a strong relationship of gender, age and types of job with HRQOL scores, and region might be a source of heterogeneity. We suggest that future HRQOL studies pay more attention to these factors so that effective occupational safety and health targeted to specific groups can be developed and implemented.