Determinants of managers' self-rated health in Chinese petroleum-producing enterprises

Background Self-rated health (SRH) is widely used by health institutions due to its validity, reliability, predicted power for mortality and morbidity and simplicity of collection. However, limited research has been conducted to measure the health and explore the determinants of SRH among managers, especially in petroleum enterprises in China. The purpose of this study was to measure the overall health and identify the determinants of SRH among managers in petroleum production enterprises in China. We committed to provide evidence to improve managers’ health status by exploring the determinants of SRH. Methods From March 2017 to December 2018, 417 managers participated and were categorized into different gender and age groups. The effective rate was 84.2%. The scores for physical, mental and social health subscales were converted to binary categorical variables, and univariate and multivariate logistic regression analyses were used to identify the determinants of SRH. Results The mean scores for SRH measurement scale (MS) dimensions ranged from 65.69 ± 18.13 (mean ± SD) for positive emotion (M2) to 91.81 ± 15.18 for daily physical activities (B2). The findings showed that lower-income and medium-managerial-level managers in the 41- to 50-year-old age group and lower-income male participants were more likely to be of poor mental health, while lower-income managers in the middle age groups and middle-aged female managers tended to report poor social health. Conclusions This study is the first in the Chinese energy industry to report on SRH and its determinants among managers stratified by age and gender. We found that income and managerial level are the main determinants among the managers,

especially for those of middle age. Psychological counseling and a harmonious and mutually supportive working environment can contribute to addressing the special needs of managers in Chinese petroleum-producing enterprises.

Background
Over the past several decades, the overall health of the Chinese population has steadily improved; therefore, today, the focus of primary medical care has shifted from infectious diseases to chronic diseases [1,2] . Self-rated health (SRH) is considered a valuable source of information on subjective health status [3] , especially in tracking chronic diseases, and it forms an essential supplement to objective health measurements. In addition, researchers have found that SRH is a strong predictor of subsequent mortality [3,4] ,with a high reliability, validity and predictive power for a variety of illnesses and conditions [5] . In addition, SRH has economic benefits and is suitable for the measurement of the health status of the population on a large scale [5] . To date, SRH has been used for population health monitoring by WHO, the Centers for Disease Control and Prevention in the United States and the European Union Commission [6][7][8].
The determinants of SRH have been researched adequately in Western countries.
The literature reports that socio-economic situations and demographic factors can affect health outcomes. For instance, Gilmore et al [9] and Asfar et al [10] found differences in SRH between men and women. Roberts [11] and Damian et al [12] reported the relationship between SRH and age. Cai et al [13] , Lorraine et al [14] and Tajvar et al [15] reported the relationship between SRH and income. Further, Demirchyan and Thompson [16] and Lorraine et al [14] demonstrated that education level is a determinant of SRH. The study by Damian et al [12] indicated that the influence of social class on health is significantly modified by age. Researchers have found that the determinants of health differ between males and females.
Having healthy managers is crucial for organizations to remain productive and competitive, because the health of managers is meaningful not only for the managers themselves, but also for the organization and for its staff [17] . However, managers have long been recognized as being among the most stressed members of the workforce [18] . According to research by Nyberg and co-workers, even though managers tend to report high satisfaction with their work and life compared with non-managers [19] , previous studies have indicated that many managers perceived their work as stressful, mainly resulting from their responsibility for reaching corporate objectives [20,21] . Some managers suffer continuously from a shortage of social support, personal life-work interference and high workload. Research has found that employees in the petroleum and gas industries are exposed to numerous physical and psychosocial stressors such as cramped physical environments, long work shifts, isolated location, noise, operating hazards and a lack of social support [22,23] .
Some studies have found that for different groups of people, the determinants of health may be different, due to the differences in cultural backgrounds and labor organization among countries and the specifications of the energy industry. Health status and determinants among managers in the petroleum industries in China need to be researched. Limited studies have been conducted about SRH and its determinants in managers in China, especially in the petroleum production industries.
In this study, we aimed to assess the SRH of managers in petroleum enterprises in China, to identify the determinants among them, to find the vulnerable groups and focus on improving their health status.

Research population
This was a cross-sectional study of a cluster sampling of managers selected from among the general managers in petroleum-producing enterprises in China. There are 31 provinces in mainland China, which can be divided into four parts -the north-east region, the western region, the middle region and the eastern regionaccording to the level of economic development and administrative divisions. We selected Guangdong, Tianjin to represent the eastern region and Heilongjiang to represent the north-east region. Sichuan, Yunnan, Inner Mongolia represented the western region in this study. The sampling method was based on a stratified purpose sampling approach, and therefore the survey of the managers in these provinces can well represent all petroleum managers in China. In each selected province, we used cluster sampling and enrolled all of the managers who took part in health management lectures specifically for petroleum enterprise managers.
From March 2017 to December 2018, the participants were gathered in a meeting room after the lecture and completed the questionnaires in 10 to 15 minutes. The integrity of the returned questionnaires was checked by our investigators in the field. Questionnaires with more than 30% missing data were excluded from the analysis.

Questionnaire
The questionnaire included SRH measurement scale (SRHMS) and general information questions. Unlike the single-item measures of SRH, such as "How do you rate your health today?", SRHMS includes physical, mental and social subscales to measure the overall health status of the general population. SRHMS is consistent with the definition of health by the WHO: Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity [24] .
Previous research has demonstrated that SRHMS is reliable, valid and sensitive and suitable for use in the Chinese population, so we selected SRHMS as a tool to measure self-rated health status in this research.

D e m o g r a p h i c c h a r a c t e r i s t i c s
Previous empirical researches [5,25] reported that demographic factors such as gender, age, marital status and region affected health outcome. In this study, the demographic characteristics included age, gender and regions.
Age was divided into three groups: 30-40, 41-50 and 51-60 years. Region study was divided into east, north-east and west for a total of three groups.

S o c i o -e c o n o m i c s t a t u s
The relationship between socio-economic statusSESand SRH has been documented in many studies. The main indicators of SES were education, employment and income [12,26] . Individuals with lower SES are more likely to have poorer SRH than those with high SES [12,15,25] . Objective measures were used to evaluate SES in this study. In this research, education was divided into three classes: junior college degree, Bachelor's degree and Master's and Doctoral degrees. We used managerial level as the indicator of employment, categorized into Primary, Medium and High.
Income was captured as monthly income and was categorized into three classes [less than 10,000 (RMB), 10,001-15,000 (RMB) and more than 15,001 (RMB)] ( Table   1). F i e l d w o r k All participants completed the questionnaire in the meeting room after lectures.
During this time, the interviewer provided only necessary explanations of unclear questions.

D a t a
The raw score of each of the nine SRHMS dimensions was derived by summing the item scores and converting to a value for the dimension from 0 (worst possible health status measured by the questionnaire) to 100 (best possible health status).
The raw score was then recalculated across the dimension as follows: [Due to technical limitations, the formula could not be displayed here. Please see the supplementary files to access the formula.] Statistical analysis was carried out with SPSS 25.0 for Windows. The statistical description of the demographic characteristics was performed by the use of frequencies, percentages, means and standard deviations.
We analyzed data by using both descriptive and analytical approaches. First, we examined the normality of the data (the scores of three subscales) and found that the score distributions were slightly negatively skewed. So, second, we converted each score of the three subscales to a binary variable. Third, we used univariate The data were analyzed by logistic regression separately for males and females and for different age groups, whereby each exploratory variable was entered separately into the univariate logistic regression. Poor SRH was used as the reference category. Results were presented as odds ratios (OR), and 95% confidence intervals (95% CI) were calculated separately for poor and normal SRH. The descriptive statistics for the study variables are displayed in  In general, managers in Chinese petroleum production enterprises have a relatively higher SRHMS score for daily physical activities (B2 = 91.81) and physical mobility (B3 = 87.53) than for the other dimensions. The scores for the 9 dimensions and three subscales are higher than the scores for the population in similar occupations in 6 provinces in China except for the scores for the social support dimension [27]. D e t e r m i n a n t s o f S R H  (Table 4). However, in other age groups, a similar situation has not been found.  Results of multivariate logistic regression stratified by different age groups are shown in Table 6 and indicate that, among the 41-to 50-year-old age group, managers earning less than 10,000 (RMB) were more likely to be in poor mental health, while lower-level managers were significantly less likely to be in poor mental health.
When taking gender, education level and monthly income into consideration, we found that among managers in the 41-to 50-year-old age group, compared with the managers earning more than 15,000 (RMB), those who earned less than 10,000 (RMB) were more likely to exhibit poor social well-being.

Discussion
In general, based on the findings of this study, we found that monthly income and managerial level are the main determinants of SRH in managers in petroleum enterprises in China, and the result was modified by age and gender.

Age disparity
In the univariate logistic regression analysis, we found that monthly income and managerial level played an important role in mental health among the middle age group, while we find no association among demographic characteristic, SES and SRH among the other two age groups.
When we put monthly income, managerial level, gender and education degree into the multi-univariate logistic regression, we found that, in the middle age group, lower-level managers were more likely to be in good mental health, while lowerincome managers tended to report poor mental and social well-being. Managers in middle age (ages 41 to 50 years in this study) carry an enormous burden from both occupation and life. In this stage of life, most of the managers (95.4%) were above the medium managerial level and had to bear life burdens such as their children's university fees and their parents' health expenditures, which create a daunting occupational and family responsibility. Therefore, they are more likely to react to the influencing factors.
Income is a component of socio-economic status and is considered so important for health that it was even regarded as one of the determinants of health. Empirical research also revealed the relationship between health and income. For example, Cai et al [13] , Lorraine PJ et al [14] and Tajvar et al [15] found that people with higher income reported better health, because sufficient income enables individuals not only to meet the needs of daily life but also to participate in society, enjoy hobbies, holidays and luxuries. Molarius et al [28] reported that lower income increases the risk of mental disorders. There are several theories addressing the mechanisms about how individual income influences people's health. The 'absolute income effect' states that people with higher individual income are able to devote more resources to healthy goods and services that can improve their health directly, while the 'relative income effect' states that the health of those in the lower-income hierarchy is affected because their lower social position increases the likelihood that they will experience stress and frustration, leading to worse health. In the 41-to 50-year-old age group, compared with higher-level managers, the medium-level managers were more likely to be in poor mental health. This difference could be attributed to the fact that higher-level managers usually have more influence, control and freedom to act, as well as better social support, than do lower-level managers. The main role of medium-level managers in traditional Chinese petroleum enterprises is to organize and perform, which means that they have primary responsibility for a specific job. However, they have fewer resources and power to finish the job than do higher-level managers. This can also explain why lower-level managers in the 41-to 50-year-old age group were less likely to report poor mental health when gender and all of the SES indicators were combined in the multi-univariate logistic regression analysis. The job descriptions for lowerlevel managers are less complicated, and they have less responsibility in the job, which results in better mental health.

Gender disparity
Previous studies conducted in the general population had indicated that women were more likely to report poor health [5,15] due to their disadvantages in acquiring resources and occupational opportunities. The studies conducted among managers also found that female managers tended to report poorer health than male managers [18,29] . Female managers reported more psychosomatic concerns, higher emotional demands, low control and low support in their work [18,30] . Conversely, gender disparity in SRH did not exist in this research: Female managers did not report poorer SRH than males in all three subscales. We believe that the weak tie between gender and SRH was related to the relatively fair salary and medical insurance system in Chinese petroleum enterprises. Compared with male managers, female managers did not show obvious disadvantages in accessing resources such as social resources and occupational opportunities.
In the univariate logistic regression analysis stratified by gender, we found that, among the female managers, being in the 41-to 50-year-old age group increased the risk of reporting poor social health compared with the 51-to 60-year-old age group. As we stated before, managers in the 41-to 50-year-old age group are more likely to react to influencing factors. In the dominant Chinese traditional cultural background, females bear more responsibility to care for the family than do males.
In this stage of life, to take care of the family as well as improve income, they devote more time and resources to the family but not to holidays and community and social activities.
Among the male managers, compared with the higher-income group, managers earning less than 10,000 RMB per month were more likely to be in poor mental health. In traditional Chinese culture, household income is provided mainly by men.
On the one hand, income denotes men's dominant positions in a family, but on the other hand, it also means that men are more likely to be influenced by income than are women. Thus, the income disparities are more likely to be observed in males but not in females. According to the 'relative income effect', lower income puts male managers into a lower social position, which increases stress and frustrated emotion.
We found no significant differences in physical health among different gender and age subgroups. The reasons may be related to the sufficient medical knowledge of the participants as well as to the health management program that was introduced to the petroleum enterprises in China in 2007. This program, including an employee assistance program (EAP) and health, safety and environment management systems (HSE MS) reduces the risks inherent in manufacturing procedures and improves the physical health status of the employees [31,32] .
The study is the first in the Chinese energy industry to report on SRH and its determinants among managers stratified by age and gender. However, several limitations in this research need to be taken into consideration: First, the research design was cross-sectional; hence, it was difficult to establish cause-effect relationships among SRH, socio-demographic characteristics and socio-economic status [33] . A prospective study design should be implemented to investigate these relationships in the future. Second, all the information was self-reported data [34] , so recall bias cannot be excluded.

Conclusions
This study may contribute to describing the general health status and identifying the determinants of self-rated health of managers in petroleum production enterprises in China.
The study found that the middle-age managers (ages 41-50 years in this study) with lower income and at the medium managerial level and lower-income male managers were more likely to be in poor mental health, while the female and lower-income managers in the middle age group were more likely to be in poor social health.
It will be important to take income and managerial level into consideration when designing health promotion and intervention programs for the special needs of managers, especially those of middle age, in Chinese petroleum production enterprises.
Psychological counseling is needed for the managers in the 41-to 50-year-old age group because they bear enormous burdens in both work and life, especially those who earn less and are at the medium managerial level. For female managers in the same age group, the creation of a harmonious and mutually supportive working environment will be beneficial to improve their social well-being.

Availability of data and materials
Data is available for other researchers in an unidentified form, after agreement with the research group. Ethics approval and consent to participate The study was approved by Ethics Committee of the School of Public Health, Sun Yat-sen University, and participation in this study was voluntary and anonymous. All the answers were treated strictly confidential, the procedure of this study was in accordance with ethical standards at this time.

Consent for publication
Not applicable.