Influence of occupational stress and coping styles on depressive symptoms in 2,083 manufacturing workers of China

doi:10.21203/rs.3.rs-3582011/v1

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Research Article

Influence of occupational stress and coping styles on depressive symptoms in 2,083 manufacturing workers of China

https://doi.org/10.21203/rs.3.rs-3582011/v1

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Background

This study aims to investigate the influence of occupational stress and coping styles on depressive symptoms in manufacturing workers of China.

Methods

A total of 2,083 workers from two manufacturing enterprises in Beijing City and four manufacturing enterprises in Guangdong Province were selected as study subjects using judgment sampling method. The occupational stress, coping styles, and depression symptoms were accessed using the Core Occupational Stress Measurement Scale, Trait Coping Style Questionnaire and Patient Health Questionnaire Depression Scale.

Results

A total of 2,311 questionnaires were distributed, and 2,083 valid questionnaires were collected, with a valid questionnaire recovery rate of 90.1%. The average scores of occupational stress, positive coping style, negative coping style and depressive symptoms among the study subjects were 45.0, 32.0, 23.0 and 6.0, respectively. The detection rates of occupational stress and depressive symptoms were 29.5% (615/2,083) and 15.7% (327/2,083). Depressive symptoms were positively correlated with occupational stress and negative coping style (r_S were 0.351 and 0.540, respectively, and both P < 0.001), and negatively correlated with positive coping style (r_S was − 0.208, P < 0.001). Occupational stress was positively correlated with negative coping style (r_S was 0.296, P < 0.001) and negatively correlated with positive coping style (r_S was − 0.246, P < 0.001). The four dimensions of occupational stress explained 15.9% of variation in depressive symptoms (P < 0.001). The inclusion of the two dimensions of coping styles on the above basis could explain 19.3% of the variation in depressive symptoms (P < 0.001). Meanwhile, the four dimensions of occupational stress had a statistically significant effect on depressive symptoms (P < 0.05).

Conclusions

Occupational stress could directly affect the occurrence of depressive symptoms in manufacturing workers of China. Coping styles moderated the effect of occupational stress on depressive symptoms. Positive coping style could help alleviate the adverse effects of occupational stress and reduce the risk of depressive symptoms.

Manufacturing

Workers

Occupational stress

Coping style

Depression symptoms

Correlation

Influencing factor

Manufacturing was the main body of China's national economy and had played a major role in China's economic development [1]. With the gradual deepening of economic globalization and China's industrial structure adjustment, manufacturing enterprises were fiercely competitive, and they were still facing problems such as industrial basic capabilities and competitiveness to be improved [2, 3]. Affected by the characteristics of its industry, manufacturing workers had been carrying out repetitive, monotonous and fast-paced operations for a long time, long working hours and maintaining the same working posture, dense assembly lines, crowded working space, etc., resulting in various physical and mental health problems of workers, which in turn lead to absenteeism, production accidents and reduced working capacity, bringing heavy economic burden to enterprises and society [4, 5]. The construction of a manufacturing power had also put forward higher skill requirements for front-line workers in the manufacturing industry [6]. Studies had shown that manufacturing workers had a high incidence of occupational stress, depressive symptoms and other mental illnesses [7, 8], which had become a public health problem that seriously endangers the health of occupational groups in China.

Occupational stress, also known work stress and work pressure, referring to the physical and psychological reactions that occur when the requirements of an individual's job position do not match the individual's abilities, resources, or needs, and if persistent, could lead to physical and mental health impairment [9]. According to the World Health Organization, occupational stress had become a worldwide epidemic, and labor losses caused by occupational stress had become among the top 10 in the burden of occupation-related diseases. Depressive symptoms were negative emotional experiences, persistent and severe depressive symptoms could lead to impaired social ability, depressive symptoms in the workplace would not only have a serious negative impact on employees' psychology and behavior, but also lead to economic losses such as reduced productivity, absenteeism, and personnel turnover [10, 11]. China's occupational population lacks early identification methods for occupational psychological disorders at present, and the proportion of patients receiving early and effective intervention or even visiting medical and health institutions was very small. Cross-sectional and cohort studies of occupational population had found that occupational stress was closely associated with the occurrence of depressive symptoms [12, 13]. Once the occupational population with depressive symptoms failed to receive effective intervention and treatment, and with the combination of adverse emotions such as occupational stress, they were more likely to develop more serious psychological disorders or mental diseases such as anxiety disorders and emotional disorders [14]. As an internal coping resource, coping styles referred to the coping strategies or methods that people adopt to changes in their internal and external environment and the emotional distress along with them [15]. Based on trait theory, the coping styles emphasizes the prediction of individual coping styles through quantifiable personality traits, which was divided into two types: positive coping style and negative coping style. Positive coping style could help alleviate the adverse effects of occupational stress and maintain physical and mental health. Negative coping style was not conducive to alleviating negative emotions such as occupational stress, and was more likely to lead to mental illness [16].

Most workers′ occupational careers account for more than half of their life cycle, and only when the health of manufacturing workers was guaranteed can we provide solid guarantee and support for the vigorous development of China's manufacturing industry [17]. Therefore, this study aims to understand the mental health of manufacturing workers and analyze the effects of occupational stress and coping styles on depressive symptoms. The clarification of this relationship is conducive to the implementation of psychological interventions for Chinese manufacturing workers, which is of great significance for promoting the physical and mental health of this population, ensuring the efficiency of China's manufacturing industry, and promoting sustainable and healthy economic development.

Subjects

Using the judgment sampling method, workers from two manufacturing enterprises in Beijing City and four manufacturing enterprises in Guangdong Province were selected as the research subjects from June to October 2020. Inclusion criteria: i) voluntary participation in the survey and signing of informed consent. ii) Aged more than 18 years old. iii) Working in the position for continuous half a year or more. iv) The questionnaire information was complete. Exclusion criteria: i) long-term sick leave. ii) Have a history of mental illness, or have taken psychotropic drugs during one week before the investigation.

Ethics approval and consent to participate

The data of this study are from the Special Investigation Project on Occupational Disease Hazards of Key Populations of the Occupational Health Institute of the Chinese Center for Disease Control and Prevention (No. 131031109000190002), which is undertaken by the Institute of Occupational Health and Poisoning Control of the Chinese Center for Disease Control and Prevention and jointly completed by multiple provincial (municipal) cooperative units.

Study design and population

The Basic Situation Questionnaire designed by our research group was used to investigate the basic situation of the research subjects, including sociodemographic characteristics (gender, age, education level, marital status, personal monthly income) and job characteristics (length of service, average weekly working hours, job position and shift work of the post).

Occupational stress

The Core Scale of Occupational Tension Measurement developed by our research group was used to evaluate the occupational stress status of the research subjects [18]. The scale includes four dimensions: social support, organization and reward, demand and effort, and autonomy, with 5, 6, 4 and 2 questions respectively. A Likert score of 5 points was used, with a score of 1.0 indicating "strongly disagreeing" and 5.0 indicating "strongly agreeing". Among them, the dimensions of social support and autonomy were inversely scored, and the total score was calculated after conversion according to 6－actual score. The total score of occupational stress was calculated according to the formula "occupational stress score=(30.0－social support dimension score)＋organization and reward dimension score＋demand and effort dimension score＋(12.0－autonomy dimension score)", and the total score≥50.0 points was judged to be the existence of occupational stress, and the higher the score, the more serious the occupational stress [19]. In this study, the cumulative variance contribution rate of the common factor was 62.1%, the goodness-of-fit index (GFI), comparative fit index (CFI) and root mean square error of approximation (RMSEA) were 0.904, 0.912 and 0.079, respectively, and the Cronbach′s α coefficients of the aggregate table and four dimensions were 0.794, 0.906, 0.787, 0.719 and 0.808, respectively [18]. The results showed that the scale had good reliability and validity, and could be used as a measurement and evaluation tool for the occupational tension of manufacturing workers in China.

Coping styles

The Trait Coping Style Questionnaire (TCSQ) was used to evaluate the individual's relatively stable coping styles with certain personality tendencies to different events in life [20]. The scale includes two dimensions, positive coping style and negative coping style, with 10 items in each dimension. Among them, the positive coping items include items of 1, 3, 5, 8, 9, 11, 14, 15, 18 and 20, and the negative coping items include items of 2, 4, 6, 7, 10, 12, 13, 16, 17 and 19. A Likert score of 5 points, with a score of 1.0 being "definitely not" and 5.0 being "definitely yes". The cumulative score of each dimension was calculated, and a higher score in the dimension of positive coping style indicated a higher degree of positive coping, and a higher score in the dimension of negative coping style indicated a higher degree of negative coping [20]. The Cronbach′s α coefficients of the total scale and the two dimensions were 0.861, 0.878 and 0.889, respectively. The results showed that the scale had good reliability and validity, and could be used as a measurement and evaluation tool for the coping style of manufacturing workers in China.

Depressive symptoms

The Chinese edition of the Patient Health Questionnaire Depression Scale (PHQ-9) was used to evaluate the depressive symptoms of the study subjects [21]. This scale was a simple and effective tool for diagnosing and assessing the severity of depression [22]. The scale included nine depressive symptoms and one moderating variable, i.e., to investigate impairment condition of social functioning, for a total of 10 items. Using a Likert 4-point score, based on the frequency of symptoms over the past two weeks, 0.0 means "not at all" and 3.0 means "always". A score of≥10.0 indicates the presence of depressive symptoms, with higher scores indicating a greater degree of depressive symptoms [23]. The Cronbach's α coefficient on the scale in this study was 0.913, indicating that the scale had good reliability.

Quality control

The research group formulated a unified quality control plan, established a quality control network composed of national, provincial and survey site levels, and clarified the responsibilities at all levels, including: i) Pre-investigation: the project team was responsible for organizing project technical backbone training, communicating with the unit under investigation, clarifying the purpose and significance of the investigation, obtaining leadership support, and ensuring the smooth progress of the investigation. We carried out pre-investigation work, corrected problems in a timely manner, and improved questionnaires and programs according to the results of pre-investigation to ensure the scientific and rigorous nature of the investigation work. We uniformly trained investigators on project design, precautions for filling out questionnaires, on-site investigation skills, etc. ii) Mid-investigation: we organized relevant experts to carry out on-site technical guidance, and arranged special personnel to be responsible for the on-site organization and implementation of the project. While distributing questionnaires on site, investigators were responsible for explaining to the research subjects the purpose of the survey and the precautions for filling out the questionnaire. The study subjects filled in the questionnaire in the form of anonymous self-filling questionnaires which were collected on the spot. We established a questionnaire review system for investigators, quality controllers and investigation leaders, and conducted secondary investigations for unqualified questionnaires. iii) Post-survey: the collected questionnaires were examined the internal logic between variables and questionnaires with a missing degree of more than 10.0% were excluded. The questionnaire adopts EpiData 3.1 software for double data entry, and strives for good data quality. We aslo standardized the source control of missing data during data cleaning, and the processing of missing data (filling or deletion).

Statistical analysis

All statistical tests were bilateral (α=0.05). Counting data was expressed in frequency (n) and composition ratio (%). The measurement data were subject to the normal distribution by the normality test, and the mean comparison between the two groups was described by the two-independent sample t-test, and the mean comparison between multiple groups was carried by one-way ANOVA. The measurement data were described by the median (M) and 0-100^th percentile (P₀-P₁₀₀) or the 25^th and 75^th percentiles (P₂₅, P₇₅) if they didn’t follow a normal distribution after the normality test; the Mann-Whitney U test was used for the M-comparison between the two groups, and the Kruskal-Wallis H test was used for the M-comparison between the multiple groups. Spearman rank correlation analysis was used to analyze the correlation between occupational stress, coping styles and depressive symptoms, and the Spearman rank correlation coefficient (r_S) was calculated. Hierarchical regression analysis was used to analyze the effects of occupational stress and coping styles on depressive symptoms (forced entry method). Taking the depressive symptom score as the dependent variable, the demographic characteristic variable was introduced as the control variable in the first layer. The second layer introduced four dimensional variables of occupational tension, namely social support, organization and return, demand and giving, and autonomy. The third layer introduced two dimensional variables of coping styles, namely positive coping style and negative coping style. We assessed the extent to which the dimensions of occupational stress and coping styles were associated with depressive symptoms. All data were statistically analyzed using SPSS 21.0 software.

Basic information

A total of 2,311 questionnaires were distributed and 2,083 valid questionnaires were recovered, with a recovery rate of 90.1%. The age of the study subjects was 19-60 (35±8) years, and the length of service in this position was 4.1 (2.3, 8.5) years; the distribution of different demographic characteristics is shown in Table 1.

Comparison of occupational stress, coping styles and depression symptom scores

The total scores of occupational stress M (P₂₅, P₇₅) was 45.0 (40.0, 51.0), and the scores of social support, organization and reward, demand and effort, and autonomy were 20.0 (17.0, 21.0), 15.0 (12.0, 18.0), 12.0 (10.0, 14.0) and 4.0 (4.0, 6.0), respectively, and the detection rate of occupational stress was 29.5% (615/2,083). The scores of positive coping style and negative coping style M (P₂₅, P₇₅) were 32.0 (28.0, 36.0) and 23.0 (19.5, 28.0), respectively. The depressive symptom score M (P₂₅, P₇₅) was 6.0 (3.0, 8.0), and the detection rate of depressive symptoms was 15.7% (327/2,083). The scores of occupational stress, coping styles and depressive symptoms in different demographic groups are shown in Table 1.

Table 1 Comparison among the scores of occupational stress, coping styles and depression symptoms in different demographic groups

Groups	Number	Proportion (%)	Occupational stress [M(P₂₅,P₇₅)]	Coping styles[M(P₂₅,P₇₅)]		Depression symptoms [M(P₂₅,P₇₅)]
Groups	Number	Proportion (%)	Occupational stress [M(P₂₅,P₇₅)]	Positive coping style	Negative coping style	Depression symptoms [M(P₂₅,P₇₅)]
Gender
Male	1,131	54.3	45.0(40.0,51.0)	32.0(28.0,36.0)	23.0(20.0,28.0)	7.0(3.0,9.0)
Female	952	45.7	45.0(40.0,51.0)	32.0(28.0,36.0)	23.0(19.0,28.0)	6.0(2.0,8.0)
Age
19-25	294	14.1	45.0(40.0,51.0)	32.0(28.0,36.0)	23.0(20.0,29.0)	7.0(3.0,9.0)
26-30	446	21.4	44.0(39.0,50.0)	32.0(28.0,36.0)	23.0(20.0,28.0)	7.0(3.0,9.0)
31-40	836	40.1	45.0(40.0,51.0)	31.0(28.0,36.0)	24.0(20.0,28.0)	7.0(3.0,9.0)
41-50	419	20.1	46.0(41.0,51.0)	32.0(28.0,37.0)	23.0(19.0,27.0)	6.0(2.0,8.0)^abc
51-60	88	4.2	46.0(41.5,52.0)	32.0(29.0,36.0)	23.0(19.5,28.0)	6.0(2.0,8.0)
Education level
Junior high school and below	854	41.0	46.0(41.0,51.0)	32.0(28.0,36.0)	23.0(19.0,28.0)	6.0(2.0,8.0)
High school/Technical secondary school	980	47.0	45.0(39.0,50.0)^d	32.0(28.0,36.5)	23.0(20.0,28.0)	7.0(3.0,9.0)
College degree and above	249	12.0	44.0(40.0,50.0)	31.0(28.0,36.0)	23.0(20.0,28.0)	7.0(3.0,9.0)
Marital status
Unmarried/Divorced/Widowed	537	25.8	45.0(40.0,51.0)	32.0(27.0,36.0)	24.0(20.0,29.0)	7.0(3.0,9.0)
Married cohabitation	1,344	64.5	45.0(40.0,51.0)	32.0(28.0,36.0)	23.0(19.0,28.0)	6.0(2.0,8.0)^f
Married separation	202	9.7	45.0(40.0,50.0)	32.0(28.0,37.0)	24.0(20.0,28.0)	6.5(3.0,9.0)
Personal monthly income
＜¥ 3000	301	14.5	45.0(40.0,50.0)	32.0(27.0,36.0)	23.0(18.0,28.0)	6.0(2.0,8.0)
¥ 3000-＜¥ 5000	871	41.8	46.0(40.0,51.0)	32.0(28.0,36.0)	23.0(20.0,29.0)	6.0(3.0,9.0)
¥ 5000-＜¥ 7000	664	31.9	46.0(40.0,51.0)	32.0(28.0,36.0)	23.0(19.0,28.0)	6.0(3.0,8.0)
≥¥ 7000	247	11.8	42.0(37.0,48.0)^ghi	32.0(29.0,37.0)	23.0(20.0,27.0)	7.0(4.0,9.0)^g
Length of service (years)
0.5-＜2.0	364	17.5	45.0(40.0,50.0)	31.0(28.0,36.0)	23.0(19.0,28.0)	6.0(3.0,8.0)
2.0-＜5.0	792	38.0	46.0(40.0,51.0)	32.0(28.0,36.0)	23.0(19.0,28.0)	7.0(3.0,9.0)
5.0-＜10.0	492	23.6	45.0(39.2,50.0)	32.0(28.0,36.0)	23.5(20.0,29.0)	7.0(3.0,8.0)
10.0-35.7	435	20.9	45.0(40.0,50.0)	32.0(29.0,37.0)	23.0(20.0,28.0)	7.0(2.0,9.0)
Average weekly working hours
≤40	198	9.5	44.0(39.0,51.0)	32.0(28.0,37.0)	23.0(18.0,28.0)	6.0(2.0,8.0)
41-48	549	26.4	45.0(40.0,50.0)	32.0(28.0,36.0)	23.0(19.0,28.0)	6.0(3.0,8.0)
49-58	451	21.6	44.0(40.0,51.0)	31.0(28.0,37.0)	23.0(20.0,28.0)	6.0(3.0,8.0)
59-66	521	25.0	46.0(41.0,50.0)	32.0(28.0,36.0)	23.0(19.0,28.0)	6.0(3.0,8.0)
≥67	364	17.5	46.0(40.0,51.0)	31.0(28.0,35.0)	24.0(20.0,29.0)^j	7.0(4.0,9.0)^jkl
Job position
Assembly line	1,322	63.5	46.0(41.0,52.0)	32.0(28.0,36.0)	23.0(19.0,28.0)	6.0(3.0,8.0)
Non-assembly line	761	36.5	43.0(39.0,49.0)	32.0(28.0,37.0)	23.0(20.0,28.0)	7.0(3.0,9.0)
Shift work
No	1,602	76.9	45.0(40.0,51.0)	32.0(28.0,36.0)	23.0(19.0,28.0)	6.0(3.0,8.0)
Yes	481	23.1	45.0(39.0,51.0)	32.0(28.0,37.0)	24.0(21.0,29.0)	7.0(3.0,9.0)
Z₁ value			－0.263	0.758	－1.262	－1.995
p₁ value			0.793	0.448	0.207	0.046
H₂ value			11.089	3.629	6.988	15.443
p₂ value			0.026	0.458	0.137	0.004
H₃ value			10.424	1.344	1.132	6.458
p₃ value			0.005	0.511	0.568	0.040
H₄ value			0.732	4.298	7.265	7.796
p₄ value			0.693	0.117	0.026	0.020
H₅ value			36.863	1.089	4.889	7.982
p₅ value			＜0.001	0.780	0.180	0.046
H₆ value			4.260	5.410	2.334	1.361
p₆ value			0.235	0.144	0.506	0.715
H₇ value			9.859	1.594	11.141	13.970
p₇ value			0.043	0.810	0.025	0.007
Z₈ value			－7.071	1.140	0.702	1.091
p₈ value			＜0.001	0.254	0.483	0.275
Z₉ value			－0.839	1.301	3.209	4.125
p₉ value			0.401	0.193	0.001	＜0.001

Note: Z₁ and P₁, H₂ and P₂, H₃ and P₃, H₄ and P₄, H₅ and P₅, H₆ and P₆, H₇ and P₇, Z₈ and P₈, Z₉ and P₉ were the statistical results of the score comparison of different gender, age, education level, marital status, personal monthly income, length of service, average weekly working hours, job position and shift work groups. Compared with the 19-25 years old group, ^aP<0.01. Compared with the 26-30 years old group, ^bP<0.05. Compared with the 31-40 years old group, ^cP<0.05. Compared with the group with education level of junior high school and below, ^dP<0.01. Compared with the high school/technical secondary school group, ^eP<0.05. Compared with the unmarried/divorced/widowed group, ^fP<0.05. Compared with personal monthly income of less than ¥ 3000, ^gP<0.05. Compared with personal monthly income of ¥ 3000-＜¥ 5000, ^hP<0.01. Compared with personal monthly income of ¥ 5000-＜¥ 7000, ⁱP<0.01. Compared with average weekly working hours of ≤40 hours, ^jP<0.05. Compared with average weekly working hours of 41-48 hours, ^kP<0.05. Compared with average weekly working hours of 59-66 hours, ^lP<0.05.

Correlation analysis among occupational stress, coping styles and depressive symptoms

Depressive symptoms were positively correlated with occupational stress and negative coping style (r_S were 0.351 and 0.540, respectively, and both P<0.001), negatively correlated with positive coping style (r_S was －0.208, P<0.001). Occupational stress was positively correlated with negative coping style (r_S was 0.296, P<0.001), and negatively correlated with positive coping style (r_S was －0.246, P<0.001). Among them, depressive symptoms were positively correlated with the organizational and reward, demand and effort dimensions of occupational stress and negative coping style (r_S were 0.299, 0.266 and 0.540, respectively, and all P<0.001), and negatively correlated with the social support dimensions of occupational stress and positive coping styles (r_S were －0.254 and －0.208, respectively, and both P<0.001). Positive coping style was positively correlated with social support and autonomy of occupational stress (r_S were 0.250 and 0.061, respectively, and both P<0.01), and negatively correlated with the dimensions of organization and reward, demand and effort of occupational stress (r_S were －0.136 and －0.107, respectively, and both P<0.001). Negative coping style was positively correlated with the dimensions of organization and reward, demand and effort of occupational stress (r_S were 0.298 and 0.239, respectively, and both P<0.01), and negatively correlated with the social support dimension of occupational stress (r_S was －0.160, P<0.001).

Hierarchical regression analysis on the effect of occupational stress and coping styles on depressive symptoms

Hierarchical regression analysis was carried out by taking the depressive symptom score as the dependent variable, and the demographic characteristic variables, occupational stress and coping styles dimension scores with statistical significance for depressive symptoms in Table 1 as independent variables. In the first layer, the demographic characteristic variables were included as the control variables, and the results showed that the effect of shift work on depressive symptoms was statistically significant (P<0.05). In the second layer, the four dimensions of occupational stress were included in the equation, and the results showed that the effects of these four dimensions on depressive symptoms were statistically significant (all P<0.01), explaining the 15.9% of variation (P<0.001) in depressive symptoms, suggesting that occupational stress can directly affect depressive symptoms. In the third layer, the two dimensions of coping styles were included in the equation, and the results showed that the effects of these two dimensions on depressive symptoms were statistically significant (both P<0.001), which could explain 19.3% of variation in depressive symptoms (P<0.001), meanwhile the effects of four dimensions of occupational stress on depressive symptoms were statistically significant (P<0.05). See Table 2.

Table 2 Hierarchical regression analysis results of the effects of occupational stress and coping styles on depression symptoms among research subjects

Variables	Layer 1			Layer 2			Layer 3
Variables	β value	t value	P value	β value	t value	P value	β value	t value	P value
Gender	－0.004	－0.159	0.874	0.023	0.933	0.351	0.014	0.650	0.516
Age	－0.039	－1.517	0.129	－0.053	－2.217	0.027	－0.033	－1.560	0.119
Education level	0.049	1.908	0.056	0.045	1.918	0.055	0.044	2.125	0.034
Marital status	－0.021	－0.848	0.397	－0.022	－0.962	0.336	－0.012	－0.604	0.546
Personal monthly income	0.004	0.139	0.889	0.052	2.023	0.043	0.031	1.369	0.171
Average weekly working hours	0.033	1.328	0.184	－0.005	－0.227	0.821	－0.006	－0.286	0.775
Shift work	0.056	2.222	0.026	0.083	3.512	＜0.001	0.064	3.104	0.002
Occupational stress
Social support				－0.239	－11.067	＜0.001	－0.136	－6.809	＜0.001
Organization and reward				0.168	6.628	＜0.001	0.056	2.491	0.013
Demand and effect				0.174	7.101	＜0.001	0.100	4.615	＜0.001
Autonomy				－0.068	－3.058	0.002	－0.051	－2.606	0.009
Coping styles
Positive coping style							－0.146	－7.732	＜0.001
Negative coping style							0.480	24.958	＜0.001
F value		3.834^a			39.200^a			91.401^a
R²value		0.013			0.172			0.365
Adjusted R²value		0.009			0.168			0.361
Increment of R² value					0.159			0.193

Note: β is normalized partial regression coefficients, R² is coefficients of determination. In the assignment of independent variables, gender: male=1, female=2. Age: 19-25 years old=1, 26-30 years old=2, 31-40 years old=3, 41-50 years old=4, 51-60 years old=5. Education level: junior high school and below=1, high school/technical secondary school=2, college or above=3. Marital status: unmarried/divorced/widowed=1, married cohabitation=2, married separation=3. Personal monthly income: <¥ 3000=1, ¥ 3000-<¥ 5000=2, ¥ 5000-<¥ 7000=3, ≥¥ 7000=4. Average weekly working hours : ≤40 hours=1, 41~48 hours=2, 49~58 hours=3, 59~66 hours=4, ≥67 hours=5. Shift work: no=1, yes=2. The scores of various dimensions of occupational stress and coping styles are continuous variables and not assigned values. ^aP<0.001. Blank items indicate that there is no data for this item.

Most of China's manufacturing workers were engaged in repetitive and uncreative work, and with the upgrading of the industrial structure, higher requirements had been put forward for the quality and technology of this population, coupled with the low sense of social identity and low welfare benefits, the mental health problems of this group had been attracting attention [24-26]. As a simple and effective screening scale for depression, PHQ-9 was widely used in the screening of depressive symptoms in China's occupational population. PHQ-9 was used to evaluate the depression of employees of 34 gene sequencing companies in China, and the results showed that 427 employees had a depressive symptom score of M (P₂₅, P₇₅) of 8.0 (6.0, 11.0) and a depressive symptom detection rate of 33.5% (143/427) [27]. In the early investigation of the depression of assembly line employees in China's electronics manufacturing service industry, the score of depressive symptoms was 8.0 (5.0, 10.0), and the detection rate of depressive symptoms was 31.0% (2,623/8,456) [28]. In this study, 2,083 Chinese manufacturing workers scored M (P₂₅, P₇₅) with depressive symptoms of 6.0 (3.0, 8.0), and the detection rate of depressive symptoms was 15.7%. Numerous studies had shown that occupational stress had a significant positive effect on depression, i.e., the higher the degree of occupational stress, the greater the likelihood of depressive symptoms [29,30]. The detection rate of depressive symptoms in the subjects of this survey was lower than that of the results of other populations mentioned above, which might be related to the different sample sizes and the types of work of the study subjects. On the other hand, it might be that our research group had implemented the optimized "333" model of occupational stress three-level prevention intervention for manufacturing workers in recent years [31], and the reduction of occupational stress level could reduce the risk of depressive symptoms.

In this study, the depressive symptoms of 2,083 manufacturing workers in China were positively correlated with occupational stress and negative coping style (r_S were 0.351 and 0.540, respectively, and both P<0.001) and negatively correlated with positive coping style (r_S was －0.208, P<0.001), while occupational stress was positively correlated with negative coping style (r_S was 0.296, P<0.001) and negatively correlated with positive coping style (r_S was －0.246, P<0.001). These suggested that occupational stress and negative coping style were risk factors for the occurrence of depressive symptoms, and positive coping style was a protective factor for reducing the occurrence of occupational stress and depressive symptoms. The results indicated that the higher the level of occupational stress and the more negative the coping style of manufacturing workers, the higher the risk of depressive symptoms. Among them, depressive symptoms were positively correlated with the dimensions of organization and reward, demand and effort of occupational stress (r_S were 0.299 and 0.266, respectively, and both P<0.001), and negatively correlated with the dimension of social support of occupational stress (r_S was －0.254, P<0.001). It showed that organization and reward, demand and effort were risk factors for the occurrence of depressive symptoms, and social support was a protective factor for reducing the occurrence of depressive symptoms. The results showed that the more promising and the better the job prospects, the higher the work requirements and level of effort required, the higher the expectations for the work, and the more likely they were to develop depressive symptoms [27]. Social support from leaders, co-workers, and family members could help reduce the risk of depressive symptoms [32-33].

In order to further clarify the effects of occupational stress and coping styles on depressive symptoms, this study adopted hierarchical regression analysis method, and first includes demographic characteristic variables with statistical significance of depressive symptoms as control variables, and the results showed that the influence of work system on depressive symptoms was statistically significant (P<0.05). Then, the four dimensions of occupational stress were also included in the equation, and the results showed that these four dimensions explained 15.9% variation of depressive symptoms (P<0.001), suggesting that occupational stress could directly affect depressive symptoms. Finally, the two dimensions of coping styles were included in the equation, and the results showed that these two dimensions of coping styles had statistical significance in their effects of depressive symptoms (P<0.001), which explained 19.3% of the variation in depressive symptoms (P<0.001), meanwhile the four dimensions of occupational stress on depressive symptoms were statistically significant (P<0.05). It suggested that coping styles had a moderating effect in the effect of occupational stress on depressive symptoms. Specifically, differences in coping styles in the same stress environment would directly affect the degree of impact of individual occupational stress on depressive symptoms. Positive coping style was the ability of individuals to regulate their own psychological conditions, which was conducive to improving personal psychological level. When workers were facing pressure from their job, cultivating positive coping ability had a positive effect on reducing occupational tension and reducing the occurrence of depressive symptoms. Conversely, manufacturing workers who tended to adopt negative coping methods would easily activate their negative self-perception and produce negative psychological experiences, which in turn increased the risk of depressive symptoms [34]. Therefore, when the working environment could not be changed and improved in the short term, manufacturing workers should be encouraged and supported to adopt more positive coping methods, such as exercise intervention and mindfulness stress reduction [35-37], to alleviate the adverse effects caused by occupational stress, and to help them reduce negative coping styles through strengthening psychological training, so as to reduce the negative impact of occupational stress on depressive symptoms.

There were certain limitations in this study: i) the study subjects were only from manufacturing enterprises in Beijing City and Guangdong Provinces, and the samples were poorly representative. ii) The companies selected in this study were longitudinal study subjects, and psychological interventions had been taken on them in recent years, which may limit the generality of the results to a certain extent. iii) This study was a cross-sectional survey, and it was not possible to speculate about the causal relationship between variables. Subsequently, a multi-stage stratified cluster sampling method would be used to expand the scope and sample size of the study to improve the generalization and representativeness of the results.

Acknowledgments

The authors would like to express their sincere gratitude to all field workers and participants of this study.

Authors’contributions

XYL designed and wrote the manuscript. HQC analyzed and interpreted the findings, co-authored the manuscript. XQL, MQH and YG collected data and revised the paper. XML, JBC and SL designed, reviewed, and revised the manuscript and approved the final manuscript as submitted. All authors have read and approved the final manuscript.

Funding

This study was supported by the Central Financial Project of Occupational Health Institute, Chinese Center for Disease Control and Prevention (grant number 131031109000160008).

Availability of data and materials

Original data are available on reasonable request. These were stored on password-protected computers at the National Institute of Occupational Health and Poison Control, Chinese Center for Disease Control and Prevention, Beijing, China. Readers who wish to gain access to the data can write to the corresponding author.

Ethics approval and consent to participate

The study protocol was approved by the Medical Ethics Committee of the National Institute of Occupational Health and Poison Control (Code No. NIOHP201914). All participants gave written informed consent before recruited into the study.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

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Influence of occupational stress and coping styles on depressive symptoms in 2,083 manufacturing workers of China

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