Stress Perception Mediates the Relationship between Stress and Quality of Life among Chinese Police Ocers

Background Police ocers are known for working under high-stress environment, and it is widely reported that police ocers suffer from stress-related ailments which could subsequently impact their life quality. However, there is little direct research that describes the relationship between police ocers’ quality of life and stress. Current study aims to investigate police ocers’ quality of life and explore the effect of stress on life quality of police ocers. Our study also explores the effect of stress perception on the relationship between the stress and quality of life to see whether changing police ocers’ stress perception can improve their quality of life. Methods We conduct literature search on police ocers’ life quality in China, and compare the result against the general population. We also investigate 914 Chinese police ocers, measured their life quality, stress level and stress perception, and analyze the stress’ inuence on quality of life. Results The result shows that the life quality of police ocers is generally lower than the general population, and many factors, such as age, education level and gender, will inuence the quality of life. Police ocer’s life quality is negatively correlated with their stress level, and stress perception appears to mediate the relationship between the stress and quality of life. Conclusion and functions along eight subscales: physiological function (PF), Role limitations due to physical problems (RP), body pain (BP), general health (GH), vitality (VT), social function (SF), Role limitations due to emotion problems (RE), mental health (MH). Each dimension is scored by Likert's cumulative method, and scores are transformed onto a 0 to 100 scale.


Introduction
Quality of life is de ned by WHO as an individual's perception 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. Previous studies reported that depression, economic condition, health condition, cognitive function and marriage condition would in uence the elderly's quality of life (Xu, 1994;Dai, Liu, & Ma, 2003), and the quality of life of people with breast cancer correlated with social support (Sammarco, & Angela, 2001).
Besides, stress is also an in uential factor of life quality. Some studies on cancer patients indicated that quality of life was affected negatively by stress (Kreitler, Peleg, & Ehrenfeld,2010). An online study in 2014 examined the relationship between generally perceived levels of stress and the quality of life on Facebook and found that people who spent the more time on Facebook had the higher stress and lower quality of life (Bevan, Gomez, & Sparks,2014). Since police work is known for its high-stress nature (He, Zhao, & Archbold, 2002;Sarason, et al.,1980), police o cer's quality of life may be in the lower end of the spectrum. Police o cers are often exposed to some stressful events, such as confrontation, violence, traumatic incidents, and human misery (Chen, et al.,2006). Besides the stress from work, police o cers also suffer the stress from family and relationship, since they tend to have little time to deal with family issues. Lipp and Marilda (2009) investigated the levels of occupational stress and quality of life of Brazilian police o cer and found that the police o cers considered their job to be very stressful and their standard of quality of life was found to be poor. Santanu and his colleagues (2016) studied the relationship between job stress and quality of life among police personnel in India, and found that o cers were more stressed than constables, while the score of quality of life was higher in constables than o cers, which implied that policemen who had higher work stress had lower quality of life. Few studies have investigated the relationship between the stress and quality of life of Chinese police o cers, thus our study aims to investigate current situation of quality of life of police o cers in China, to compare it against the general population, and to explore the effect of stress on quality of life of Chinese police o cers. We assume that life quality of police o cers would be lower than the general population(hypothesis1), and stress would have negative effect on life quality of police o cers (hypothesis 2).
Due to the impracticality of enhancing police o cers' life quality by cutting their workloads and workderived raw stress, we investigate the relationship between stress and quality of life and try to discover another possible route. Previous study on U.S.A. adult found that high amounts of stress and the perception that stress impacts health were each associated with poor physical and mental health (Keller, Peleg, & Ehrenfeld, 2012). And according to Ellis's ABC Theory of Emotion, activating event will in uence the people's belief and then affect consequence (Ellis, 1985). Therefore, we want to explore the effect of stress perception on the relationship between the stress and quality of life. We assume that stress perception would mediate the relationship between the stress and quality of life (hypothesis 3), and we

Data analysis
According to our standards, we include 4 papers in our study. We list the data of quality of life in the tables and compare them against the norm of general population.
Study2: the relationship between stress and quality of life Participants Yiwu is a county-level city in Zhejiang province and is the largest county-level city in China, with about 1200 policemen. Questionnaires were sent out during the annual health examination of policemen, and 914 police o cers aged from 22 to 60 participated in the study voluntarily, and 900 (mean age = 38.3, SD = 9.8) completed the questionnaire thoroughly. 6 police o cers returned incomplete data and 8 refused to offer demographic data. The effective response rate of the questionnaire is 98.5%, and the response rate of entire sample is 75%.

Measure
Police stress scale Our study used the Police stress scale (Chen, & Xu, 2012) to measure the stress of police o cers. This scale has 46 items and 6 dimensions, including task-related stressor, social life stressor, power motive stressor, self-related stressor, negative emotion stressor and organization management stressor. Participates were required to judge whether the event described in item occurred to themselves. If it did not occur, it is recorded as 0. If the event occurred, the participates were asked to evaluate the impact of the event by 5-point Likert format (not affected, mild, moderate, severe, or extremely severe), and high score indicates high levels of stress. The scale has been found to have highly acceptable psychometric property (Chen, & Xu, 2012)

Data analysis
For statistical analysis, Mean and Standard Deviation (SD) are computed. Analysis of variance is used to examine the differences of stress, stress perception, and quality of life for age, education, years of service, and t-testing was used to analyze the gender difference. Analysis of variance is also used to test the effect of stress on quality of life. Mediation analysis is used to explore the relationship among stress, stress perception and quality of life. All data are analyzed with the SPSS 22.0 statistical analysis software package and Process 3.4 software package.

Current situation of police o cers' quality of life
According to the data provided by the WHO quality of life research group, the score of WHOQOL-BREF tested in Chinese people from 2000 to 2002 shows: physiological score is 61.3 ± 16.3, psychological score is 61.6 ± 13.7, social relations score is 64.6 ± 14.2, environment score is 52.9 ± 13.5. After comparison (Table 1), the result of rst article shows that the life quality of recruits of China armed police is higher than the general population. The result is well within our expectation, since the sample is consisted by new recruits who barely experienced much stress. The second article indicates that the scores of four elds of quality of life are lower in police o cer than normal people, which is in accordance with our hypothesis.    Table 3

Correlation analysis
The descriptive statistics and correlation matrix are presented in Table 7. Stress is positive correlated with stress perception, and negatively correlated with PCS and MCS. Stress perception is negatively correlated with PCS and MCS.

Testing for proposed model
The main results generated by SPSS macro PROCESS are presented in Table 8 and Table 9, which consist of two parts: mediator and dependent variable model of PCS and mediator and dependent variable model of MCS. The mediator variable model is to test the effect of stress, and the dependent variable model is to test the effects of stress, stress perception. The LLCI and ULCI of the sequence of indirect effect are used to estimate the 95% con dence interval. Shall the interval does not contain zero, mediator effect exists. As can be seen from the result showed in Table 8 and Table 9, the intervals of two models don't contain zero, which mean stress perception have mediator effect on the relationship between the stress and quality of life. As can be seen from the mediator variable model of PCS (F = 115.18, R 2 = 0.39, p < 0.01) and dependent variable model of PCS (F = 58.28, R 2 = 0.28, p < 0.01), stress positively predicts stress perception(β = 0.13, p < 0.01), stress perception negatively predicts PCS(β=-0.29, p = 0.04), stress negatively predicts PCS(β=-0.08, p < 0.001). These results indicate that stress perception partially mediates the relationship between stress and PCS (Fig. 2). And the mediator variable model of MCS (F = 115.18, R 2 = 0.39, p < 0.01) and dependent variable model of MCS (F = 65.27, R 2 = 0.30, p < 0.01) indicates that: stress positively predicts stress perception(β = 0.13, p < 0.01), stress perception negatively predicts MCS(β=-0.38, p = 0.04). These results indicate that stress perception totally mediates the relationship between stress and MCS (Fig. 3). Note. N = 900. Bootstrap sample size = 5000. LL = low limit, CI = con dence interval, UL = upper limit. Note. N = 900. Bootstrap sample size = 5000. LL = low limit, CI = con dence interval, UL = upper limit.

Discussion
Both the results of our study and previous literature indicates that life quality of police o cers are lower than normal people, which concur with our rst hypothesis. The result of analysis of relationship between stress and life quality shows that stress would affect police o cers' life quality, which is in accordance with our second hypothesis. Meanwhile, the result of mediation analysis shows that stress perception is the mediator of the relationship between stress and quality of life. It's concordant with our third hypothesis.
According to analysis of previous studies of SF-36, we nd that police o cers score lower in the dimensions of physiological function, social function and mental health, which is accordant with our expectation. In our eld experience, police o cers always have to work overtime when urgent event happens, which heavily shrinks their quality time with their families and friends. Police o cers also tend to report stress from social relationship, which negatively impacts their social function. Besides, exposing to other occupational stressful events will also affect police o cers' physiological function and mental health.
Our study nd that many one is cultural difference, the other is that female sample in our research is much smaller than male sample. Thus, the gender difference of stress and life quality in police population still requires further research.
The analysis of mediation model indicates that stress perception can partially mediate relationship between stress and MCS, and totally mediate the relationship between stress and PCS. These results mean that stress can directly in uence physical health and indirectly through the stress perception. While mental health can only be indirectly in uenced by stress through the stress perception. Since mental health is more closely related to belief and cognition, these results are within our expectation.

Declarations
Ethics approval and consent to participate: The research was approved by the institutional review boards of Zhejiang University.

Consent for publication: not applicable
Availability of data and materials: The datasets during and/or analyzed during the current study available from the corresponding author on reasonable request.
Competing interests: The authors declare that they have no competing interests Funding: There is no funding in this study.
Authors' contributions: YZ analyzed and interpreted the data and was a major contributor in writing the manuscript. CJ collected data from police o cers and revised the manuscript. JW collected the questionnaires used in research, write and revised part of the manuscript. YJ revised the manuscript. SC directed research and revised the manuscript. All authors read and approved the nal manuscript.