How does social security affect people’s subjective wellbeing in China? A chain mediation model

: We utilize data from 2017CSS to explore factors related to people’s subjective wellbeing (SWB). Employing statistical analysis software, we test the chain mediation effect among social security, social fairness, social trust, and SWB. The results show that social security has a direct positive e ffect on people’s SWB (β = 0.481, p <0.001). Social security also indirectly influences people’s SWB through social fairness and social trust. High quality of social security can enhance the degree of social fairness thereby increasing the level of social trust, finally contributing to higher levels of SWB in China. The total effect of SWB explained is 49% in the chain mediation model. Based on the results, contributions and limitations are discussed in this paper. Abstract: We utilize data from 2017CSS to explore factors related to people’s subjective wellbeing (SWB). Employing statistical analysis software, we test the chain mediation effect among social security, social fairness, social trust, and SWB. The results show that social security has a direct positive effect on people’s SWB (β = 0.481, p <0.001). Social security also indirectly influences people’s SWB through social fairness and social trust. High quality of social security can enhance the degree of social fairness thereby increasing the level of social trust, finally contributing to higher levels of SWB in China. The total effect of SWB explained is 49% in the chain mediation model. Based on the results, contributions and limitations are discussed in this paper. Abstract Abstract: We utilize data from 2017CSS to explore factors related to people ’ s subjective wellbeing (SWB). Employing statistical analysis software, we test the chain mediation effect among social security, social fairness, social trust, and SWB. The results show that social security has a direct positive effect on people ’ s SWB (β = 0.481, p <0.001). Social security also indirectly influences people ’ s SWB through social fairness and social trust. High quality of social security can enhance the degree of social fairness thereby increasing the level of social trust, finally contributing to higher levels of SWB in China. The total effect of SWB explained is 49% in the chain mediation model. Based on the results, contributions and limitations are discussed in this paper.

Government of the People's Republic of China, 2017). The government exerts effective social management and services to ensure the speed and quality of social development and improve people's life satisfaction, which also facilitates to boost the government's credibility (Liu et al., 2020). The "14th Five-Year Plan" in China outlines the integration of the social security system with public services, employment, income distribution, the rights and interests of disadvantaged groups, and grassroots social governance, it endows social security a crucial function to enhance people's livelihoods and well-being. It turns out that social security is indispensable for maintaining social fairness and justice and promoting happiness in life. Thus, we would like to answer the following questions. How does social security play a role in people's wellbeing? What positive social influence will it have? Whether the social security can indirectly influence citizens' SWB through certain mediating factors? And the specific path is worth exploring.

Social security and SWB
Maslow's need hierarchy theory believes that survival needs are the lowest-level needs of human beings. Only when survival is guaranteed and satisfied, they will pursue higher-level needs, for example, self-worth (Maslow, 1943). Social security is the key to meeting the basic material needs of citizens, which contributes to social development (Wahba & Bridwell, 1976). Social security in China is the state or the government through the redistribution of national income to achieve the goal of meeting citizens' basic living needs. The social security system mainly comprises social insurance, social assistance, preferential social treatment, and social welfare in various fields (Lu, 2013). A central role of social security is to provide support for disadvantaged groups so that they can obtain material security, such as Pension Insurance (Ng et al., 2017;Jiang & Chi, 2019), Medical Security (Bayram et al., 2012;Mao et al., 2018), Housing Security (Zumbro, 2014;Winston, 2017), Employment Security (Gorry et al., 2018;Tang et al., 2018), and urban and rural subsistence allowances (Ding et al., 2017;Wong et al., 2006). High-quality social security services can mitigate these negative influences (e.g., life stress, depression) caused by social problems by meeting basic needs to improve citizens' SWB (Böhnke, 2008;. For example, a study using panel data in the US and Europe conducted by Kapteyn and Zamarro found that retirement may increase the risk of depression for Americans and Europeans. However, this risk is likely to be reduced through the Social Security pension. Because social welfare funds can alleviate post-retirement economic stress and improve their SWB (Altun & Yazici, 2015;Kapteyn & Zamarro, 2013). The data for a study from the Centers for Disease Control and Prevention's Behavioral Risk Factor Surveillance System 2010 survey showed that health insurance is significantly associated with wellbeing. Due to medical insurance coverage, the pressure of seeking medical help can be alleviated as well as the physical health can be in good conditions. It causes higher life wellbeing (Tran et al., 2016). Relevant studies in China also displayed that social security has a direct effect on people's lives. For example, Abruquah et al. (2019) used data from CHRLS for analysis. The empirical results depicted that enjoying benefits from the public pension scheme generally enhances life satisfaction, such as Enterprise Employee Basic Pension, Government and Institution Pension, and Urban-Rural Social Pension Scheme. And Health Insurance and other social security systems provide the elderly with self-sufficiency to reduce their life burden, which makes them less dependent on their children.
This greatly improves their life satisfaction (Ding et al., 2017;Yang & Hanewald, 2020).  utilized a combination of propensity score matching (PSM) and difference-in-difference (DID) methods to examine the relationship between participation in the rural Minimum Livelihood Guarantee program (Dibao) and life satisfaction levels of recipients in China, their empirical evidence suggested that welfare programs such as rural Dibao can help improve recipients' SWB, because it gives them material support and financial support (Gao & Zhai, 2017). However, it is not enough to explore the overall situation of social security in China. Based on the above, this study proposes Hypothesis 1.
Social security has a positive effect on people's SWB in Chinese context, namely, higher quality of social security is associated with higher levels of people's SWB.

Social fairness and social trust
Fairness is a significant concept in ethics, politics, and sociology. Social fairness, which includes both equality and justice, is based on equality but is not synonymous (Chen et al., 2019). Justice judgment theory assumes that an individual's perception of fairness is based on several rules rather than on a single rule, including distribution rules and procedural rules. And the former is defined as the individual's belief that it is fair and appropriate for penalties, rewards, or resources to be distributed in terms of certain criteria. The latter is defined as an individual's belief that allocative procedures which satisfy certain criteria are fair and appropriate (Leventhal, 1980). Social trust refers to subject confidence in individuals or institutions, namely, generalized trust measured in accordance with interpersonal trust and special trust measured in accordance with institutional trust (Leung et al., 2013) .   1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64  65 According to fairness heuristic theory, when the overall sense of fairness is formed, people will regard it as enlightening information to guide and explain the related fairness information that they encounter subsequently. This overall sense of fairness will affect people's attitudes, emotions, and behaviors later on. In this way, the sense of fairness is used as an inspiration, linked to trust, cooperation, acceptance of authority and rules, etc. (Lind, 2001;Jones & Martens,2009). As far as social development is concerned, both fairness and trust are indispensable factors. They can complement each other and are of great significance for building a harmonious and orderly society.
The relationship between social fairness and social trust has been noticed in early literatures, they believed that fairness is the foundation of trust, and trust is formed when social fairness is felt (Brockner, 1996;Brugman et al., 2016;Van den Bos et al., 1998). On the one hand, social fairness perception can significantly enhance confidence in government, while unequal social distribution will cause the government to lose trust in the people. The reduction in social trust is likely to make the entire country fall into a vicious circle hindering social progress (You, et al., 2012;Zhao & Yu, 2017).
On the other hand, social fairness also contributes to interpersonal trust. Fairness of outcomes obtained and resource allocations can strengthen the individual's sense of social belonging, which will not only stimulate personal motivation and their talents to contribute to social development, but will also enhance an individual's social acceptance and social trust perception (Valcke et al., 2020). Unfairness will also hinder social interaction and decline trust and trustworthiness between people. This social environment is closely related to poor human wellbeing (Fehr et al., 2020).
For example, the study conducted by Zmerli and Castillo found that in Latin America, both income inequality and distributive unfairness are associated with lower levels of political trust (Zmerli & Castillo, 2015). This may endanger social stability and decrease the level of SWB. For special groups, procedural fairness is of great significance to their survival. Social trust is able to be improved because fairness can reduce discrimination and prejudice and make them feel social tolerance (Dierckx et al., 2021). Zhang and Zhou (2018) found that social justice has a statistically positive impact on social trust, regardless of distributive or procedural justice. It reflects respect for individuals. And public cooperation intention is likely to be consolidated by social trust. Institutional fairness can ensure the fairness of rights and interests by narrowing the gaps between different groups, which improves social integration and tolerance as well as social trust (Ziller, 2017). Not only will it enlarge people's willingness to work and engagement, but it will also enhance political support and acceptance. Therefore, maintaining social fairness and justice is positive for social development and stability (Gobena & Van Dijke, 2017;Sharma & Yadav, 2018;Zhang, 2017). To examine in depth the relationship between social fairness and social trust in China, this study proposes Hypothesis 2. Social fairness can positively predict social trust, that is, the higher degree of social fairness is connected with the higher degree of social trust.

Social security, social fairness and SWB
At present, social fairness is an important theme of social governance in China. It is a necessary link in improving social security to promote social fairness. Related research showed that residents' general perception of fairness is slightly lower than the socially recognized trust level. In other words, people are still troubled by a lack of fairness in life satisfaction (Gao & Qin, 2018). From the perspective of social fairness and justice, we can fully understand the impact of social factors on human psychology and behaviors (Schneider, 2015). Social unfairness will stimulate people to appear in a series of resistive behaviors seeking justice and negative psychology. Studies have shown that as a part of social fairness and justice, income inequality will reduce the individual's level of perceived fairness and happiness (Ngamaba et al., 2018;Oishi et al., 2011;You, 2012). For example, Huang (2019) found that social fairness, especially equity in the distribution of income, is of great significance for the subjective happiness of individuals. Unfair social distribution and income inequality pose major threats to the personal interests, social progress and political stability, which greatly detracts from people's happiness and satisfaction. In addition, a South Korean study using data collected by Gallup Korea showed that social fairness can ignite people's hope for future development and reduce the risk of depression, which is beneficial for their SWB (Roh, 2021). The empirical data derived from 169,038 individuals nested within 28 EU countries also confirmed that social justice is highly related to life satisfaction. When people live in a fair environment, they can get the resources and assistance they deserve to withstand the risks and harms caused by the gap between the rich and the poor and the class stratification (Di Martino & Prilleltensky, 2020).
Social security plays a supporter role in safeguarding fairness. In particular, the assistance for disadvantaged groups demonstrates social fairness and justice, which is beneficial to the improvement of the entire SWB. Studies have shown, for example, that social assistance and security policies have a significant impact on the life satisfaction of disaster-affected people. If they get adequate social security, they will have a higher fairness perception of government relief policy resulting in life satisfaction of  (Liang & Cao, 2015;Wang & Li, 2020). As Amartya Sen said, the root cause of poverty and social inequality is the deprivation of viability, that is, the uneven distribution of rights and benefits (Sen, 1993;Sen, 1999). When people achieve a satisfactory distribution result, they perceive society to be fair. Indeed, the essence of social security is to achieve fairness through redistribution. The applicability and accessibility of social security are key to upholding social fairness and justice. Thus, it is inferred that social security has a positive effect on the realization of social fairness and justice, thereby enhancing people's wellbeing. However, studies on the mediating role of social fairness in the relationship between social security and SWB is still relatively scarce. Based on this, we put forward Hypothesis 3. Social justice plays a mediating role in the path between social security and people's SWB.

Social security, social trust and SWB
Social trust is the basis for interpersonal interaction and the interaction between citizens and the government (Amati et al., 2018;Zanin, 2016). The study using cross-national data of 39,082 participants from 29 Asian countries found that high social trust only accounted for 37%, while, low social trust was as high as 54%. People in the Maldives were at the greatest level of trust followed by China, and people in Cambodia reported the lowest level of trust (Tokuda et al., 2017). In terms of societal theories, social trust will be affected by social environmental factors, it is generated in a fairer social environment, including a reasonable distribution of resources and opportunities. Social trust is also an indicator that reflects the situation of social development (Delhey & Newton, 2003;Rothstein & Uslaner,2005). It contributes to economic growth and efficiency, the provision of public goods, to social integration, cooperation, and harmony, democratic stability and development, personal life satisfaction, and even good health and longevity (Appau et al., 2019;Herreros & Criado, 2008;Helliwell et al., 2016;Lu et al., 2018).
Empirical researches have shown that social trust is significantly related to people's SWB. For example, some scholars also discussed the impact of social trust on people's life satisfaction and wellbeing from the perspective of social capital, they believed that as an important component of social capital, social trust is closely related to SWB, and a high degree of social trust can improve people's SWB level (Appau et al., 2019;Clark & Lisowski, 2018;Piumatti et al., 2018;Portela et al., 2013).
Furthermore, Abbott and scholars (2015) confirmed that social trust has an impact on life satisfaction in the social quality model. The results explained why economic prosperity is not the only indicator of improvement in life satisfaction, but rather many social factors must be considered, such as social trust, social inequality, social solidarity, and social empowerment. Generally, the quality of social development such as policy and management problems (e.g., corruption) will not only reduce interpersonal trust, but also reduce citizens' trust in government institutions (You, 2012). A high level of social trust benefits to strengthen market vitality and social safety, improve interpersonal relationships and people's resilience, which plays a positive role in promoting people's mental health and SWB (Amati et al., 2018;Churchill & Mishra, 2017;Mikucka et al., 2017;Helliwell et al., 2016;You, 2012). Suriyanrattakorn and Chang (2021) found, using a cross-country panel data set for 97 countries in the period 2011-2019, not only that the positive direct relationship between trust in government and life satisfaction, but also found that trust in government policies and services can attract more capital into the market to stimulate economic prosperity, which indirectly has a positive effect on SWB. While, lack of social trust will contribute to conflict and contradiction, economic recession, and poor wellbeing (Suriyanrattakorn & Chang, 2021). It speculates that good social security policies can strengthen individual social trust and thereby promote SWB (Kapteyn & Zamarro, 2013;Wang & Li, 2020). There is still insufficient research on social security, social trust and SWB in China.
Social trust is placed in an intermediary position, whether more significant results can be achieved. For this reason, the study proposes Hypothesis 4. Social trust plays a mediating role in the relationship between social security and people's SWB.
As far as we know, scholars have conducted a variety of empirical studies on SWB, social justice and social trust from different angles, and laid a theoretical foundation for academic development and policy improvement. However, there are still some shortcomings in research on social security and SWB. Most studies explored the impact of social security on SWB from a single dimension rather than as a whole, or analyzed the direct relationship between them. But there is insufficient research into whether social security can have indirect or even multiple indirect effects on SWB through certain factors. In order to fill the literature gaps especially in China, this study takes two intermediary variables into consideration, including social justice and social trust, to construct a chain mediation   1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64  65 model. We propose Hypothesis 5. Social justice and social trust play a chain-mediating role in the relationship between social security and people's SWB. That is, higher quality of social security can improve social fairness, thereby increasing social trust, and ultimately promoting people's SWB. The conceptual framework is shown in Figure 1.

Dependent variable
SWB is viewed as the dependent variable in this research, which is reflected in happiness or life satisfaction (Diener, 2009;Diener & Diener,1995;Pavot & Diener, 2008). Self-rated satisfaction with life and income has been used in the measures of SWB (Ng et al., 2017). Hence, it is measured by the following in 2017CSS. "Please use 1-10 points to express your assessment of satisfaction, including family financial status, the environmental situation of residence, and your overall satisfaction with life." The values range from 1 (very dissatisfaction) to 10 (very satisfaction). Higher mean scores are associated with higher levels of SWB.

Independent variable
In this study, social security is the independent variable. It refers to the maintenance of social functions through government and the protection of people's lives. It is measured by question E1c with six items. (Please use 1-10 points to express your evaluation of the current social security situation, including pension security, medical security, employment security, urban and rural minimum living security (Dibao), basic housing security such as affordable housing, public rental housing, and low-rent housing, and in general, the social security status.). From 1 to 10 respectively are very dissatisfied to very satisfied. Higher averages indicate a higher quality of social security.  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64  65 strangers.), and institutional trust (Do you trust the following agencies? Include central government, district/county Government, township government). Options from one to four respectively indicate very distrust to very trust. And higher average values mean a higher degree of social trust.
Hayes (Hayes, 2017)  however, even if  2 is significant, models with higher satisfaction with other values can be accepted (Bentler, 1990;Bollen, 1989;Browne & Cudeck, 1992). AVE (average variance extracted) is over 0.4 and CR (construct reliability) is over 0.8 except for the social trust factor closing 0.7 in the study. And standardized loading factor values are above 0.5, which can be accepted (Agnew, 1991). Therefore, the measurement model is satisfactory, and structural model analysis can be carried out. Details are given in Table 1.

Descriptive results and correlations
The distribution of demographic characteristics in the descriptive result is relatively balanced. Descriptive statistics and correlation analysis of variables in the study can be found in Table 3.

Fig. 2a
Regression variable graph between social security and SWB colored by gender.

Fig. 2b
Regression variable graph between social fairness and SWB colored by gender.

Fig. 2e
Regression variable graph between social trust and social security colored by gender. Figure. 2f Regression variable graph between social trust and social fairness colored by gender.
The results show that the total effect of SWB explained is 49% in the chain mediation model. The direct effect of social security on SWB is 43.4%, accounting for 88.6% of the total effect, and the   1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64 indirect effect is 11.4% of the total effect. Specifically, the indirect effect of the model mediated by social fairness accounts for 56.6% of the indirect effect, which is the most influential path. The path effect mediated by social trust accounted for 25.9% of the indirect effect. The model effect with social fairness and social trust as the chain intermediary accounted for 17.3% of the indirect effect. The bootstrap CI (95%) in all paths does not contain zero, indicating that the effect is significant. Thus, the results support the above-mentioned research hypotheses, and the full information is presented in Figure 3 and Table 5.  BootSE is bootstrap standard errors. BootLLCI is bootstrap lower bound of the confidence interval.
BootULCI is bootstrap upper bound of the confidence interval. RE is the relative effect.

Discussion and conclusion
In summary, this study used data from 2017CSS to test the chain mediation model. We examined the  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64  65 relationship among social security, social fairness, social trust, and people's SWB. And the results support our hypotheses above. The chain mediation effect exists in the relationship between social fairness and social trust. High levels of social security predicate good conditions of social fairness, stimulating the degree of social trust. Finally, people's SWB is able to be influenced by this virtuous circle. Because of this, we also put forward several policy suggestions to improve the people's SWB.
Details discussed are as follows.
First of all, social security is a positive predictor of people's SWB, which is consistent with existing studies. (Abruquah et al., 2019;Altun & Yazici, 2015;Tran et al., 2016). Under the Chinese governance model, people are highly dependent on the government, and they are eager to get more policy supports so as to be free from life pressure. Therefore, policy security plays a prominent role in maintaining social stability, promoting economic prosperity, and improving people's livelihoods. As a public service, the field and scope of social security coverage will directly affect people's life quality.
Especially for vulnerable groups in society, social security, such as education, medical care, employment, pensions, and social assistance, is the final barrier for them to receive support. Social security ensures a more balanced distribution of national interests and narrows the gap between the rich and the poor. Under the premise of satisfying people's basic lives, high-level social security can further improve life quality (Abbott et al., 2015;Abbott & Wallace, 2014;Sun & Xiao, 2011). This may be the reason for the findings. Secondly, the results show that social trust can be positively predicted by social fairness, which supports the relevant literature (Brugman et al., 2016;Zmerli & Castillo, 2015;Zhang & Zhou, 2018). It also proves the applicability of fairness heuristic theory in Chinese context. Positive human behaviors are more likely to be inspired in the fair surrounding, such as trust and trustworthiness (Lind, 2001;Jones & Martens, 2009). The result is likely to be explained by this.
Because the sense of fairness will let people put down their guard and treat others equally, it declines prejudice, discrimination, and conflict in society. This contributes to forming a harmonious society and enhancing interpersonal trust and organizational trust.
Our results also show that social fairness plays partly a mediating role between social security and people's SWB. The rapid development of China's economy has also brought about the gap between the rich and the poor and the duality of urban and rural areas. Inequality cannot be completely eliminated by relying on individual strength. Hence, the government needs to play a Macro-control role for fairness and justice. A tool of government regulation is the social security system, that is, social   1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64 security improves social fairness as a whole by making up for the unfairness at the start and end. Therefore, people's sense of acquisition and satisfaction with social security greatly affects their evaluation of social fairness, and also affects their perception of belonging and identification with society. A solid social security system and social welfare are valuable in maintaining the stability of people's lives and promoting social fairness. It is able to inspire their confidence in life benefiting SWB, which is consistent with the recent research (Di Martino & Prilleltensky, 2020;Huang, 2019). At the same time, we also confirmed the partial mediation role of social trust in the relationship between social security and SWB. As societal theory believes, the breeding of social trust requires a good social environment, and safety and survival are the keys. The government helps citizens overcome life risks and difficulties by providing them with all the guarantees they need in life, which is conducive to improving their sense of security and survivability. This will not only increase people's trust in government but also increase interpersonal trust, which can build a positive social network system promoting overall social trust. The high degree of social trust is beneficial to improve social quality in the social quality model, and people's SWB level can also be enhanced indirectly or directly in this way.
Based on this, we verify the existence of chain intermediary through the chain mediation model test.
According to social systems theory (Luhmann, 1984), the elements and links of different systems in society are interconnected. When an error occurs in a subsystem, other aspects are negatively affected.
On the contrary, the improvement of one system function will also lead to the optimization of other functions. The coordinated operation of the social system can create a stable social environment that is of positive significance to people's lives. As an important part of the social governance system, the quality of social security will have a series of social impacts. High-quality social security can promote social fairness, thereby strengthening social trust, forming benign chain effects, and then increasing people's SWB. It is a possible reason why the chain model is supported.
In addition, the data also show that age and education level in the control variables are significantly related to SWB. Age negatively predicts people's SWB level, that is, people's SWB will decline with aging, which supports previous research (Vera-Villarroel et al. 2012). In terms of the Ushaped relationship between age and wellbeing (Blanchflower & Oswald, 2008;Weiss et al., 2012;Schwandt, 2016), people's expectations for life will increase as people grow older, and they will lower their expectations until they enter the old stage, and the reality gap will also change from large to small ,   1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64  65 creating a trend that their life satisfaction first decreases and then increases. In addition to facing many life pressures such as unemployment, divorce, daily expenses, etc., middle-aged people in China have gone through the process of social transformation that has a huge impact on their lives, thus, their life satisfaction will be minimized (Sun & Xiao, 2011). The age distribution of this research group is concentrated in the middle-aged stage. It is in the first half of the U-shaped relationship transition, so this result can be accepted. However, the relationship between educational level and SWB fails to support some studies (Kristoffersen, 2018;Sun & Xiao, 2011). Their research showed that there is no obvious relation or negative relationship between educational level and SWB. Because well-educated people place higher requirements on life circumstances, this may allow them to meet expectations at the expense of leisure time and overloaded work, thereby reducing SWB. While, our results support a significant positive correlation between education level and people's SWB (Cuñado & De Gracia, 2012;Jongbloed, 2018), namely, well-educated people have a high level of SWB. This may because of different research backgrounds. In contemporary Chinese society, educational attainment is closely related to personal achievements, employment opportunities, income, and welfare benefits. Compared to people with a low level of education, people with a high level of education are more likely to obtain opportunities and social status, high economic incomes and high welfare benefits, all of which are conducive to improving an individual's SWB (Michalos, 2017;Ruiu & Ruiu, 2019).

Contribution and limitation
In line with the aforementioned content, it is worth noting theoretical and practical contributions in our study. At the theoretical level, our empirical results show that good quality of social security can produce positive outcomes including fairness and justice, trust, and SWB. It also proves the suitability of some theories in the Chinese context and contributes to enriching academic results. The chained mediation model can also provide a reference for follow-up related research, we should view and address social problems from an interconnected rather than separated perspective in order to avoid falling into a vicious circle. From the practical aspect, we provide targeted policy recommendations for improving people's SWB. Firstly, the state should ensure fairness and justice as far as possible in establishing and improving the social security system. It is necessary to warrant that the interests of high-income groups are not violated and that low-income groups can receive relative support, while the actual claims of middle-income groups are also taken into account. Continuously expand the field of social security and improve the level of social security, and this will increase the accessibility and satisfaction of all citizens to social welfare, and lay the foundation for improving social fairness.
Secondly, government management and democratic participation should be fully integrated into social governance to pledge the policy applicability, social order and safety, and improve the level of social trust (Keping, 2017). Finally, Chinese government needs to establish a perfect supervision and feedback mechanism to ensure the implementation of social security policy. And public opinions and suggestions need to be heard so as to improve public services and social security and enhance people's well-being achieving the ultimate goal of social governance.