Introduction
The goals of stress and care burden on elderly caregivers can affect the psycho-social conditions of the elderly in various ways and make the nursing home an unpleasant experience for the elderly. This issue can cause stress levels for the elderly and their caregivers [1]. The concept of resilience means the ability of people to effectively face stressful situations and turn them into opportunities. Resilience is a personality trait that moderates the adverse effects of stress [2, 3]. Due to the necessity of examining the role of resilience in the relationship between perceived stress and caregiving burden and its particular importance in reducing the harmful effects of stress and caregiving burden, this research was conducted among the caregivers of the elderly in nursing homes in Tehran in 2015.
Methods
This cross-sectional and correlational research was conducted with a survey method. The statistical population of the present study was all the official caregivers of the elderly in the 24-hour elderly centers in Tehran (19 centers) in 2017 (one-year time frame) who were included in the study as a whole. Finally, 142 people were included in the study as a sample group. The participants of this study included caregivers who had been working in elderly centers for at least 3 months and who performed care work at least 3 days a week and 3 hours each time in their work shifts. In addition to the logical reasons, these time criteria and the caregivers’ history are given according to the requirements mentioned in some related texts and Amanian’s thesis (2012)-quoted from Cheng. 
The participants of the current study signed informed consent. Demographic questionnaires, Cohen et al.’s perceived stress (1983), the short form of Zarit et al.’s (1986) care burden questionnaire, and Conner and Davidson’s resilience (2003) were used to collect information. Before completing the questionnaire, a brief explanation about the study was given to the participants. Also, during the questionnaire completion, the researcher answered the participants’ questions regarding the questionnaire and its expressions. 
After the preliminary study of the theories and determining the reliability and validity of the questionnaires, the research was carried out in Tehran. Visiting the centers caring for the elderly in Tehran City, the caregivers of the elderly completed questionnaires on demographic characteristics, perceived stress, care burden, and resilience. After collecting the questionnaires and entering them in SPSS software v. 20, the results were analyzed. Descriptive statistics techniques, such as frequency tables, mean calculation, and standard deviation (SD) and inferential statistics, such as Pearson’s correlation, were used to analyze research data.
Results
The participants of this study included 142 people (92 women, 50 men) from the official caregivers of nursing homes for the elderly in Tehran (22 to 53 years old, with an average age of 35.38). In terms of marital status in 3 groups single (27%), married (40.1%), and divorced (32.4%), in terms of education in two groups of university education (22.5%) and non-university education (77.5%), in terms of work experience of the participants They had a minimum of 3 months of experience and a maximum of 13 years. 
The participants were divided into two groups with income below one million tomans (35 people) and above one million tomans (107 people). The results of the research data analysis indicated that the members of the sample group endure high stress. Among the demographic variables, the participants’ perceived stress score had a significant relationship with the variables of education and marital status. Also, the target group had a significant association with education and marital status regarding the care burden variable, with an average score of 22.60. According to the obtained average values, it was found that the subjects’ resilience was in the middle level (number 50), and the caregivers of the elderly reported moderate resilience.
To investigate the moderating effect of the resilience variable in the relationship between perceived stress and caregiving burden, three regression models have been used:
In the first model with an acceptable fit (P<0.001, f=274.6), it was found that there is a positive and significant relationship between perceived stress and care burden (β=0.814), and about 66.2% of Changes in caregiving burden were explained by perceived stress.
In the second model with an acceptable fit (P<0.001, f=144.14), it was found that there is a positive and significant relationship between perceived stress and care burden (β=0.714) and a negative relationship between resilience and care burden, which is significant (β=-0.150). Also, about 67.5% of care burden changes were explained by two predictor variables entered into the model.
In the third model, according to the results, there was a positive and significant relationship between perceived stress and care burden (β=0.773) and a negative and significant relationship between resilience and care burden (β=0.110). . Also, the interactive effect of perceived stress and resilience on care burden was negative and significant. Based on the coefficient of determination, about 73% of the care burden changes were explained by the two predictor variables entered into the model and their interactive effect. The implemented regression model had an acceptable fit (P=124.33, H<0.001).
Discussion
The results of this study indicated the moderating role of resilience in the relationship between perceived stress and care burden in elderly caregivers. Therefore, according to the results, it is recommended that all governmental and non-governmental institutions providing services to the geriatrics and the elderly and health policymakers offer comprehensive services to increase the quality of services, reduce injuries caused by stress and burden of care in elderly caregivers are part of the services, and to focus on improving resilience and paying attention to internal resources of the elderly. Also, considering the importance of the concept of resilience, it is recommended to conduct interventional studies to investigate the impact of interventions in resilience on the quality of caregivers’ services, as well as the effects of these interventions on the level of anxiety, stress and care burden reported by this group. It is also suggested to pay attention to other internal and external factors that can mediate and moderate the care process in future studies.

Ethical Considerations
Compliance with ethical guidelines
The ethical considerations of the present study included the informed consent of the participants to participate in the research and the possibility of their free exit from it, confidentiality and protection of their personal information. Also, the current research was approved by the ethics committee of University of Social Welfare & Rehabilitation Sciences.

Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors' contributions
Conceptualization: Mehsa Jafari, Fardin Alipour and Ghanche Raheb; Data collection and analysis: Mehsa Jafari; Writing of the first version: Mehsa Jafari, Fardin Alipour and Mostafa Mardani; Editing and finalization written by: Mostafa Mar

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
The authors are grateful to all involved, the data collection group and all participants in the research.


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