**1. Introduction**

According to the seventh national census of China, the number of people aged 60 and above in 2020 was 260 million accounting for 18.7% of the total population, and the number of people aged 65 and above was 190 million accounting for 13.5% of the total population [1]. Although China is still in the mild aging stage, it is about to enter a moderate aging society. The scale and proportion of the elderly population will continue to expand. The increasingly serious problem of the aging population not only brings great pressure to the country but also poses various threats to the health and security of the elderly.

With the increase of age, the physiological health of the elderly population is declining, and the mental health issue has become more prominent in recent years. The physical and mental health problems of the elderly bring a series of challenges to the construction of China's public health system, the construction of an age-friendly society, and the formulation of health standards for the elderly. In particular, China still has a typical dual economic structure at present. The health levels of the elderly population in urban and rural areas differ greatly, and they also face different health risks. At the same time, the socioeconomic status of the elderly begins to decline after a significant shift in their social roles, which often affects their overall living status, leisure and recreation status, health-care status, etc. Quality of life has an intuitive impact on the health status of the elderly. Leisure and recreational activities not only relieve the stress and tension in life, but also help to enhance social interaction among the elderly, maintain the stability of human body functions, and improve the psychological state. Health-care services, as a means of protection when health is at risk, play a last resort role in the health of the elderly.

**Citation:** Zhou, W.; Hou, J.; Sun, M.; Wang, C. The Impact of Family Socioeconomic Status on Elderly Health in China: Based on the Frailty Index. *Int. J. Environ. Res. Public Health* **2022**, *19*, 968. https://doi.org/ 10.3390/ijerph19020968

Academic Editors: Roberto Alonso González Lezcano, Francesco Nocera and Rosa Giuseppina Caponetto

Received: 8 December 2021 Accepted: 13 January 2022 Published: 15 January 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

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The Outline of Healthy China 2030 Plan proposed to promote healthy aging and ensure the health of the elderly [2]. The fifth plenary session of the 19th CPC Central Committee approved the CPC Central Committee's Proposals on Formulating the 14th Five-Year Plan for National Economic and Social Development and the Long-Term Goals of 2035, which proposed to comprehensively promote the construction of a healthy China, give priority to the development of the people's health, implement the national strategy of actively responding to population aging, and actively develop human resources for the elderly [3]. The implementation of active aging and the development of human resources for the elderly can delay the decline of their socioeconomic status and promote active aging and healthy aging.

In a marriage-based family, the husband and wife are closely interdependent in life and economy. They support each other and share their weal and woe. Both parties determine the socioeconomic status of the entire family, which in turn has a very important impact on both parties. However, existing studies (reviewed in Section 2) have mostly analyzed the effects of older adults' socioeconomic status on their self-rated health, physical health, and mental health but less on their overall health status from the perspective of family socioeconomic status. Based on the above research backgrounds, it is of great theoretical and practical significance to analyze the impact, heterogeneity, and different mechanisms of the family socioeconomic status of the elderly on their comprehensive health status. Theoretically, it makes up for the shortage of research between family socioeconomic status and elderly health from a comprehensive perspective. Realistically, it calls for more attention to help the elderly improve their family socioeconomic status and comprehensive health status from different dimensions and reduce the inequalities within them, and provides a reference basis for the formulation of public health policy for the elderly, so that they can enjoy happy and healthy lives and successfully achieve healthy and active aging.

### **2. Literature Review**

The health production theory suggests that people's optimal decisions about their health needs are influenced by a variety of factors, including health insurance, lifestyle, education, income status, and living environment [4]. The health causation theory holds that health is also influenced by social structural factors, and socioeconomic status of an individual affects their health status. The higher the socioeconomic status, the better the health status [5]. The social stratification theory assumes that the differences between social groups are universal. People have both natural and social differences. Natural differences are formed by the physical differences of people, whereas social differences are formed by people due to social factors, such as political, economic, cultural, and interaction relationships. It is based on certain criteria for distinguishing people's positions in social activities and social relations, and the common stratification criteria are economic income, occupation, education level, power, etc. [6]. The existence of social stratification structure leads to the inequality of socioeconomic status and family socioeconomic status.

Socioeconomic status based on the social stratification theory is the social class or position in which an individual or group is located and is a comprehensive reflection of education level, occupational rank, income level, etc. Inequality in socioeconomic status can lead to inequality in one's own health. Several scholars have revealed this phenomenon through their studies. Winkleby found that socioeconomic status plays a determinant role in almost all diseases and all stages of life [7]. He found that the household income of older adults has a positive effect on their life satisfaction and physical health status and occupational status only has a positive effect on their physical health status, but education has no effect on their life satisfaction and physical health status [8]. Zhang et al. concluded that elderly people with low socioeconomic status, poor income level, low education level, and manual labor-oriented jobs or no job mostly have severely underutilized health services or no health-care coverage at all, leading to the worsening of their own health status [9]. Kuo et al. examined the impact of socioeconomic status on colorectal cancer risk, staging, and survival under the National Health Insurance system in Taiwan [10]. However, these studies mainly analyze the different dimensions of socioeconomic status and lack a comprehensive consideration of socioeconomic status. Some scholars use the socioeconomic status index to study its impact and mechanism on the health of the elderly. Cristine et al. suggested that people with lower socioeconomic status are more likely to be in an unfavorable environment and have negative emotions and potential stress, which in turn have a negative impact on their health [11]. Xue et al. suggested that socioeconomic status affects the physical and mental health of older adults through mediating variables, such as sleep quality, dietary patterns, physical activities, and social participation [12]. Liu et al. found that socioeconomic status positively influences the health of older adults through food access, physical activities, recreational activities, and improving their overall well-being [13]. Wang et al. extended the study of the influence mechanism from a social capital perspective and found that high socioeconomic status groups increase their health advantage through a high frequency of social interactions with friends; low socioeconomic status groups mitigate the health disadvantage caused by low status through social trust [14]. However, these studies do not consider the impact of socioeconomic status from a family perspective.

Family socioeconomic status is a comprehensive reflection of the individual socioeconomic status of family members, and it is the social class or status of family members based on the family cooperation model. Unequal family socioeconomic status can negatively affect education, occupational status, and the health of children. Javier found that the lower the family socioeconomic status of elementary school students, the lower their scores in basic competencies [15]. Meng et al. investigated the family socioeconomic status in China and found that the socioeconomic status of students' families has important effects and constraints on the students' preferences with regard to the different types of higher education schools and majors [6]. Zhu et al. argued that the influence of family status on the youth's attainment of initial position is changing in a wave-like fashion [16]. Cheng et al. found that the family socioeconomic status of secondary school students is significantly and positively related to overall psychological quality and its dimensions [17]. Unequal family socioeconomic status can also lead to inequality in individual's health. However, only a few studies have focused on this aspect. Huang et al. concluded that a higher family socioeconomic status has a significant contribution to their own health in China [18]. Cao et al. thought consistently higher early family socioeconomic status and upward socioeconomic status mobility will lead to a higher incidence of good health in old age, while continuous lower early family socioeconomic status is the opposite, that is, the impact of early family environment on the elderly health is cumulative [19]. Ghasemi et al. found that subjective perception of family socioeconomic status can explain differences in health-related quality of life of low-income people in Iran [20]. Booysen et al. also found that family structure and family socioeconomic status both have an influence on public health [21]. However, these studies do not clarify how family socioeconomic status affects the comprehensive health status of the elderly.

Based on the above literature analyses, we think that many studies have been conducted on both socioeconomic status and family socioeconomic status, but the existing studies mainly focus on the influence of individual socioeconomic status on the health status in different dimensions of themselves, more on the intergenerational influence of family socioeconomic status on children and less on the impact and mechanism of family socioeconomic status on comprehensive health status. We know that when the socioeconomic status of a family is higher in real life, its members usually enjoy better living conditions, abundant leisure and entertainment activities, and high-quality medical and health services, which will have a positive effect on their health. Therefore, based on the above theories, this study creatively analyzes the impact and mechanism of family socioeconomic status on frailty index. In the present study, the total family income, the comprehensive years of education, and the comprehensive occupational rank before retirement of elderly couples were synthesized into the family socioeconomic status index. The frailty index was used as a measure of the comprehensive health status of the elderly. The impact of family

socioeconomic status on elderly health was first analyzed, followed by the differences in the impact of family socioeconomic status on the health status of different elderly groups as well as the possible mechanisms of the impact. Figure 1 shows the specific theoretical analysis framework.

**Figure 1.** Framework diagram of theoretical analysis.

#### **3. Study Design**

#### *3.1. Data*

The data used in this study were obtained from the Chinese Longitudinal Healthy Longevity Survey in 2018 (CLHLS was downloaded from https://opendata.pku.edu.cn/ dataverse/pku (accessed on 1 November 2021)), which is a national-wide and longitudinal survey of the elderly organized by the Center for Healthy Aging and Development Research/National Development Research Institute of Peking University. The detailed information about the survey design has been reported in previous research [22–24]. The samples were collected from 23 provinces of China, and the total number of valid samples was 15,874. The contents of the surviving respondents' questionnaires included the basic conditions, socioeconomic conditions, and various health conditions of the elderly, which cover all aspects of the elderly and meet the needs of the study. In the present study, elderly people aged 60 and above were included, and 7599 samples were obtained after deleting those samples with missing or invalid variable values.

#### *3.2. Variable Descriptions*

#### 3.2.1. Explained Variable

The explained variable is the comprehensive health status of the elderly, and the frailty index is used as a measurement method. The frailty index, or cumulative health deficit index, refers to the proportion of health deficit indicators among all measures of health for an individual and can be understood as an accumulation of health deficits. Health deficits can be measured somatically, functionally, and psychologically [25]. The number of variables used to construct the index is not standardized, usually ranging from 30 to 70 and taking values between 0 and 1 [26]. Drawing on previous research results and combining data availability and research objectives, this study selected 32 indicators measuring health status to construct the frailty index, covering self-rated health status (SHS), activities of daily living (ADL), instrumental activities of daily living (IADL), the center for epidemiological studies–depression (CES-D), and the self-rated anxiety scale (SAS). The SHS was assigned in the following manner: 0, "very good"; 0.25, "good"; 0.5, "general"; 0.75, "bad"; and 1, "very bad". The ADL are reflected by the elderly's problems in bathing, dressing, toileting, indoor transferring, control of urination and defecation, and feeding (six aspects). For each aspect, if the elderly does not need assistance, a value of 0 was assigned; if the elderly needs one part assistance, a value of 0.5 was assigned; and if the elderly needs more than one part assistance, a value of 1 was assigned. The IADL are reflected by the questions of whether the elderly can go outside to visit neighbors, go shopping, make food, wash clothes, walk 1 km continuously, carry a 5 kg weight, crouch and stand three times continuously, and

take public transportation by themselves (eight aspects). For each aspect, if the elderly can do so, a value of 0 was assigned; if the elderly encounters little difficulty, a value of 0.5 was assigned; if the elderly is unable to do so, a value of 1 was assigned. The CES-D consists of 10 questions, with regard to whether the older person is bothered by some small things, has difficulty in concentrating, feels sad or depressed, struggles to do things, has hope for the future, feels nervous or afraid, is as happy as when he or she was young, feels lonely, and feels unable to continue life as well as his or her sleep quality. For the seven questions reflecting negative emotions, the assigned values were as follows: 0, "never"; 0.25, "seldom"; 0.5, "sometimes"; 0.75, "often"; and 1, "always". For the three questions reflecting positive emotions with regard to whether the elderly has hope for the future and is as happy as when he or she was young as well as his or her sleep quality, they were assigned with the opposite values. The SAS is composed of seven questions with regard to whether the elderly feels uneasy, worried and annoyed, cannot stop or control worry, is worried too much about all kinds of things, is very nervous and finds it difficult to relax, is so anxious that he or she cannot sit still, easily gets annoyed or irritated, and feels as if something terrible is going to happen. We assigned the values according to the frequency of each problem: 0, "never"; 0.33, "for several days"; 0.67, "more than half of days"; and 1, "almost every day". Finally, the scores of the 32 indicators were summed and then divided by the theoretical maximum score of 32 to obtain the frailty index of each elderly person.

#### 3.2.2. Explanatory Variable

The explanatory variable is the family socioeconomic status of the elderly, which consists of three dimensions: total family income, comprehensive years of education, and comprehensive occupational rank before retirement of the elderly couple (for the currently spouseless elderly, this study used their own years of education and occupational rank before retirement). The total family income is the total income of the whole family in the last year, which was processed logarithmically in this study. The range of years of education is 0–22 years, and those samples with 22 years or more of education were treated as 22 years. For the occupational level before retirement, in accordance with the study of Xue and Ge, the present study defined "professional, technical, governmental, institutional, managerial, and military personnel" as senior practitioners assigned with a value of 3; "commercial, service, and industrial workers" as intermediate practitioners with a value of 2; and the other options as general practitioners with a value of 1 [12]. For the years of education and occupational rank, previous studies have only considered the elderly individuals. Therefore, in the present study, the spouses of the elderly were also taken into consideration. We calculated the comprehensive years of education and occupational rank before retirement of the elderly couples in accordance with Zhu and Li's study, which enables to evaluate the advantages and disadvantages of the different types of family status more accurately using an approach based on the Pythagorean theorem [16,27]. Finally, the present study used the entropy weight method to synthesize the total family income, the comprehensive years of education, and the comprehensive occupational rank before retirement of elderly couples into a family socioeconomic status index. The entropy weight method is currently the main method of objective assignment method, which aims to assign weights to each evaluation index based on the degree of difference between its values and construct a composite index.
