Life satisfaction analysis of occupational balance group: based on Korean time use survey data (KOSTAT) of older adults

Background: The purpose of this study was to identify whether there is a difference in time use between a group of subjects with occupational balance, the occupational balance group (OB group) and a group of subjects lacking occupational balance, the occupational imbalance group (OI group), and what factors inuence the life satisfaction of the OB group. This study used raw data from the 2014 Time Use Survey of the Korea National Statistical Oce (KOSTAT). Methods: This study sorted detailed activities of the 9.228 subjects who were over 65 years of age. We conducted an independent sample t-test to conrm the time difference by areas between the OB group and the OI groups. In order to conrm the effect of variables on life satisfaction, we performed regression analysis by applying an ordered probit model (OPM). Results: The analysis of time use corresponding to eight activity areas showed the greatest time use for the instrumental activities of daily living (IADL), followed by rest and sleep, leisure, and activities of daily living (ADL). The largest effect size (ES) was social participation, followed by leisure, IADL, and work. As a result of analyzing the factors affecting the life satisfaction of the OB group, we found that lower age, females, a higher level of education, a lower need for care, higher income, and agricultural residence tended to correspond to higher life satisfaction. Conclusions : This study may provide a basis for the development of the time ‐ use management and lifestyle redesign programs to assist older adults in pursuing disease prevention and health maintenance roles by themselves.

According to the Survey of Household Finance and Welfare (2017) by the Korea National Statistical O ce (KOSTAT), the average retirement age of householders in Korea is 62.1 years old, which means they have to live for more than 20 years without regular income after retirement [7]. In 2016, only 7.1% of the Korean population were pension recipients, but this re ects a steady increase from 3.0% in 2013 and 4.38% in 2014. This indicates retirees have been recognizing the importance of regular cash ow by gradation [8]. Unlike other countries, in Korea, National Health Service (NHS) spending occupies a strictly high proportion of the public medical security system.
The medical expenditure of older adults for health insurance rose very rapidly from 2010 to 2016, in proportion to the growing population of the aged. In 2016, there were 6.45 million people aged 65 or over that received national health care bene ts, accounting for 12.7% of the whole population. The medical expenditure was 25 trillion 18.7 billion KRW, accounting for 58.7% of their entire expenditure. The monthly average medical expenditure per capita among those aged 65 or over was 3.1 times greater than the monthly average medical expenditure of the whole population [9]. Therefore, it is possible to provide evidence supporting the intervention of time use and for developing programs by ascertaining the patterns of time use by older Korean adults in their living after retirement and determining the correlation between this, health and life satisfaction.
Time use is employed to evaluate occupational balance (OB). OB refers to a status wherein labor, rest and the amounts of time for labor and rest are distributed at an appropriate ratio and occupational imbalance (OI) occurs when the excessive use of time in one area worsens health or the quality of life [10,11]. OB refers to a balanced participation by individuals in their daily occupational life [12]. In the study by Matuska and Christiansen, OB refers to a condition in which a person can live a healthy and meaningful life in a given day-to-day occupational life [13]. Maintaining a good balance of occupation means using living time in the activity areas that one needs in an appropriate distribution. OB perceived by an individual is likely to be in uenced by the amount of time spent in everyday occupation. Time-use is used to evaluate OB and occupational engagement [14]. If the OI is precipitated by a time imbalance, the level of health and life satisfaction will deteriorate. Therefore, the time use of the subjects should be grasped and should be included in any goal setting and intervention. The OI causes the imbalance of the remaining activity areas as a result of a one-sided occupational performance pattern, which can ultimately deteriorate the life satisfaction and health, lead to impairment or disease and hinder successful aging [15]. Therefore, understanding time use is necessary in assessing the OB, which shows how to choose mandatory and non-mandatory activities according to the value of an individual [14,16].
Effective time use shows good time management and outstanding self-management skills. These selfmanagement skills balance a person's needs and emotions and include proper management of temporal demands [17]. The study of 24 hours of living time can allow us to grasp the everyday life of an individual and the social structure around the individual. In particular, this temporal approach is suitable for dealing with the daily living of older adults, which is di cult to grasp by other o cial and economic approaches [18].
In the research comparing time use between older Korean adults and older foreign adults, older Korean adults spent the greatest number of hours in IADL among the seven activity areas other than rest and sleep. They spent the greatest portion of the day doing IADL, including housework and taking care of grandchildren and family members. This was followed by leisure and work. They primarily spent their leisure time using media and the majority of work was unpaid family affairs or volunteer work, not paid work.
Based on the results of American Time Use Surveys (ATUS), older adults in the US spent the greatest number of hours in leisure among the seven activity areas other than rest and sleep The older adults in the US spent time engaged in diverse sports activities like playing golf, walking and swimming and leisure activities, including using media [19]. This was followed by IADL activities such as housework and gardening, and social activities to connect with family members and friends. But they spent very little time on working, playing or learning [20].
Occupation is an activity that has a unique meaning and purpose in the life of an individual and is at the center of individual identity and competence, which in uences the individual in spending time and making decisions [6]. Occupation is important enough to be considered as a part of a life description, and experiencing meaningful occupation has a positive impact on health [21]. Occupation is very critical to human beings and occupation and time have an inseparable relationship with each other, since people are involved in occupations every hour [22]. Participation involves the balance of activities as well as diversity, meaning, and social factors of everyday use [23]. In order to determine the relationship between occupational engagement and health, occupational therapists have studied various concepts where OB is one of the important concepts. Experience of meaningful occupation has a positive impact on health and therefore, participating in a task successfully re ects the subjective value of an individual [24].
OB is very important to human beings and for older adults, maintaining OB adequately is directly connected to good health. This motivates humans to plan and manage their lives for quality. In particular, people who are not su ciently provided with an opportunity to work suffer damaged health and eventually they have a di culty surviving. This demonstrates that OI may cause damage to health or a disease by worsening qualitative aspects of health and life [3]. Countries, therefore, need to be more aggressive in providing environments for older adults to improve their life satisfaction by maintaining OB or in establishing and enforcing older adults health care policies by developing health programs considering the physical abilities of older adults or by cultivating specialists [25]. reported that they applied a lifestyle re-design program to older adults with dementia to improve their productivity as well as their life satisfaction [27]. There was a systematic review of time use that analyzed the amount of time use through a survey of the time spent by healthy elders, analyzing the changes in time use by age and by year according to the occupation of South Koreans and so on [28].
In early studies in Korea and abroad, those on the occupational balance analyzed how time use varies in labor, self-management, and leisure [29]. In many studies, the OB has been dealt with in the sense of personally perceived balance [14,30]. Bejerholm and Eklund analyzed that the time use of schizophrenic patients revealed a pattern that caused problems in their performance, and suggested that time management specialists should provide these clients with mediation to support their effective time use [31].
Activity theory explains that individuals accomplish successful aging when they maintain proper social activities. That is, life satisfaction is higher as older adults nd activities which can serve as substitutes for personal goals they had desired to attain in their occupation and life before reaching senility and as they are actively engrossed in such activities. This theory is made up of four pillars -social activity (the quantity of and the individual's interaction), social adequacy (the quality of an individual's social interaction as expressed in feelings of loneliness or its opposite), self-conception (the individual's image of his own worth as a person), life satisfaction (relative happiness with present circumstances in the context of one's lifetime experiences). It was supposed that the four pillars, making both direct and indirect in uence, form a causal chain in the order given [32].
Conversely, disengagement theory argues that social individuals are progressively separate from or drop out of the role system of middle age, as they enter old age and that this is a universal and indispensable process for the maintenance and sustainable development of the social system. Continuity theory remedies the weaknesses of the two con icting theories; activity theory and disengagement theory and says a good social activity in old age continuously performs a similar role, focusing on personal disposition and the role performed in middle age. This continuity theory is presented as a conceptual indicator of social activities for the aged [33].
Currently, it is necessary to provide supporting data to determine elders' health promotion and health care policy by verifying the OB through the living time of older adults. However, there are still few studies on the life satisfaction of older adults in the ROK after dividing the OB group and the OI group. For the OB group, all of eight activity areas are included in the scope of standard deviation, based on the mean value of life time. The OI group includes cases where even one of the areas is beyond the scope of standard deviation [27].
The purpose of this study was to identify whether there is a difference in time use by criteria (eight activity areas in total) and what factors in uence the life satisfaction of those in the OB group. To this end, we con rmed the use type of living time of older adults targeting healthy elders over 65 years of age in the ROK by classifying them into the OB group and the OI group. Based on the results of this study, we may identify the relationship among occupation, old age, health, and life satisfaction, and establish a retirement planning model for future generations of older adults' as well as older adults' households. We expect that this study will have important implications as a basis for intervention regarding time use and as basic material for program development.

Data and sample
According to the Korea National Statistical O ce (KOSTAT), the number of subjects in the 2014 Korean Time Use Survey (KTUS) was 26,988. This study sorted detailed activities of the 9.228 subjects who were over 65 years of age. The term healthy elders here refer to men or women aged 65 or more who are able to walk or drive independently, managing daily living on their own without epidemic or a serious chronic disease. This study used the raw data of 2014 KTUS of the KOSTAT, and classi ed the amount of time use of older adults into eight activity areas in total such as ADL, IADL, rest and sleep, education, work, play, leisure, and social participation [22] (Appendix 1).

Overview of the survey
We de ned the OB group as the cases where all eight activity areas fell within the standard deviation range based on the average value of living time. We identi ed the OI group as the cases where any item or items deviated from the standard deviation range. At this time, we analyzed the cases under 1 standard deviation (SD) from the mean or the cases over 1 SD from the mean [27].

Analysis method and main variables
We conducted independent sample t-tests to con rm the time difference by area (eight areas in total) between the OB group and the OI groups. We presented graphs to visually con rm the amount of living time. In order to con rm the effect of variables on life satisfaction, we performed regression analysis by applying an ordered probit model (OPM). In the survey, life satisfaction, which is a dependent variable of the time use is measured with an ordinal-type Likert scale. The OPM is a model that depends on the error of the standard normal distribution because it does not satisfy the basic assumption of the general linear regression equation. We used a statistical program SPSS 18.0 to analyze the frequency of general characteristics of the study subjects.

Results
The amount of time uses by activity areas For the amount of time use according to the occupational type of study subjects, we attained the following results. The greatest time use was IADL, which averaged 1513.59 minutes (56.34%), the average of rest and sleep was 532.82 minutes (19.83%), of leisure was 292.83 minutes (10.9%), and of ADL was 185.47 minutes (6.9%) in order. In this study, we classi ed the cases within 1 standard deviation as falling in the occupational balance group. IADL showed 1213.99 ~ 1813. 19  We represented the amount of living time by a graph in order to con rm it visually ( Figure 1 and Table 1).
Comparison of time use between the OB group and the OI group The time-use between the OB group (n=2,153) and the OI group (n=7,075) showed signi cant difference in ADL, IADL, rest and sleep, leisure, work, play, and social participation, but no signi cant difference in education (p = .001). Independent sample t-tests were conducted in order to con rm the difference in time by the eight activity areas according to occupational balance. A Welch-Aspin test was used instead of ttest if there was heteroskedasticity of the distribution of dependent variable as a result of the Levene-test. Compared to the OI group, the OB group used more time in ADL (t = 12.39, p = .001), IADL (t = 28.21, p = .001), rest and sleep (t = -25.65, p = .001), and leisure (t=27.99, p = .001) while it used less time in occupation (t=-25.65, p = .001), play (t = -5.85, p= .001) and social participation (t = -80.73, p = .001). The effect size (ES) is known as Cohen's d [34], and the ES increases as the difference between the two groups to be compared increases. Therefore, the activity areas with the largest time use difference between the two group were social participation (1.38), followed by leisure (0.66), IADL (0.59) and work (0.51) ( Figure 2 and Table 2).

Factors affecting the life satisfaction of the OB group
In order to con rm the factors affecting the life satisfaction of the OB Group, we conducted regression analysis applying an ordered probit model (OPM). The life satisfaction, which is a dependent variable of KTUS, has a 5-point scale selection-type category displaying from Very Unsatisfactory to Very Satisfactory, and the order among categories was meaningful. The static effect was signi cant in the case of age. The static effect was signi cant in males more than in the females (B = -0.12, p < .05), in middle school more than no educational attainment (B = 0.28, p < .01), high school than no educational attainment (B = 0.48, p < .001), college and university than no educational attainment (B = 0.65, p < .001), stroke than needs no help for ADL (B = -1.19, p < .01), disability than needs no help for ADL (B = -1.00, p < .001), other reasons than no needs help for ADL (B = -0.68, p < .001), less than KRW one million compared to over KRW three million (B = -0.43, p < .001), KRW one million compared to less than KRW two million, less than KRW two million compared to KRW three million (B = -0.32, p < .001), and lastly agricultural residence than non-agricultural residence (B = 0.29, p < .001). KRW is a combination of Korea's country code 'KR(Korea, Republic)' and the monetary unit 'Won' and is an abbreviation of 'Korean Won'. As a way of describing the spot exchange rate, the counter currency to the base currency is USD/KRW = 1,124 Won.
As a result of analysis, life satisfaction was higher in the case of middle school, high school, college or above than the cases of young age, female and no education. In the case of the reason for needing care, it turned out that the less need for care for stroke, disability, and other reasons, the higher the average annual household income (higher than KRW 3 million), and the more agricultural residence, the higher the life satisfaction (Table 3). Of the total 9,228 old people over 65 years old, those with work turned out to be 2,848 persons (30.9%), without work 6,380 (69.1%), full-time work 602 (6.5%) and part-time work 516 (5.6%).
In accordance with the 2014 data provided by the International Monetary Fund (IMF), Korea's GDP per capita is 14,495 (one hundred million/$), which is 0.08 times lower than 174,163 (one hundred million/$) of the U.S.A. and 0.30 times lower than 47,698 (one hundred million/$) of Japan [35]. The monthly average income per household as researched by the Korea National Statistical O ce (KOSTAT) in 2014 was 4,302,000 KRW. In the index of ve income brackets depending on income level, the low income class belongs to the rst bracket and its monthly average income was 1,460,000 KRW, the second bracket's monthly average income was 2,866,000 KRW, the third bracket's monthly average income was 3,917,000 KRW and the fourth bracket's monthly average income was 5,136,000 KRW. The high income class belongs to the fth bracket and its monthly average income was 8,129,000 KRW [36].

Discussion
For anyone, there are 24 hours in a day. As a quantitative size, time of a day is given to everyone equally, but people have different ways of spending a day. Also, the quality of time may be different, even though the same amount of time is given to individuals and it is affected by the limitations of their nancial conditions and their environments [37]. This study classi ed healthy older adult subjects in the ROK into an OB group and an OI group using the data of the 2014 KTUS by the KOSTAT. We conducted this study to investigate whether there are differences in time use for occupation by category (eight in total) and the factors affecting the life satisfaction of the OB group.
As a result, the time use according to the type of occupation was the highest in IADL, followed by rest, sleep, and ADL respectively. IADL is an activity that supports daily living at home and community, requiring more complex interactions than activities primarily used in ADL. For example, it includes care, home care, shopping, religious and spiritual activities, food preparation and cleaning, driving and community mobilization. The Korean older adults are found to spend the greatest amount of time in a day doing IADL and leisure activities, which are static activities indoors. Speci cally, this agrees to the result of foregoing studies that the older adults spend most of their time doing everyday household chores as IADL and some other time taking care of a grandchild or a family member as well [20].
As a result of comparing the time use, ADL, IADL, rest and sleep, leisure, work, play, and social participation showed signi cant differences, while time use for education showed no signi cant difference. The largest ES was social participation (1.38), followed by leisure (0.66), IADL (0.59), and work (0.51). Thus, the activity areas with the largest time use difference between the two groups were social participation, followed by leisure, IADL, and work. The OB group showed a higher amount of time use than the OI group in leisure, IADL, rest and sleep, and ADL while a lower amount of time-use than the OIG in work, play, and social participation. This aligns with foregoing studies which reported that the older adults who have enjoyed continued leisure activities show a lower tendency of depression and higher satisfaction with everyday life than those who don't participate in leisure activities, regardless of their type [38].
Compared to the OI group, the OB group spent more time in ADL, IADL, rest and sleep, and leisure and less time in occupational, play, and social participation. This result contradicts the result of the study referring to social participation and proper occupation in old age, which are related to mutual exchange with other people, as essential elements for improving and maintaining the life satisfaction of older adults [39]. According to socioemotional selectivity theory (SST), the aged consciously reduce the frequency of social contact to spend more time on the emotionally compensating relationship, such as family or friends. Therefore, the aged belonging to the OB group are found to seek to enhance life satisfaction by reducing social networks selectively. Based on SST, this study proposes that in developing social relationship activity services for the older adults' life satisfaction, they minimize emotional risk and maximize positive emotional experience by spending more time with close friends or family members, rather than forming new relationships.
As a result of analyzing the factors affecting life satisfaction of the OB Group, we con rmed the following. Higher life satisfaction corresponded to those younger, females more than males, higher levels of education, lower need for care, higher income, and agricultural residence. This is consistent with the study result by Jeon which discovered that the younger, and more females than males, the more use of living time of the occupational balance type, and the study result which discovered that the younger, the more active, and that the more females than males, the higher the level of basic activities and instrumental activities [3].
The effects of cultural factors such as education level and residence area on time use are also reported in various forms. It is pointed out that the in uence of cultural factors such as education level and environment of individual in relation to leisure is greater than that of economic factors such as income and occupation. This is because, through education, one can maintain a high level of stimulation, culture, and insight necessary for leisure activities [40]. This result is consistent with that of the studies which discovered that the higher the level of education, the higher the life satisfaction of older adults in the expectation that the persons with higher education have better nancial status and higher life satisfaction than usual [41]. In other words, the higher the economic and educational level of older adults are, the more important and decisive the close relationship with self-development and socio-cultural activities is to the life satisfaction of older adults [39]. The result of this study shows that as average monthly household income becomes higher, daily life satisfaction is higher, too, despite the insigni cance of economic activity status. It also implies that based on SST, we can have a broader span of social choice that can optimize older adults' psychological and emotional satisfaction. It agrees with the foregoing studies on successful aging in Korea in that the older adults' diverse economic and social activity of production are very important components of successful life in one's declining years [3].
We can estimate the hours of living in the type of occupational balance with the amount of the time used through analyzing the data of 2014 Time Use Survey of the KOSTAT. Many studies on occupational balance have reported that it makes an important in uence on human life satisfaction and health [10,14,15]. Therefore, it will be possible to increase older adults' life satisfaction and health by developing lifestyle redesign programs for them, and other methods to provide an opportunity for balance. For successful aging, one needs training that can distribute living time appropriately as well as help from a time intervention specialist to make it a habit.
This study has limitations in investigating the satisfaction and importance of time use in KTUS as well as in understanding the use of living time according to the social environment and characteristics of individuals. We expect that future surveys of living time may supplement the limitations. In addition, since sociocultural differences among the countries have some effect on the living time of older adults, future studies should analyze the factors determining the OB based on the theories of sociocultural differences among nations in terms of living time use. Though this study was a survey made on healthy older adults, absence of a measure of health can be a limitation. In foregoing studies reviewing the in uence of health condition on life satisfaction, the satisfaction with health felt subjectively was one of the important variables that predicted life satisfaction [42]. It is considered that in future studies, there will be need to compose logic by applying variables with a measure of subjective and objective health conditions. This study has signi cance in that it analyzed the living time of older adults over 65 years of age in terms of occupational type, and this analysis will help the clients with di culty in time use as well as healthy elders perform their daily tasks in the way of occupational performance. Various methods should be suggested to maintain the OB for the successful aging of older adults.

Conclusions
Based on the results of this study, we identi ed the relationship among occupation, old age, health and life satisfaction, so that we can effectively establish old-age preparation plans for the current older adults' generation as well as future older adults' generations. We expect that the results will have important implications as a basis for use mediation and program development. This study may be generalized because it ensured objectivity by using the raw materials from the living time research by the KOSTAT, rather than personally veri ed and researched time data. This study may provide a basis for the development of time-use management and lifestyle redesign programs in order for older adults to practice the disease prevention and health maintenance roles by themselves.