Longitudinal trajectory of disability in community-dwelling older adults: An observational cohort study in South Korea

The number of countries facing an aging population is increasing worldwide [1, 2]. The increase in the world’s older population implicates an increase in not only the prevalence of chronic diseases, but also the burden of people with functional impairments and geriatric conditions (e.g., frailty and sarcopenia) [3‐6]. Particularly, disability, which is regarded as a health-related condition, increases care demands and socioeconomic burdens for both families and communities [7‐9].

The onset of disability varies substantially among individuals with similar chronological ages [10‐13]. Studies have shown that differences exist among individuals in terms of presence of multimorbidity, frailty, and disability. Evidence also suggests that disability can be prevented or delayed when accompanied by appropriate multifactorial interventions to remove risk factors and improve functioning, making disability one of the most important outcome measures in studies targeting older populations [14].

The conventional method of assessment for disability focuses on the severity of the disability at the initial diagnosis; however, this does not reflect the individuality and time course of the disability. The trajectory method of assessment focuses on the changes in the later years of life [15]. Previous studies have shown different trajectory models based on mood, physical activity, and disability in the later years of life [8, 15‐17]. However, the trajectory and time course of various disabilities are still not well understood. Although some studies show trajectories and subsequent mortality with disability [15], other studies demonstrate that not all older individuals with disability in the community end up being institutionalized in chronic hospitals or other long-term care facilities [16‐18]. It is unclear whether an older individual identifying with a disability has a high probability of readmission or long-term institutionalization. Furthermore, only a few studies have focused on the dynamic trajectories of disability in community-dwelling older adults [18].

Previously, trajectories of disability were not researched in relation to patient-centered outcomes. Patient-centered outcomes are the result of a healthcare system that prioritizes a patient’s needs in conjunction with the healthcare professional’s medical expertise. It focuses on health status that is meaningful to patients such as quality of life, functional status, and independent living [19‐21]. In recent studies, “home time” has been proposed as a patient-centered measure relevant to the quality of life for older people [22‐24]. Home time, meaning the number of days alive and spent at home, comes from the concept of patients’ wanting to maximize the number of days they can be at home rather than in hospital or nursing facilities at the end of their life. Home time focuses on priority values and purposes that are important to older patients or their families, and shows its relationship with self-rated health, mobility, self-care difficulties, and limited social activity [22‐24].

The objective of this study is to explore the following: (1) how disability is divided by the trajectory method in relation to time-sequenced data in a longitudinal cohort, (2) whether the demographic and geriatric conditions differ among the trajectory groups, and (3) whether home time, a patient-centered outcome, is differentiated by the trajectory groups.

Disability is a major determinant of quality of life in older adults. In the present study, different trajectory groups were categorized according to the severity of disability over time. The conventional method of identifying disability shows only a snapshot of disability status and individual disability components. Therefore, the trajectory groups of disability that we identified demonstrated a more integrated approach toward defining disability.

The major finding of this study is that three trajectory groups with different severities of disability were confirmed in community-dwelling older adults. The three trajectory groups were divided into the following: a relatively-stable group (78.5%), a gradually-aggravated group (16.0%), and a rapidly-deteriorated group (5.5%). Previous studies had shown trajectory grouping using the number of disabilities in patients with underlying diseases such as cancer. In a study with cancer patients, the percentage of the severe trajectory group was 21.2% prior to receiving cancer treatment [42]. Our study is unique in that we show the percentage of the severe disability group (rapidly-deteriorated group) to be around 5.5% in relatively healthy older adults living in rural communities. Our data may serve as a basis for future reference in disability studies of the general older populations.

Another finding is that there were differences in the demographic characteristics and geriatric conditions among the different trajectory groups. Most of the variables of the demographic and geriatric conditions were significantly different trajectory groups, except for the number of falls and living alone status. We confirm that the age increased, and the years of education decreased from the relatively-stable to deteriorated group. What stands out most from this study is the change in SPPB. It is well known that SPPB is an important variable for older adults in addition to the FRAIL scale and MMSE-DS score [43]. Our results show that in the 3rd year, the SPPB score was 10.2 points (SD: 2.0) in the relatively-stable group and 3.1 points (SD: 2.2) in the rapidly-deteriorated (more severe) group. In addition to a statistical difference, the numerical difference shows that there was a difference of more than three times between the relatively-stable group and the rapidly-deteriorated group. From this result, we recommend that a comprehensive geriatric assessment in clinical settings be performed, if available, in order to measure physical performance such as SPPB.

Furthermore, our study contributes to the literature by showing that the trajectory method can maximize the difference in home time compared to the conventional method. We showed that home time decreased more over time, as the disability type was severe at initial diagnosis and the increasing levels of disability were rapid. In the 2nd and 3rd year follow-up, the decrease in home time was smaller than in the 1st year, but the home time of the trajectory groups were still reduced compared to the conventional groups, and this difference was statistically significant. We found that the trajectory method decreased 3.33% in the rapidly-deteriorated group compared to the stable group. In the conventional case, the severe-dependent group decreased by 2.53% compared to the non-dependent group.

The rapidly-deteriorated group had shorter home time (IRR = 0.978; 95% CI, 0.967–0.988) compared to the relatively-stable group by trajectory method. This result was shorter than the severe-dependent group of the conventional method (IRR = 0.985; 95% CI, 0.979–0.992).

Considering subgroup, home time in the female group was lower in the gradually-aggravated and rapidly-deteriorated group than in the relatively-stable group (IRR, 0.989 and 0.967), but males and other age groups were not significant in terms of disability classification or home time reduction.

Finally, our results can inform public health professionals developing care models to detect trajectories of disability and build individualized intervention or rehabilitation programs and health policies based on the trajectories, for older, vulnerable populations.

The strengths of this study are that the enrollment rate was 90% and based on an aging cohort derived from an academic-public health collaborative model. We obtained consistent data based on internationally validated geriatric assessment tools and, therefore, the results reflect real world data. Although our data is based on rural communities where some proportions of individuals have low education and are engaged in agriculture, it is a population-based cohort and the sociodemographic characteristics were similar to those of the representative Korean national data.

This study has several limitations. Among the 1122 eligible participants, 166 people (15%) were lost to follow-up. This may be a limitation in constructing the trajectory model, however, this 15% follow- up loss was over the three years of analysis. Therefore, loss to follow-up occurred around 5% per year, which is less than the general percentage of population migration. Second, there may be a recall bias in home time. The participants may not fully recall their hospital or emergency visits in the previous years. In order to overcome this limitation, we obtained information from Community Health Posts in Pyeonchang run by the National Healthcare Service for information if the participants were not fully aware of their hospital use in the past. Therefore, we attempted to minimize recall bias. Third, there was a relatively short follow-up term. The cohort was a three-year follow-up study and, therefore, there is a need for individuals to be examined over longer periods of time. Lastly, it is difficult to capture the short- and medium-term changes in disability lasting less than a year by the methods we used. Gill et al. have suggested that mechanisms underlying the different subtypes are likely to differ. While the presence of physical frailty increased the likelihood of developing long-term, recurrent, and unstable disability, it only had a modest effect on developing transient and short-term disability [44].

A longitudinal trajectory method was used to apply the time trend of disability to community-dwelling older adults. We verify that the demographical and clinical indexes are different according to the trajectory grouping, and the significant effect of the trajectory method on home time was also examined. Our observations provide public health professionals and policy makers with valuable information in order to set priorities for policy making and intervention.