3.1 Total candidates and characteristics
Of the 1,355 participants who received usual care in public health settings, those participants who had a follow-up period of less than three years were excluded. Among individuals, 233 people were excluded because the follow-up period was less than three years. By then, 336 participants dropped out due to either medical reasons (n=170) or follow-up loss (n=166). Among the medical reasons, 35 participants had died, 103 were admitted to nursing homes, and 32 moved out due to health problems. Of the 166 participants with follow-up loss, 53 moved out due to other problems, 89 declined to participate, and 24 had lost contact. Finally, 786 participants who completed routine measurements for three years were analyzed in this study (Figure 1). For participants with a follow-up period longer than three years, the baseline point was defined as the first measurement after enrollment.
Figure 1. Participant selection flow.
* Among the 170 participants who dropped out for medical reasons, 35 participants (20.6%) had died, 103 participants (60.6%) were admitted to nursing homes due to deterioration of health, and 32 participants (18.8%) had moved or were withdrawn due to health problems.
** Among the 166 participants who dropped out due to follow-up loss, 53 participants (31.9%) moved due to other problems (except for health), 89 participants (53.6%) declined to participate, and 24 participants (14.5%) had lost contact.
Participants’ baseline demographic factors including age, gender, education (in years), living alone (or not), and medical aid (or not) were examined according to total participants based on Figure 1 (Table 1). Geriatric conditions such as number of comorbidities, MMSE-DS, number of regular medications, FRAIL scale, SPPB score, CES-D score, MNA-SF score, and the number of falls were included. The average age was 73.3 years (SD: 5.8), and the percentage of females was 52.7% of the total. The average education (in years) was 5.2 years (SD: 3.3), and 15.8% of the total were living alone. Among geriatric conditions, the baseline of the SPPB and MMSE-SD score was 8.8 (SD: 2.8) and 25.7 (SD: 3.9), respectively, each at baseline.
Table 1. Demographic characteristics and geriatric conditions by total participants (456 lines).
3.2. Disability Trajectories
Three trajectory groups were defined according to the degree of disability by the number of impaired domains from the 1st to the 3rd years (Figure 2). The model with three trajectory groups was the best fit for our data based on BIC, considering the proportions of each group (see Table S1 on Additional file 1). The average posterior probability was assigned to each group (p = 0.9, 0.82, and 0.96, respectively) [39].
The “relatively-stable group” (78.5 %; n=617) was characterized by the lowest levels of disability. The “gradually-aggravated group” (16.0 %; n=126) was characterized by slightly increasing levels of disability over time. The remaining 5.5% of the population (n=43) with high baseline disability that was also rapidly aggravating over time were categorized as the “rapidly-deteriorated” group (Figure 2) [40].
Figure 2. Trajectory group of disability over time (with 95% C.I., for 3-years).
3.3. Comparisons of Characteristics Among Trajectory Groups
We looked at factors such as baseline demographic factors and geriatric condition according to the trajectory group likewise in chapter 3.1. (Table 2).
Geriatric measurements differed significantly in the three groups, except for living alone and the number of falls in the 3rd year. In the 1st year, the relatively-stable group had a mean age of 72.1 years, 45.1% were female, the mean number of comorbidities was 1.1, the number of medications was 2.2, and the mean number of falls in the previous year was 0.1. In the rapidly-deteriorated group, mean age at 1st year was 81.1 years (which is almost nine years higher than the relatively-stable group), and 76.7% of the participants were female. This group had a mean number of 2.0 for comorbidities, 4.4 for those receiving regular medications, and 0.8 for the number of falls in the previous year.
In terms of physical performance, the SPPB score was 9.5 points in the relatively-stable group and 3.3 points in the rapidly-deteriorated group. In the 3rd year, the difference between the relatively-stable group and rapidly-deteriorated group was larger than that of the 1st year, increasing from 6.1 to 7.2, respectively.
Table 2. Demographic characteristics and geriatric conditions by trajectory group (458 lines).
3.4. Comparison of Home Time Between the Conventional Versus Trajectory-based Group
Home time decreased by an incremental degree in both the conventional and trajectory-based disability groups (Table 3). Compared to the 1st year, the trend of decreasing home time took place continuously in the 2nd and 3rd year.
In the 1st year, the home time of the severe group was shorter by 8.9 days (352.2 days-343.3 days) compared to the no dependency group by conventional grouping. In contrast, the rapidly-deteriorated group had 11.7 days fewer (351.6 days-339.9 days) home time than the relatively-stable group by trajectory-based grouping in the 1st year.
In the 3rd year, the home time of the severe group was shorter by 5.5 days (350.3 days-344.8 days) compared to the no dependency group by conventional grouping. By trajectory-based grouping, the rapidly-deteriorated group stayed 8.5 fewer days in their home than in the relatively-stable group (350.3 days-341.8 days, a 2.43% decrease).
Table 3. Home time difference according to conventional versus trajectory-based grouping of disability.
Ye-
ar
|
Conventional Disability Group
|
Trajectory-based Group
|
No dependency group (n=518)
|
Mild-dependent group (n=154)
|
Severe-dependent group (n=114)
|
p value*
|
Relatively-stable group (n=617)
|
Gradually-aggravated group (n=126)
|
Rapidly-deteriorated group
(n=43)
|
p value*
|
Home time (days)**, mean (SD)
|
1st year
|
352.2
(14.3)
|
348.0 (22.3)
|
343.3
(23.1)
|
<.001
|
351.6 (14.9)
|
346.0
(19.7)
|
339.9
(37.0)
|
0.003
|
2nd year
|
352.0
(14.1)
|
347.7 (22.2)
|
342.9
(22.8)
|
<.001
|
351.4 (14.7)
|
345.7
(19.5)
|
339.5
(36.4)
|
0.002
|
3rd year
|
350.3
(17.6)
|
348.2 (22.2)
|
344.8
(20.4)
|
0.025
|
350.3 (17.6)
|
345.5
(17.5)
|
341.8
(34.6)
|
0.009
|
* The p value given in the table uses the one-way ANOVA.
3.5. Incidence Rate Ratio for Home Time According to Conventional Versus Trajectory-based Grouping of Disability
After recognizing the differences in home time decrements by definitions of disability phenotype (Table 2), regression models were employed to adjust for demographic factors, including age and gender, in these observations. Additionally, the year of measurement was adjusted in the conventional group since the trajectory-based definition already took into account time sequence. In the statistical model with adjusted variables, significant differences of home time between the conventional based and trajectory-based definitions were observed in the univariate analysis (see Table S2 in Additional file 1).
The IRR for home time in the conventional groups and trajectory groups is shown in Figure 3. Home time in the mild dependent group (IRR = 0.993; 95% CI, 0.987-0.999) was shorter than the reference group (no dependency group) by conventional grouping. Similarly, the severe-dependent group had shorter home time (IRR = 0.985; 95% CI, 0.979-0.992) compared to the no dependency group.
In the trajectory-based group, the home time of the gradually-aggravated group was shorter (IRR =0.992; 95% CI, 0.985-0.999) compared to the relatively-stable group. Similarly, the rapidly-deteriorated group had shorter home time (IRR =0.978; 95% CI, 0.967-0.988) compared to the relatively-stable group.
Figure 3. Forest plot of the incidence rate ratio for conventional versus trajectory group of disability.
*The analysis of the trajectory group was adjusted for gender and age. The conventional group was additionally adjusted for the year of measurement.
** The reference value of the conventional group is the ‘no dependency group’ and the reference value of the trajectory group is the ‘relatively-stable group’
3.6. Incidence Rate Ratio of subgroup for Home Time According to Trajectory-based Grouping of Disability
We also conducted subgroup analysis according to age and gender, respectively. In the case of age group, we divided age group criteria into (1) 65-74 years, and (2) 75 years or older based on [41]. According to our findings, home time in the female group was lower in the gradually-aggravated group and rapidly-deteriorated group than in the relatively-stable group (IRR, 0.989 and 0.967). However, in the male group, there were no significant results for either classification of disability and home time.
In the case of the age group, the IRR for home time in the 65-74 year age group was 0.915 in the rapidly-deteriorated group compared to the relatively-stable group. The portion of the rapidly-deteriorated group was just 1.7% of the total, however. In the 75 years or older group, the disability classification was proper. But it was not statistically significant with regard to home time (see Table S3, Figure S1, and S2).