As detailed in Fig. 1, our analysis included 9279, 6153, 4142, 4148, and 3583 eligible adults aged 60 years and older who completed follow-up assessments after 2, 3, 4, 5, and 7 years, respectively. The fall incidence among older adults per 100 person-years was 9.7% (95% CI: 9.3–10.1%) at the 2-year follow-up, 7.4% (95% CI: 7.0-7.7%) at the 3-year follow-up, 8.0% (95% CI: 7.6–8.4%) at the 4-year follow-up, 7.0% (95% CI: 6.7–7.4%) at the 5-year follow-up, and 6.2% (95% CI: 5.9–6.5%) at the 7-year follow-up. The corresponding fall-induced injury incidence per 100 person-years at the five follow-up time periods was 6.0% (95% CI: 5.6–6.3%), 4.6% (95% CI: 4.3–4.9%), 6.0% (95% CI: 5.6–6.3%), 5.4% (95% CI: 5.1–5.7%), and 5.4% (95% CI: 5.2–5.7%) (Appendix Table 2).
As hypothesized, both fall incidence and fall-induced injury incidence decreased significantly as SPPB performance increased at all five follow-up time periods, P<0.05 (Fig. 2). After adjusting for sex, age group, ADL, history of fall in the past 2 years, depression, stroke, memory-related disease, sensory status, muscle weakness, and cognitive function, the SPPB performance was significantly associated with fall incidence only at the 4- and 5-year follow-up time periods, P<0.05 (Table 1). After adjusting for the same covariates, SPPB performance was significantly associated with fall-induced injury at the 2, 5, and 7-year follow-up time periods (Table 2).
Table 1
Association of SPPB performances with fall incidence rates at different follow-up time periods
Follow-up time
|
SPPB performance
|
Number of person-years
|
Number
|
Incidence (%, 95% CI)
|
OR (95% CI)
|
2 years
|
High
|
12506
|
1111
|
8.9% (8.4%-9.4%)
|
1.00 (Ref.)
|
|
Medium
|
4828
|
510
|
10.6% (9.7%-11.4%)
|
1.01 (0.89–1.15)
|
|
Low
|
1224
|
176
|
12.6% (10.8%-14.3%)
|
1.19 (0.97–1.47)
|
3 years
|
High
|
15189
|
1041
|
6.9% (6.5%-7.3%)
|
1.00 (Ref.)
|
|
Medium
|
2610
|
237
|
9.1% (8.0%-10.2%)
|
1.04 (0.87–1.25)
|
|
Low
|
660
|
79
|
12.0% (9.5%-14.5%)
|
1.21 (0.88–1.67)
|
4 years
|
High
|
10336
|
743
|
7.2% (6.7%-7.7%)
|
1.00 (Ref.)
|
|
Medium
|
4888
|
421
|
8.6% (7.8%-9.4%)
|
1.10 (0.94–1.29)
|
|
Low
|
1344
|
156
|
11.6% (9.9%-13.3%)
|
1.42 (1.10–1.84) *
|
5 years
|
High
|
15440
|
1014
|
6.6% (6.2%-7.0%)
|
1.00 (Ref.)
|
|
Medium
|
4515
|
352
|
7.8% (7.0%-8.6%)
|
0.99 (0.84–1.17)
|
|
Low
|
785
|
88
|
11.2% (9.0%-13.4%)
|
1.54 (1.08–2.19) *
|
7 years
|
High
|
16006
|
917
|
5.7% (5.4%-6.1%)
|
1.00 (Ref.)
|
|
Medium
|
7224
|
474
|
6.6% (6.0%-7.1%)
|
1.02 (0.87–1.20)
|
|
Low
|
1841
|
157
|
8.5% (7.3%-9.8%)
|
1.31 (0.99–1.75)
|
Notes: |
1. SPPB: Short Physical Performance Battery. |
2. Fall incidence rate was calculated as “(number of persons who experienced at least a fall / number of person-years◊100%)”. |
3. OR: Odds ratio, which was calculated after adjusting for sex, age group, ADL, history of fall in the past 2 years, depression, stroke, memory-related disease, sensory status, muscle weakness, and cognitive function. |
4. 95% CI: 95% confidence interval. |
5. *: P < 0.05 |
Table 2. Association of SPPB performances with fall-induced injury incidence rates at different follow-up time periods
Follow-up time
|
SPPB performance
|
Number of person-years
|
Number
|
Incidence (%, 95% CI)
|
IRR (95%CI)
|
2 years
|
High
|
12506
|
644
|
5.1% (4.8%-5.5%)
|
1.00 (Ref.)
|
|
Medium
|
4828
|
319
|
6.6% (5.9%-7.3%)
|
1.04 (0.89-1.21)
|
|
Low
|
1224
|
143
|
11.7% (9.9%-13.5%)
|
1.45 (1.16-1.81) *
|
3 years
|
High
|
15189
|
625
|
4.1% (3.8%-4.4%)
|
1.00 (Ref.)
|
|
Medium
|
2610
|
170
|
6.5% (5.6%-7.5%)
|
1.12 (0.92-1.37)
|
|
Low
|
660
|
47
|
7.1% (5.2%-9.1%)
|
0.98 (0.69-1.41)
|
4 years
|
High
|
10336
|
552
|
5.3% (4.9%-5.8%)
|
1.00 (Ref.)
|
|
Medium
|
4888
|
311
|
6.4% (5.7%-7.0%)
|
1.01 (0.86-1.19)
|
|
Low
|
1344
|
126
|
9.4% (7.8%-10.9%)
|
1.15 (0.90-1.48)
|
5 years
|
High
|
15440
|
714
|
4.6% (4.3%-5.0%)
|
1.00 (Ref.)
|
|
Medium
|
4515
|
322
|
7.1% (6.4%-7.9%)
|
1.18 (1.00-1.38) *
|
|
Low
|
785
|
79
|
10.1% (8.0%-12.2%)
|
1.32 (0.97-1.80)
|
7 years
|
High
|
16006
|
765
|
4.8% (4.4%-5.1%)
|
1.00 (Ref.)
|
|
Medium
|
7224
|
427
|
5.9% (5.4%-6.5%)
|
1.05 (0.90-1.21)
|
|
Low
|
1841
|
173
|
9.4% (8.1%-10.7%)
|
1.32 (1.05-1.66) *
|
Notes:
1. SPPB: Short Physical Performance Battery.
2. Fall-induced injury incidence rate was calculated as “(number of fall-induced injury / number of person-years◊100%)”.
3. 95% CI: 95% confidence interval.
4. IRR: incidence rate ratio, which was calculated based on negative binomial regression models after adjusting for sex, age group, ADL, history of fall in the past 2 years, depression, stroke, memory-related disease, sensory status, muscle weakness, and cognitive function.
5. *: P<0.05.
The goodness-of-fit of predictive models using the SPPB performance as a single predictor was particularly low for both study outcome events across five follow-up time periods -- Cox-Snell R2: 0.003–0.011; Nagelkerke R2: 0.001–0.016; and accuracy: 0%-11.1% for participants experiencing at least one fall or fall-induced injury, 94.8%-100% for participants not experiencing a fall or fall-induced injury, and 58.2%-91.6% for all participants combined. When using the SPPB performance and other variables as predictors together, the corresponding goodness-of-fit performance of predictive models was: Cox-Snell R2: 0.02–0.076; Nagelkerke R2: 0.046–0.104; and accuracy: 0%-37.5% for participants experiencing at least one fall or fall-induced injury, 80.7%-100% for participants not experiencing a fall or fall-induced injury, and 62.1%-91.6% for all participants combined (Table 3). Subgroup analyses by sex and age group demonstrated highly similar predictive performance (Appendix Tables 3 and 4).
Table 3
Goodness-of-fit of predictive models for falls and fall-induced injuries based on multivariable logistic regression
Outcome event
|
Follow-up time
|
Model
|
Cox-Snell R2
|
Nagelkerke R2
|
Accuracy (%)
|
Participant A
|
Participant B
|
Combined
|
Fall
|
2 years
|
Model 1
|
0.005
|
0.008
|
0
|
100%
|
80.6%
|
|
|
Model 2
|
0.044
|
0.071
|
0.8%
|
99.7%
|
80.6%
|
|
3 years
|
Model 1
|
0.007
|
0.001
|
0
|
100%
|
77.9%
|
|
|
Model 2
|
0.067
|
0.103
|
11.1%
|
97.5%
|
78.4%
|
|
4 years
|
Model 1
|
0.011
|
0.016
|
0
|
100%
|
68.1%
|
|
|
Model 2
|
0.056
|
0.079
|
17.6%
|
93.4%
|
69.2%
|
|
5 years
|
Model 1
|
0.010
|
0.014
|
6.1%
|
97.4%
|
65.4%
|
|
|
Model 2
|
0.076
|
0.104
|
24.8%
|
91.6%
|
68.2%
|
|
7 years
|
Model 1
|
0.011
|
0.015
|
10.1%
|
94.8%
|
58.2%
|
|
|
Model 2
|
0.059
|
0.079
|
37.5%
|
80.7%
|
62.1%
|
Fall-induced injury
|
2 years
|
Model 1
|
0.003
|
0.006
|
0
|
100%
|
91.6%
|
|
|
Model 2
|
0.020
|
0.046
|
0
|
100%
|
91.6%
|
|
3 years
|
Model 1
|
0.003
|
0.007
|
0
|
100%
|
90.6%
|
|
|
Model 2
|
0.027
|
0.059
|
0
|
100%
|
90.6%
|
|
4 years
|
Model 1
|
0.007
|
0.011
|
0
|
100%
|
84.9%
|
|
|
Model 2
|
0.030
|
0.052
|
0
|
100%
|
84.9%
|
|
5 years
|
Model 1
|
0.007
|
0.011
|
0
|
100%
|
83.8%
|
|
|
Model 2
|
0.040
|
0.067
|
0.1%
|
99.9%
|
83.7%
|
|
7 years
|
Model 1
|
0.010
|
0.015
|
0
|
100%
|
78.0%
|
|
|
Model 2
|
0.040
|
0.062
|
1.7%
|
99.2%
|
77.8%
|
Notes: |
1. Model 1 was fitted by including Short Physical Performance Battery (SPPB) performance as a single predictor. |
2. Model 2 was fitted by including SPPB performance, ADL, history of fall in the past 2 years, depression, stroke, memory-related disease, sensory status, muscle weakness, and cognitive function as predictors. |
3. The statistical test was significant for all predictive models at the 0.05 significance level. |
4. Participant A denotes those experiencing a fall or a fall-induced injury at least once during the follow-up time period; participant B denotes those not experiencing a fall or a fall-induced injury during the follow-up time periods; and the combined category denotes the combination of participants A and B. |
In addition, the area under the ROC curve for using the SPPB score as a single predictor ranged between 0.53 and 0.57 for predicting both fall and fall-induced injury across the five follow-up time periods for both sexes (Appendix Table 5). While using the SPPB score and other predictors simultaneously, the area under the ROC curve for predicting fall and fall-induced injury increased to a range of 0.61–0.67. Age-specific analyses for the 60–69 years and 70 years and older groups displayed highly similar results (Appendix Tables 6 and 7).