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a Division of Geriatrics and Department of Medicine, University of California, San Francisco
b The San Francisco VA Medical Center, California
c Department of Sociology, Case Western Reserve University, Cleveland, Ohio
d Department of Psychology, Cleveland State University, Ohio
e Division of General Internal Medicine and the Department of Medicine, University of Pittsburgh, Pennsylvania
f The VA Pittsburgh Healthcare System, Pennsylvania
Kenneth E. Covinsky, Division of Geriatrics, San Francisco VAMC (111G), 4150 Clement, San Francisco, CA 94121 E-mail: covinsky{at}medicine.ucsf.edu.
Decision Editor: John E. Morley, MB, BCh
| Abstract |
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Methods. We evaluated the risk of falling over a one-year period in 557 elderly persons (mean age 81.6) living in a retirement community. On the baseline interview, we asked subjects if they had fallen in the previous year and evaluated risk factors in six additional conceptual categories. On the follow-up interview one year later, we again asked subjects if they had fallen in the prior year. We evaluated risk factors in the different conceptual categories and used logistic regression to determine the independent predictors of falling over a one-year period. We used these independent predictors to create a fall-risk index. We compared the ability of a prior falls history with other risk factors and with the combination of a falls history and other risk factors to discriminate fallers from nonfallers.
Results. A fall in the previous year (OR = 2.42, 95% CI = 1.493.93), a symptom of either balance difficulty or dizziness (OR = 1.83, 95% CI = 1.162.89), or an abnormal mobility exam (OR = 2.64, 95% CI = 1.644.26) were independent predictors of falling over the subsequent year. These three risk factors together (c statistic = .71) discriminated fallers from nonfallers better than previous history of falls alone (c statistic = .61) or the symptomatic and exam risk factors alone (c statistic = .68). When combined into a risk index, the three independent risk factors stratify people into groups whose risk for falling over the subsequent year ranges from 10% to 51%.
Conclusion. A history of falling over the prior year, a risk factor that can be obtained from a clinical history (balance difficulty or dizziness), and a risk factor that can be obtained from a physical exam (mobility difficulty) stratify people into groups at low and high risk of falling over the subsequent year. This risk index may provide a simple method of assessing fall risk in community-dwelling elderly persons. However, it requires validation in other subjects before it can be recommended for widespread use.
FALLS are common in community-dwelling elderly persons, and those who fall are at higher risk for a number of adverse outcomes (1)(2)(3)(4)(5). For example, Tinetti (3) recently reported that even one noninjurious fall during a one-year period is associated with a three-fold greater risk of nursing home placement. Falls are responsible for most hip fractures in older people and are the leading cause of accidental death in people over age 65 (1)(6). Falls are also associated with increased health care costs and frequently precipitate visits to the emergency room and hospital admission (7). Even seemingly minor, noninjurious falls can be disabling by leading to a fear of future falling, which in turn can result in decreased activity levels (8) and diminished quality of life.
There is evidence that simple interventions may reduce the risk of falling in high-risk elders (9)(10)(11). However, most intervention programs require at least moderate resources and provider time. These resources could be used most efficiently if they were targeted at elderly persons who are at the highest risk of falling. Thus, a simple risk stratification tool that discriminated between patients at high risk of falling (those most likely to benefit from an intervention) and patients at low risk of falling (those least likely to benefit from an intervention) would be of use to physicians and other health care providers.
While a number of studies have determined risk factors for falling (2)(4)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24), only a limited number of fall-risk indices have been published, and few published indices have focused on community-dwelling elderly persons (2)(4)(12)(13)(14)(15)(16)(17)(18)(19)(20). Some of these indices have been restricted either to injurious or recurrent falls (4)(12)(14)(17)(20). Most published indices document the importance of mobility and balance impairments in identifying patients at high risk for falling. For example, Lord (17) demonstrated that performance on tests of static and dynamic balance successfully stratified patients into groups with different risk of falling. Likewise, Maki (19) demonstrated that postural balance was associated with fall risk. Similarly, Studenski (18) demonstrated that a stratification system based on mobility impairment discriminated between patients with a 5% and 23% risk of falling. Environmental characteristics further discriminated between low-risk and high-risk patients. While a prior history of falls was an independent risk factor in patients with high mobility risk, prior falls was not specifically incorporated into the risk index. Robbins (13) has further demonstrated that risk factors identified from a comprehensive history and a physical exam identified patients at high risk of falling; however, this study did not assess the role of a prior falls history. Tinetti (2) demonstrated the importance of considering multiple domains of risk factors by showing that sedative use, cognitive impairment, poor lower extremity function, balance abnormalities, and foot problems all contributed to an index predicting falls. While a prior falls history was also predictive of falls, the developed index did not specifically consider a falls history. Subsequent work demonstrated that this index could be used to identify patients who would successfully respond to an intervention to reduce the incidence of falls (9). Tinetti and colleagues (16) have also recently demonstrated that an index that includes upper-extremity, lower-extremity, sensory, and affective impairments discriminates fallers from nonfallers. Furthermore, this study demonstrated that the risk factors for falls may also be risk factors for other geriatric syndromes, such as functional dependence and incontinence.
The goal of this study was to develop a simple prediction index to stratify community-dwelling elderly persons into groups at different risk for falling over the subsequent year. First, we examined the relationship between risk factors in seven different conceptual categories and subsequent falling. These categories included recent falls history, demographic characteristics, psychosocial characteristics, health status, physical activity, symptomatic risk factors (trouble with balance or dizziness), and physical-examrelated risk factors (mobility impairment). We selected these conceptual categories because each has been demonstrated to be strongly associated with falls or other health outcomes (25)(26)(27)(28)(29)(30)(31). Next, we used logistic regression to determine independent risk factors for falling. In developing these models, we were particularly interested in examining the relative ability of a previous falls history compared with other risk factors that can be obtained from a patient history and physical exam to discriminate subsequent fallers from nonfallers. Finally, we combined independent risk factors into a risk score to stratify subjects into low- and high-risk groups for subsequent falls.
Our hypotheses were (i) multiple domains of risk are required to predict falls; (ii) an index considering both a prior falls history and other risk factors will predict falls better than a falls history or other risk factors alone; and (iii) using the domains outlined above, it will be possible to stratify patients into groups at high and low risk for falling.
| Methods |
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Dependent Variable
The major dependent variable was whether or not the patient reported falling during the previous year on the Year 5 (outcome) interview. A fall was defined as unintentionally coming to rest on the ground.
Independent Variables
Predictor variables included characteristics measured on the Year 4 (baseline) interview that were potential risk factors for falling. We grouped risk factors for falling into seven conceptual categories:
5).
Analyses
We used chi-square tests, modified for trend when appropriate, to measure the association between each risk factor and falls over the subsequent year.
Our goals for the multivariate analyses were to determine independent risk factors for falling and to compare the relative utility of a history of falling, other risk factors, and a combination of a falls history and other risk factors in predicting subsequent falls. Our first model was a logistic regression model that considered only a history of falling. Our second model was a stepwise logistic regression model that considered all risk factors that were associated with falls in the univariate analysis (entry criteria, p < .20; retention criteria, p < .05) other than a falls history. Forward and backward selection models produced the same results. The third model was identical to the second model, except that it also considered falls history for entry. We used the c statistic to measured the ability of each model to predict falling. The c statistic, a commonly used measure of discrimination for predictive models, is the probability that given any random pair of patients, one of whom fell and one of whom did not fall during the subsequent year, the patient who fell would have a higher assigned risk than the patient who did not fall (41).
Clinical Utility of Risk Factors
To examine the clinical utility of the risk factors in our final model, we assigned a risk score to each patient on the basis of the presence or absence of each risk factor. A point value was assigned to each risk factor on the basis of the relative Beta weight of each risk factor in the final model. We then calculated fall rates as a function of the risk score. Finally, we compared the sensitivity, specificity, positive predictive value, and negative predictive values of three alternative indices using different cutpoints. The first "index" considered only whether or not the patient fell in the prior year. The second index considered only whether the patient described a history of balance difficulty or dizziness or had an abnormal mobility exam (independent risk factors from Model 2). The third index considered falls history, history of balance difficulty or dizziness, and abnormal mobility exam.
| Results |
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Predictors of Falling: Multivariate Analyses
While a history of falling in the previous year was associated with falling in the subsequent year (Table 2 ), a model considering only a falls history was only moderately effective in discriminating persons who fell from those who did not fall in the subsequent year (Model 1, c statistic = .61). In a stepwise logistic regression model considering all risk factors other than a falls history, an abnormal mobility exam or a history of balance difficulty or dizziness were independently associated with falling. These risk factors discriminated fallers from nonfallers more effectively (p < .001) than a history of falling (Model 2, c statistic = .68). A model that considered all of these risk factors (Model 3) discriminated fallers from nonfallers better (p < .02) than either model alone (c statistic = .71).
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| Discussion |
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Our risk index, like any risk index developed with multivariate techniques, should be viewed as a parsimonious method of identifying persons at risk for an adverse outcome rather than as a method for identifying the mechanism or important determinants of that outcome. The risk factors we identified in our multivariate model likely represent distal events in the causal chain that leads to falling in elderly persons. However, a number of potentially important causes of falling are not included in the final model because they are predictors of the more distal predictors of falling that were included in our final model. For example, because functional dependence is closely associated with, and may in part cause, abnormal performance on a mobility exam, it is unlikely to be associated with falling after controlling for an abnormal mobility exam. However, preventing functional dependence and treating potential causes of functional dependence such as depressive symptoms may be a more useful long-term method of preventing falls than waiting for people to develop an abnormal mobility exam (28). Similarly, higher levels of physical activity may improve mobility and balance performance. As a result, physical activity levels may not be associated with falling after controlling for mobility and balance. However, increasing levels of physical fitness may still play an important role in preventing falls (11)(31).
While we found that a history of falling in the prior year predicts falling in the subsequent year, we found that a history of balance difficulty or dizziness, together with an abnormal mobility exam, are better discriminators of future fallers than a falls history. Furthermore, all these factors together discriminate fallers from nonfallers better than any single risk factor alone. Our results differ from a recent report in nursing home patients that a falls history is by far the single strongest predictor of future falling (42). This report utilized data from the minimum data set (MDS) and may reflect the possibility that falls are more reliably included in the MDS than are specific risk factors for falling. It is also likely that a prior falls history is a stronger predictor of future falls in a highly dependent nursing home population than in a mostly independent community-dwelling population. Other community-based studies have demonstrated that a prior history of falling is a risk factor for future falling (12)(19)(21). However, we are not aware of community-based studies that explicitly compare the utility of indices that include falls history with indices that include other risk factors for predicting subsequent falls.
Most published fall risk indices differ somewhat from each other because they consider different risk factors in their development (2)(4)(12)(13)(14)(15)(16)(17)(18)(19)(20). For example, not all risk indices consider a previous fall as a risk factor, while others consider risk factors we did not measure, such as specific medications. Virtually all community-based studies have found some measure of mobility or stability to be an important risk factor for falling, although the specific measures used vary between studies (2)(4)(12)(13)(14)(15)(16)(17)(18)(19)(20). For example, Maki (19) demonstrated that measures of postural balance were strongly associated with subsequent falls, while Tinetti (23) demonstrated that simple performance-based tests of balance and mobility predicted subsequent falls. The use of different variables in different studies makes it difficult to compare different indices. While our risk index has fewer variables than other indices, it has the advantage of being conceptually simple and easy to administer. The three variables in the index can be obtained easily during the course of a routine clinical history and examination.
An important limitation of our risk index, along with virtually all other published fall-risk indices, is that the index has not been validated in a patient population that differs from the development sample. As described by Justice (41), the development of a risk index is akin to the development of any scientific hypothesis. Like any scientific hypothesis, a risk index needs to be subjected to the scrutiny of repeated testing. Before recommending a risk index for widespread clinical use, its stability and generalizability should be tested in populations that differ from the development sample. Ideally, these validations should test the generalizability of the index in people with at least moderately different characteristics from those in the development sample, across different intervals of time, and using somewhat different methods of data collection by different investigators (41). We are aware of only one fall risk index, which was developed for use in older hospital inpatients, that has been validated in a population distinct from the development sample (24).
Several limitations of our study should be considered in interpreting our results. First, because we asked respondents to recall falls over a full year, it is possible that they did not recall all their falls. Cummings (43) has previously reported that 13% of patients with documented falls during a 12-month period failed to recall falls when interviewed. This recall bias probably caused us to underestimate the discriminative ability of our risk index. Second, it is possible that some respondents had difficulty distinguishing balance difficulties from actual fall occurrences. Third, our sample was homogeneous in terms of ethnicity, potentially limiting the generalizability of our results. Fourth, we were unable to obtain data on falls among respondents who either died during the index year or who were lost to follow-up.
In conclusion, a simple risk index that includes a history of falling in the prior year, symptoms of dizziness or balance difficulty, and an abnormal mobility exam stratifies people into groups at markedly differing risks of falling over the subsequent year. The discriminative ability of this index is considerably better than an index that just considers a history of falling over the prior year. If validated in other populations and settings, this risk index would provide a simple method of identifying elderly persons at high risk of falling.
| Acknowledgments |
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This project was supported by a merit award from the National Institute on Aging to Dr. Kahana. Dr. Covinsky (a Paul Beeson Faculty Scholar in Aging Research) was supported in part by a clinical investigator award from the National Institute on Aging (K23AG00714) and an Independent Scientist Award from the Agency for Healthcare Research and Quality (K026HS00006-01). Dr. Kahana was supported in part by a Merit Award from the National Institute on Aging. Dr. Justice (a Robert Wood Johnson Generalist Physician Faculty Scholar) was supported in part by a clinical investigator award from the National Institute on Aging (AG 00826-03).
Dr. Schumacher is now with the Gerontology Program, Bowling Green State University, Bowling Green, OH.
Received September 3, 1999
Accepted April 28, 2000
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