Abstract
Near falls (NFs) are more frequent than falls, and may occur before falls, potentially predicting fall risk. As such identification of a NF is important. We aimed to assess intra and inter-rater reliability of the traditional definition of a NF and to demonstrate the potential utility of a new definition. To this end, 10 older adults, 10 idiopathic elderly fallers, and 10 patients with Parkinson’s disease (PD) walked in an obstacle course while wearing a safety harness. All walks were videotaped. 49 video segments were extracted to create 2 clips each of 8.48 minutes. Four raters scored each event using the traditional definition and, two weeks later, using the new definition. A fifth rater used only the new definition. Intrarater reliability was determined using Kappa (K) statistics and inter-rater reliability was determined using ICC. Using the traditional definition, three raters had poor intra-rater reliability (K<0.054, p>0.137) and one rater had moderate intra-rater reliability (K=0.624, p<0.001). With the traditional definition, inter-rater reliability between the four raters was moderate (ICC=0.667, p<0.001). In contrast, the new NF definition showed high intra-rater (K>0.601, p<0.001) and high inter-rater reliability (ICC=0.815, p<0.001). A priori, it is easy to distinguish falls from usual walking and NFs, but it is more challenging to distinguish NFs from obstacle negotiation and usual walking. Therefore, a more precise definition of NF is required. The results of the present study suggest that the proposed new definition increases intra and inter-rater reliability, a critical step for using NFs to quantify fall risk.
Keywords: fall risk, near falls, gait, aging
INTRODUCTION
Self-reported near falls (NFs) are related to fall risk1–4, are more frequent than falls1, 3, 4, and indeed may precede falls2, 3. One can assume, therefore, that NFs are clinically relevant markers of fall risk and that measuring their frequency may help to provide a broader, more robust estimate of fall risk. The traditional definition (Table 1)3–5 is pragmatic, has face validity, and is useful for self-report. To date, this definition has been used in most studies of NFs.
Table 1.
Near falls definitions
| Definition | Additional components to assist with identification |
|
|---|---|---|
| Traditional definition | A stumble event or loss of balance that would result in a fall if sufficient recovery mechanisms were not activated | |
| New Definition* | A stumble event or loss of balance that would result in a fall if sufficient recovery mechanisms were not activated. At least two of the following compensatory mechanism should be activated to be determined as a near fall. | Possible compensatory mechanisms: (1) unplanned movement of arms or/and legs (2) unplanned change in stride length (3) lowering of the center of mass (4) unplanned change in stride velocity (5) trunk tilt |
The definition was based on careful review of video tapes that included near falls, falls, usual walking, and obstacle negations in healthy adults, elderly fallers, and patients with Parkinson’s disease. The goal was to develop a simple-to-use, but more sensitive definition that could reliably distinguish these different events. During the review process, the key role of compensatory mechanisms in a near fall became evident. Since the presence or absence of specific compensatory mechanisms apparently helped to distinguish near falls from other events, they were included in the new definition.
With the advent of small, light-weight body-worn sensors that can be applied in the home and community settings and with the push for mobile- mHealth solutions6, automatic detection of NFs with devices worn continuously may be feasible6. This possibility has potential advantages of improved sensitivity, accuracy, and reliability. Before this can be achieved, it is important to re-consider the traditional definition of a NF. Several protocols have been developed to produce NFs in the laboratory setting, a necessary step towards continuous monitoring of NF6. Negotiating obstacles, for example, is used to provoke NFs. During obstacle negotiation, adjustments of the gait pattern such as changes in speed, step length, and rhythm may occur7–9. Assessing these changes may not be trivial as the gait pattern may be altered with aging and disease10–12. These alterations may look similar to a NF, challenging identification. Additionally, during a NF, compensatory mechanisms may be utilized, further increasing the challenge. To address these issues, we propose a new definition that extends the traditional definition by including several possible compensatory mechanisms that may be activated to avoid a fall (Table 1). This study aims to assess intra and inter-rater reliability of the traditional NF definition and demonstrate the potential use of this new definition in the development of methods for automatically detecting and quantifying NFs objectively.
METHODS
Evaluators
Five raters participated in this study: (1) a senior physical therapist researcher, (2) an experienced neurologist, (3) a senior research engineer, and two (4, 5) physical therapists. Three raters were familiar with the topic of falls and therefore represent “experienced assessors”, while the other two raters were new to this topic and represented a more “naïve” viewpoint. All five raters were not involved in the development of the new definition.
Procedures
To provoke NFs under laboratory conditions, we created an obstacle course that included two types of obstacles: 10 meters of an uneven surface covered with a carpet and two transparent wires one meter before and after the carpet. Three groups of subjects were included: 10 healthy older adults, 10 idiopathic fallers, and 10 patients with Parkinson’s disease (PD) (Table 2). After providing informed written consent as approved by the local ethics committee, the participants walked up and down a 30 meter long corridor while wearing a safety harness under three conditions: 1) comfortable walking, 2) obstacle course walking, and 3) obstacle course walking while simultaneously subtracting serial 3s. During the protocol, the examiner walked behind the subject to assure safety and to document the timing and occurrence of any events (e.g., NFs). The protocol was videoed with one frontal plane camera.
Table 2.
Participant characteristics
| Subject Group |
Age (years) |
Gender (male/female) |
Falls in the year prior to testing |
Hoehn and Yahr stage |
# of Fallers* in the Group |
Gait speed (m/sec) |
|---|---|---|---|---|---|---|
| Healthy older adults* (n=10) | 79.8±4.6 | 4/6 | 0.21±0.42 (range: 0–1) | Not applicable | 0 | 1.23±0.22 |
| Idiopathic fallers (n=10) | 77.8±5.0 | 5/5 | 4.50±3.36 (range: 2–12) | Not applicable | 10 | 1.02±0.23 |
| Patients with Parkinson’s disease (n=10) | 60.7±9.2 | 8/2 | 0.16±0.39 (0–2) | 2–3 | 1 | 1.18±0.1 |
Older adults were classified as fallers if they reported falling 2 or more times in the past year. Otherwise, they were considered as healthy older adult, non-fallers.
Forty-nine video segments, each of 5 seconds, were extracted: 4 of obstacle negotiation, 3 of falls, and 42 possible NFs. An 8.48 min movie was created from these segments: 23 segments from healthy older adults, 14 from fallers, and 12 from patients PD, from conditions 2 and 3. To assess test retest reliability, the first four raters rated each segment using the traditional definition. Then they watched the movie again, this time with the order of the segments randomized to assess test re-test reliability. Two weeks later, the segments were rated again using the new definition. The fifth rater classified the segments only according to the new definition to assess the possibility that reliability was impacted by the repeated assessments. Eight video segments are included in the online supplementary material as examples of events that were reviewed and rated to assess reliability of the traditional and new definition.
Data analysis
Intra-rater analysis was performed for each definition separately by calculating the Kappa statistic (K) between the two clips. A K value over 0.75 was considered excellent, 0.40–0.75 as fair to good, and below 0.40 as poor13. Inter-rater reliability was determined by calculating the ICC for the four and five raters when the traditional and new definitions were used, respectively. Since the raters classified two movies for each definition, two ICCs were calculated, one for the first movie and one for the second. The average of these two ICCs was calculated for each definition. Scores between 0–0.2 indicated poor agreement; 0.3–0.4 fair agreement; 0.5–0.6 moderate agreement; 0.7–0.8 strong agreement; and >0.8 excellent agreement14. Statistical analysis was performed using SPSS version 17.
RESULTS
Reliability using the traditional definition
Intra-rater reliability of three raters was poor, K = (−0.211)−0.054, p >0.137, while one rater had fair to good reliability, K= 0.624, p<0.001. The inter-rater reliability between the participating four raters was moderate, ICC= 0.67, p<0.001.
Reliability using the new definition
Intra-rater reliability of the five raters was high, K= 0.601–0.959, p<0.001. The inter-rater reliability between the five raters was fair to good, ICC= 0.815, p<0.001.
Comparison between the reliability of the traditional definition and the new definition
Intra-rater reliability increased from poor to good when the new definition was applied (Figure 1A). In addition, inter-rater reliability increased from moderate to strong when the new definition was applied (Figure 1B).
Figure 1.
A) Intra rater reliability using the traditional definition and the new definition of a near fall. B) Inter rater reliability using the traditional definition and the new definition of a near fall.
DISCUSSION
We examined whether a definition of a NF based on five possible compensatory mechanisms that commonly appear when recovering from a loss of balance improves the consistency and reliability of NF identification. The present findings demonstrate that the new definition increases intra and inter reliability among raters compared to the traditional definition15. To our knowledge, the reliability of the traditional definition was never explicitly tested. The present results indicate that this definition is not highly reliable and that a more precise definition is needed. The higher intra-rater reliability for the new definition indicates that the use of specific criteria for a NF increases consistency across raters.
The evaluation of NFs is challenging. In laboratory conditions, NFs are difficult to provoke, may not necessarily imitate real life, and may vary across individuals, environmental conditions, and obstacle types. On the other hand, self-report of NFs, as has been done in the past3, 4, is subjective, relies on motivation and recall, typically requires a long observation period (e.g., weeks/months), and lacks sensitivity. New methods that can automatically detect and quantify NFs in a more objective way in the community and at-home settings may address the limitations of self-report and laboratory testing6. To progress in this direction, a critical first step is to improve the NF definition, as proposed here. Evaluating the role of the compensatory mechanisms involved in a NF seems likely to enhance the identification process. A better understanding will also help to guide the placement of the sensors on the body and the accuracy of NF identification. The new definition is an important step forward for augmenting the study of NFs in the laboratory and community settings and should help in the development of the automatic identification of NFs, ultimately, providing a more reliable tool for understanding and assessing fall risk.
Supplementary Material
1. An older adult with a history of multiple falls with no apparent cause (i.e., idiopathic faller) is seen successfully stepping over a transparent wire. He slows down before the wire. Since it is a planned change in the gait pattern, this reduced gait speed is not considered a compensatory mechanism in response to a loss of balance. This is considered successful obstacle negotiation, but is not a near fall.
2. A patient with Parkinson’s disease (PD) steps over a transparent wire and continues walking on an uneven surface covered with a carpet. No changes in gait speed are observed. This is considered successful obstacle negotiation, but not a near fall.
3. A fall in a patient with PD that is caused by tripping on a transparent wire. No compensatory mechanisms were activated and he would have found himself on the floor if the safety harness was no present.
4. A fall in a healthy older adult that is caused by tripping on a transparent wire. No compensatory mechanisms were activated and she would have found herself on the floor if the safety harness was not present.
5. While walking on an uneven surface, a patient with PD changes his gait pattern. Only one compensatory mechanism was activated, i.e., lowering of the center of mass. Therefore, this is not considered a near fall.
6. When walking on an uneven surface, an idiopathic elderly fallers walks with a very slow and cautious gait pattern. All the changes in gait pattern are planned. Therefore, this is not a near fall; the compensatory mechanisms were not activated in response to a loss of balance.
7. A near fall in a healthy older adult occurs while walking on an uneven surface. Three compensatory mechanisms were activated: unplanned changes in stride length, velocity, and forward trunk tilt.
8. A near fall in an idiopathic elderly faller occurs while walking on an uneven surface. Three compensatory mechanisms were activated: unplanned changes in stride length, velocity, and sideward trunk tilt.
ACKNOWLEDGEMENTS
This work was supported in part by the National Institute on Aging (5R21AG034227), the Israel Science Foundation, and the European Commission (FP7-ICT-2011-7 – ICT-2011.5.4 - Contract no. 288878).
We thank the staff and patients of the Tel Aviv Sourasky Medical Center's Movement Disorders Unit for invaluable assistance.
Footnotes
Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
REFERENCES
- 1.Arnold CM, Faulkner RA. The history of falls and the association of the timed up and go test to falls and near-falls in older adults with hip osteoarthritis. BMC Geriatr. 2007;7:17. doi: 10.1186/1471-2318-7-17. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Ashburn A, Hyndman D, Pickering R, Yardley L, Harris S. Predicting people with stroke at risk of falls. Age Ageing. 2008;37:270–276. doi: 10.1093/ageing/afn066. [DOI] [PubMed] [Google Scholar]
- 3.Srygley JM, Herman T, Giladi N, Hausdorff JM. Self-report of missteps in older adults: a valid proxy of fall risk? Arch Phys Med Rehabil. 2009;90:786–792. doi: 10.1016/j.apmr.2008.11.007. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Stack E, Ashburn A. Fall events described by people with Parkinson's disease: implications for clinical interviewing and the research agenda. Physiother Res Int. 1999;4:190–200. doi: 10.1002/pri.165. [DOI] [PubMed] [Google Scholar]
- 5.Gray P, Hildebrand K. Fall risk factors in Parkinson's disease. J Neurosci Nurs. 2000;32:222–228. doi: 10.1097/01376517-200008000-00006. [DOI] [PubMed] [Google Scholar]
- 6.Weiss A, Shimkin I, Giladi N, Hausdorff JM. Automated detection of near falls: algorithm development and preliminary results. BMC Res Notes. 2010;3:62. doi: 10.1186/1756-0500-3-62. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Lowrey CR, Reed RJ, Vallis LA. Control strategies used by older adults during multiple obstacle avoidance. Gait Posture. 2007;25:502–508. doi: 10.1016/j.gaitpost.2006.05.012. [DOI] [PubMed] [Google Scholar]
- 8.Means KM, Rodell DE, O'Sullivan PS. Obstacle course performance and risk of falling in community-dwelling elderly persons. Arch Phys Med Rehabil. 1998;79:1570–1576. doi: 10.1016/s0003-9993(98)90423-3. [DOI] [PubMed] [Google Scholar]
- 9.Yang F, Bhatt T, Pai YC. Generalization of treadmill-slip training to prevent a fall following a sudden (novel) slip in over-ground walking. J Biomech. 2013;46:63–69. doi: 10.1016/j.jbiomech.2012.10.002. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Baltadjieva R, Giladi N, Gruendlinger L, Peretz C, Hausdorff JM. Marked alterations in the gait timing and rhythmicity of patients with de novo Parkinson's disease. Eur J Neurosci. 2006;24:1815–1820. doi: 10.1111/j.1460-9568.2006.05033.x. [DOI] [PubMed] [Google Scholar]
- 11.Hausdorff JM, Cudkowicz ME, Firtion R, Wei JY, Goldberger AL. Gait variability and basal ganglia disorders: stride-to-stride variations of gait cycle timing in Parkinson's disease and Huntington's disease. Mov Disord. 1998;13:428–437. doi: 10.1002/mds.870130310. [DOI] [PubMed] [Google Scholar]
- 12.Morris ME, Huxham FE, McGinley J, Iansek R. Gait disorders and gait rehabilitation in Parkinson's disease. Adv Neurol. 2001;87:347–361. [PubMed] [Google Scholar]
- 13.Wallenstein S, Fleiss JL, Chilton NW. The logistic analysis of categorical data from dental and oral experiments. Pharmacol Ther Dent. 1981;6:65–78. [PubMed] [Google Scholar]
- 14.Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics. 1977;33:159–174. [PubMed] [Google Scholar]
- 15.Wiles CM, Busse ME, Sampson CM, Rogers MT, Fenton-May J, van Deursen R. Falls and stumbles in myotonic dystrophy. J Neurol Neurosurg Psychiatry. 2006;77:393–396. doi: 10.1136/jnnp.2005.066258. [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
1. An older adult with a history of multiple falls with no apparent cause (i.e., idiopathic faller) is seen successfully stepping over a transparent wire. He slows down before the wire. Since it is a planned change in the gait pattern, this reduced gait speed is not considered a compensatory mechanism in response to a loss of balance. This is considered successful obstacle negotiation, but is not a near fall.
2. A patient with Parkinson’s disease (PD) steps over a transparent wire and continues walking on an uneven surface covered with a carpet. No changes in gait speed are observed. This is considered successful obstacle negotiation, but not a near fall.
3. A fall in a patient with PD that is caused by tripping on a transparent wire. No compensatory mechanisms were activated and he would have found himself on the floor if the safety harness was no present.
4. A fall in a healthy older adult that is caused by tripping on a transparent wire. No compensatory mechanisms were activated and she would have found herself on the floor if the safety harness was not present.
5. While walking on an uneven surface, a patient with PD changes his gait pattern. Only one compensatory mechanism was activated, i.e., lowering of the center of mass. Therefore, this is not considered a near fall.
6. When walking on an uneven surface, an idiopathic elderly fallers walks with a very slow and cautious gait pattern. All the changes in gait pattern are planned. Therefore, this is not a near fall; the compensatory mechanisms were not activated in response to a loss of balance.
7. A near fall in a healthy older adult occurs while walking on an uneven surface. Three compensatory mechanisms were activated: unplanned changes in stride length, velocity, and forward trunk tilt.
8. A near fall in an idiopathic elderly faller occurs while walking on an uneven surface. Three compensatory mechanisms were activated: unplanned changes in stride length, velocity, and sideward trunk tilt.