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Validation of Fear of Falling and Balance Confidence Assessment Scales in Persons With Dystonia

Boyce, Melani J. BAppSc (Phty) (USyd), MAppSc (Phty) (USyd); Lam, Lawrence BSc (Hons) Pharmacology (Liverpool), MAppPsych (Macquarie), GradDipBiostats, MPH, PhD (Epi) (Sydney); Chang, Florence MBBS (Hons) (UNSW), FRACP; Mahant, Neil MBBS (USyd), FRACP, PhD; Fung, Victor S. C. MBBS (Hons) (USyd), FRACP, PhD; Bradnam, Lynley Dip Phty (Auck), MHSc (Hons), PhD

Author Information
Journal of Neurologic Physical Therapy: October 2017 - Volume 41 - Issue 4 - p 239-244
doi: 10.1097/NPT.0000000000000198

Abstract

INTRODUCTION

Falls are prevalent in older adults1 and persons with neurological movement disorders including Parkinson disease2,3 and multiple sclerosis,4–6 causing many secondary medical issues. In addition to actual falls, older people and those with neurological conditions have been found to have high fear of falling, which can predict falls and impact function and participation in daily life.7–10 Much research into understanding falls, their impact and prevention in neurological movement disorders, has focused on people with Parkinson disease and multiple sclerosis.2,4,5,11–13 Dystonia is considered the third most common movement disorder after Parkinson disease and essential tremor.14 Despite this prevalence, there is little understanding as to whether people who live with dystonia experience falls, the frequency of falls, or how falls impact function and participation.

Dystonia can involve isolated body areas such as the neck, hand, or foot, a region such as the upper or lower limb, or can present as “generalized” affecting most of the body.15 Dystonia is generally considered not to directly affect postural control, unless the dystonia involves the lower limbs.16 However, evidence is emerging that people with cervical dystonia (CD), an isolated dystonia of the neck,15,17 have low falls self-efficacy, defined as “the degree of confidence a person has in performing common activities of daily living without falling,”18 which can be measured using the Falls Self-Efficacy Scale (FES).18

Many people with CD have a fear of falling that discourages participation in physical activity.19 Low self-rated balance confidence, measured by the Activities-specific Balance Confidence (ABC) Scale was found in people with CD and blepharospasm, a dystonia affecting eye muscles.20 Considering that low falls self-efficacy has been reported in other neurological populations,21,22 it is possible that people with dystonia also fear falling and have an increased falls risk; before this can be explored, scales to assess fear of falling and balance confidence must be validated in this population.

The Falls Self-Efficacy Scale International (FES-I) and the ABC have been validated for use in many clinical populations, including multiple sclerosis,12,23 Parkinson disease,24 and in healthy older adults.25–27 The primary aim of this study was to validate the FES-I and the ABC in people with dystonia. A secondary aim was to determine cutoff points for falls risk based on retrospective falls history. Validation of these scales for use in persons with dystonia will allow future assessment of fear of falling, falls risk, and negative impact on function. In the longer term, physical therapy interventions to address factors contributing to fear of falling can be developed.

METHODS

This study was approved by the University of Technology Sydney Human Research Ethics Committee (UTS HREC ETH15-0096) prior to commencement. Data were collected via online surveys (Qualtrics Research Suite, Qualtrics, Sydney) delivered to people with dystonia who participated in Internet support groups in Australia and New Zealand. The survey was completed during a 4-week period in November 2015. Included in the survey were questions on demographics, type of dystonia, time since diagnosis, treatment with botulinum toxin, current medications, history and number of falls (based on recall) in the previous 6 months, perceived reason for falling, the Functional Disability Questionnaire (FDQ), the FES-I, and the ABC. The FDQ asks respondents to determine the extent to which their dystonia affects their engagement in, or enjoyment of, 27 daily tasks. Scores range between 0 and 108, with higher scores indicating greater functional disability. The FDQ has been shown to have high internal consistency (α = 0.92) for disability associated with dystonia,28 and has been used to determine disability in the CD population.28,29 The FDQ was used to determine the convergent validity of the FES-I and the ABC in the dystonia population.

Falls Self-Efficacy Scale International

The FES-I is a 16-item self-reported questionnaire testing a person's level of concern about falling during a range of common daily activities. Originally developed for use in the elderly, scores range from 16 to 64, and cutoff points for low (16-19), moderate, (20-27), and high concern (28-64) have been defined.26 The FES-I has excellent internal validity (Cronbach α = 0.96) and test-retest reliability (intraclass correlation coefficient = 0.96) in these groups.25

Activities-specific Balance Confidence Scale

The ABC is a self-reported questionnaire designed to assess a person's confidence in his or her balance while performing 16 common daily tasks.30 Participants rate on a scale of 0% (no confidence) to 100% (complete confidence) how confident they are that they can perform various activities without losing their balance or becoming unsteady. Total scores are determined by the accumulated average of each item score and range between 0 and 100, with lower scores indicating greater impairment of balance confidence. In a longitudinal study of community-dwelling older people, a cutoff point for identifying people at risk of falling was identified as lower than 67%,8 with lower ABC scale scores correlating with lower levels of mobility30 and falls.8 High retest reliability has been reported in the same population (r = 0.92).30 In Parkinson disease, the ABC scale was shown to have good test-retest reliability (intraclass correlation coefficient [3,1] = 0.79; 95% confidence interval [CI]: 0.57-0.90) and good validity.24

Psychometric Analyses

The psychometric properties, including the validity of both scales, were examined in this study. Since both scales were designed and validated as a single construct instrument, to examine the structural validity, Confirmatory Factor Analysis (CFA) was conducted using the Structural Equation Model approach with the Maximum Likelihood methods on the sample. The goodness-of-fit of different models to the data was examined using multiple criteria. These included the Reduced χ2 statistics (χ2/df), Comparative Fit Index (CFI), Root-Mean-Square Error of Approximation (RMSEA), and the Akaike Information Index with a χ2/df less than 5, CFI greater than 0.90, RMSEA less than 0.05, and a lower Akaike Information Index indicating a better fitted model.31 The internal consistency of the FES-I and ABC was evaluated using Cronbach α and the item-total correlations. Convergent validity was also examined with interinstrument correlations between FES-I, ABC, and the FDQ. Predictive validity of the 2 scales was also examined by comparing scores obtained on the FES-I and the ABC between participants with and without a history of falls as well as sexes using independent t tests.

To further investigate the diagnostic value of these 2 scales in the dystonia population, the cutoff points of the scales for determining falls risk were also calculated using receiver operating characteristic (ROC) curves, determined by falls history. Missing data were treated by the addition of average values but only when missing data did not exceed 25% of the total.19 No data were excluded on the basis of this criterion. Statistical analyses were performed using SPSS for Windows, Version 22 (SPSS, Inc., Chicago, Illinois) with a type I error rate of 5% for all hypothesis testing.

RESULTS

One hundred and twenty-two participants responded to the demographic questions. Of these, 118 people (96%) completed the FDQ, 114 people (93%) completed the FES-I, and 108 people (88%) completed the ABC. The characteristics of respondents and their average scores on each scale are shown in Table 1. Just more than 71% of respondents reported a diagnosis of CD, spasmodic dysphonia, and facial or upper limb dystonia (ie, dystonia not affecting the lower limbs, either segmental or generalized). The average scores were FES-I: 31.4 ± 13.3, and ABC: 67.4 ± 27.2. Of the total 122 respondents, 48 (39%) reported a history of falls in the previous 6 months and 74 (61%) reported no falls history.

Table 1 - Participant Characteristics (n = 122)
Characteristic Mean (SD) Range, CI, or %
Age, y 52 (12.4) Range: 18-76
Gender
Male: 21 17%
Female: 101 83%
Time since diagnosis, y 9 (9.1) Range: 0.4-53
Dystonia type
CD 65 55.1%
Segmental/focal UL 6 5.1%
Segmental/focal LL 2 1.7%
Facial dystonia/blepharospasm 8 6.8%
Generalized dystonia 16 13.6%
Multisegmental 15 12.7%
Spasmodic dysphonia 6 5.1%
Botulinum toxin injections
Yes 72 59%
No 50 41%
Psychoactive medication
Yes 69 56.6%
No 53 43.4%
Experienced a fall in last 6 mo
Yes 48 39.3%
No 74 60.7%
Functional Disabilities Questionnaire 82.6 (17.46) CI: 78.79-85.45
Falls Self-Efficacy Scale (FES-I) 31.4 (13.30) CI: 28.88-33.95
Activities Balance Scale 67.4 (27.21) CI: 62.23-72.13
Abbreviations: CD, cervical dystonia; CI, confidence intervals; LL, lower limb; UL, upper limb.

Validation of the FES-I

The CFA was conducted on the data with comparisons of a single factor model with all items included to the independent model. The results obtained from the model fits are summarized in Table 2. As shown, the model fit statistics of the single factor model did not fully satisfy all preset criteria, with a weaker performance in the results obtained on the CFI and the RMSEA while maintaining a reasonably good-fit statistics for other criteria. All items achieved a high factor loading ranging from 0.79 to 0.89, with 67% of variance of the data explained by the model (Table 3).

Table 2 - Goodness-of-Fit Statistics Obtained From the Confirmatory Factor Analysis for Model Fits of the FES-I and the ABC
Scale χ2/df CFI RMSEA AIC AIC of Independent Model
FES-I 3.8 0.86 0.16 463 2074
ABC 5.7 0.76 0.21 655 2146
Abbreviations: ABC, Activities-specific Balance Confidence Scale; AIC, Akaike Information Index; FES-I, Falls Self-Efficacy Scale International; RMSEA, Root-Mean-Square Error of Approximation.

Table 3 - Factor Loading of Each Item in the Scale and Other Psychometric Information of FES-I and ABC
Item FES-I ABC
1 0.88 0.77
2 0.78 0.74
3 0.80 0.90
4 0.80 0.84
5 0.89 0.78
6 0.80 0.65
7 0.78 0.89
8 0.84 0.88
9 0.79 0.90
10 0.78 0.93
11 0.75 0.83
12 0.87 0.84
13 0.85 0.82
14 0.81 0.77
15 0.80 0.61
16 0.87 0.58
Total variance explained 67% 64%
Abbreviations: ABC, Activities-specific Balance Confidence Scale; FES-I, Falls Self-Efficacy Scale International.

The Cronbach α of the FES-I was 0.97, suggesting a good to an excellent internal consistency of the scale. The item-total correlations and the Cronbach α change after deleting the item of the FES-I were tabulated in Table 4. As shown, all items were strongly correlated to the total scale, with correlation coefficient ranging from 0.78 to 0.87. Deletion of an item did not improve the consistency of the scale, indicating that all items should be retained. Convergent validity was examined by the correlation between the FES-I and FDQ, yielding a correlation coefficient of 0.77 (P < 0.001) suggesting a moderately strong and positive correlation between the 2 measures.

Table 4 - Internal Consistency, Item-Total Correlations, and Cronbach α if Item Was Deleted From the Scale for FES-I and ABC
FES-I (n = 114) ABC (n = 107)
Item Item-Total Correlation Cronbach α if Item Deleted Item-Total Correlation Cronbach α if Item Deleted
1 0.86 0.97 0.70 0.97
2 0.77 0.97 0.77 0.96
3 0.78 0.97 0.85 0.96
4 0.79 0.97 0.76 0.96
5 0.87 0.97 0.81 0.96
6 0.78 0.97 0.70 0.96
7 0.78 0.97 0.82 0.96
8 0.82 0.97 0.81 0.96
9 0.78 0.97 0.84 0.96
10 0.78 0.97 0.90 0.96
11 0.76 0.97 0.82 0.96
12 0.84 0.97 0.85 0.96
13 0.83 0.97 0.85 0.96
14 0.82 0.97 0.82 0.96
15 0.80 0.97 0.70 0.97
16 0.84 0.97 0.64 0.97
Total Scale 0.97 0.97
Abbreviations: ABC, Activities-specific Balance Confidence Scale; FES-I, Falls Self-Efficacy Scale International.

While there was no significant difference between the means of men and women, the mean score of FES-I for those who had a history of falls was significantly higher than those without a history (t = 5.5, P < 0.01) (Table 5). For the clinical diagnostic value, the ROC analysis was conducted yielding an area under the curve of 0.76 (95% CI = 0.67-0.86, P < 0.001), indicating a moderate sensitivity and specificity for predicting the risk of a fall. Based on the predictive values provided by the curve, a cutoff at a value of 29.5 could provide the optimal sensitivity of 67% and a specificity of 73% for the instrument to predict the history of falling.

Table 5 - Means and Standard Deviations of FES-I, ABC, and FDQ by Sex and History of Falls
Variable FES-I ABC FDQ
Sex
Male 32 (14) 67 (27) 83 (19)
Female 30 (13) 72 (24) 79 (17)
Falls history
Yes 40 (15)a 55 (28)a 88 (21)b
No 26 (9) 75 (22) 79 (16)
Abbreviations: ABC, Activities-specific Balance Confidence Scale; FDQ, Functional Disability Questionnaire; FES-I, Falls Self-Efficacy Scale International.
aP < 0.01.
bP < 0.05.

Validation of the ABC

The structural validity of the ABC was investigated with data subjected to the CFA with a single factor as the default model in comparison to the independent model. The results of the CFA are provided in Table 2. Similar to the FES-I, the model fit statistics of the single factor model for ABC did not fully satisfy all preset criteria, with a weaker performance also in the CFI and the RMSEA while maintaining a reasonably good-fit statistics for other criteria. On the contrary, all items achieved a relatively high factor loading with a minimum of 0.58 and a maximum of 0.93, with 64% of variance of the data explained by the single factor model (Table 3). The Cronbach α of the ABC was 0.97, reflecting good to excellent internal consistency. The item-total correlations and the Cronbach α change after deleting the item of the ABC were also tabulated in Table 4. Results suggested a strong correlation between each item and the total scale and no item deletions improved the performance of the scale.

Convergent validity was examined by the correlation between the ABC and the FDQ, with a correlation coefficient of 0.65 (P < 0.001), indicating moderate correlation between the 2 measures. Similar to the FES-I, no significant differences were observed in the mean score of the ABC between men and women. However, participants who had a history of falls scored significantly lower than those who had never had a fall (t = −3.6, P < 0.01) (Table 5). The ROC analysis was also conducted with an area under the curve of 0.72 (95% CI = 0.62-0.82, P < 0.001). A cutoff at the value of 71.3 yielded a sensitivity of 66% and a specificity of 36% to predict the falls history.

DISCUSSION

This is the first study to assess the validity of the FES-I and ABC scales in people with dystonia. Our main findings were that both scales have high internal validity, convergent validity with the FDQ, and report a single factor of fear of falling (FES-I) and balance confidence (ABC) in people with dystonia. Therefore, the FES-I and the ABC can be used to examine fear of falling and balance confidence in the dystonia population. The total mean scores for the scales indicate that fear of falling is high and confidence in balance is low in people with dystonia and is worse in those who have already fallen. The contributing reasons why people with dystonia fall and the impact of falling related fear on function and on future falls risk are yet to be explored. The validation of these scales will support such research and assist to identify therapeutic interventions aimed at improving fear of falling and balance confidence in the dystonia population.

Moderate sensitivity and specificity for predicting a fall in people with dystonia was found in both scales. Our ROC analysis indicated that a cutoff point to predict falls using the FES-I was 29.5 points. Interestingly, our whole group average score was 31 points, indicating low falls self-efficacy in dystonia. When comparing these data to other populations who fall, an FES-I score above 23 points was reported in healthy elderly,26 an FES-I score of 25 points was reported in people with multiple sclerosis,21 and an FES-I score of 29.5 points was reported for people with Parkinson disease.22 These data suggest that the low falls self-efficacy in dystonia is similar in other populations who experience falls.

All preset criteria for the CFA were not met for the results obtained on both scales. The sample size of the study is relatively small in view of the number of items of both scales included in the analyses, which might have impacted the results on the fitness statistics due to a lower degree of variability in responses. The lack of power of the study owing to small sample size is also compounded by missing data in some of the item variables; this might have contributed to further misfit of the model. However, given the strong evidence for the construct validity of the these scales, it is unlikely that the small sample size or missing data in the sample would have a large effect on the result obtained.

The findings of our study regarding fear of falling and falls risk in persons with dystonia are interesting in light of the paucity of available literature. A previous study of persons with CD demonstrated that 25% of participants reported fear of falling, although the numbers of actual falls were not recorded.19 As the authors used a different version of the FES, direct comparisons with the current study cannot be made; however, their average FES of 124/130 indicated that falls self-efficacy was also low in their participants.19 The FES-I was used in a study of ten persons with cervical dystonia who reported an average score of 29.5, remarkably similar to the current results.32 There were also low ABC scores reported in a small number of people with CD and blepharospasm.20 Altogether, these studies indicate that fear of falling is high and balance confidence is low in persons with dystonia.

Our ROC analysis indicated that the cutoff to predict falls using the ABC scale was 71.3 points and the group average in the current study was 67 points. Again, this score indicates that balance confidence was generally low in this group of participants living with dystonia. The average score in the current study is lower than the average reported in a small study of people with CD, blepharospasm, and writer's cramp (91 points).20 The average score of 67 is also much lower than ABC scale scores reported for people with Parkinson disease (Hoehn and Yahr stage 3, 81 points)24 and in multiple sclerosis (mean of 79 points).21 However, our cutoff point for predicting falls of 71.3 points in the current study is similar to cutoff point of 67 in the healthy elderly.8 The reason for our lower average scores for the ABC is unclear but may relate to the demographics of people who participated in the survey. One limitation of a survey is that people with significant functional disability or who had experienced a fall may have been more likely to participate in the study. Although we cannot know this for certain, it may have impacted on the findings and resulted in a slightly lower average for the ABC scale. A follow-up study of people with dystonia attending a neurology clinic, ensuring a broad range of functional ability, would clarify this issue. Regardless, these current data indicate that fear of falling, low balance confidence, and falling may be an issue for people living with dystonia, perhaps to a similar degree as in other neurological populations. The FES-I and the ABC scales should be included in clinical assessments of people with dystonia to help determine falls risk and ensure that appropriate interventions are performed.

As this study was conducted as a one-off online survey, a longitudinal follow-up was not possible. Furthermore, the relationship between the scales and physical function measures, such as gait, balance, and mobility, could not be performed. Previous studies indicate that the FES-I and ABC scales correlate with balance measures such as center of pressure sway in people with multiple sclerosis21 and the Timed Up and Go test in Parkinson disease.22 While fear of falling was highly correlated to disability, assessed by the FDQ, further studies are needed to examine whether the FES-I and ABC scales are associated with gait, mobility, and balance function. Ultimately, these scales need to be tested to determine their ability to predict the future risk of falls in a prospective study.

There were several limitations to this study. In addition to reliance on information from people motivated to participate in the study as outlined previously, a second limitation is that those with all types of dystonia were allowed to participate in the survey. Therefore, those with generalized, segmental, and multisegmental dystonia in which dystonia affects the lower limbs, as well as dystonia of the upper quartile were included in the analysis. We did not attempt to categorize the data on the basis of lower limb involvement, as more than half the respondents reported dystonia of the face, neck, or upper limb. What is interesting is that the findings indicate that it is not just lower limb dystonia that causes functional disability or falls. Why people with upper quartile isolated or segmental dystonia experience issues with balance and mobility or fall needs to be carefully explored. In addition, we did not ask participants to report their level of ambulation and so cannot determine whether some were wheelchair dependent or nonambulant. Furthermore, the survey allowed participants to choose their own definition of a fall rather than providing the generally accepted formal definition “an unexpected event in which the participant comes to rest on the ground, floor, or lower level.”18 Therefore, the true rate of falling in this population may be greater or lesser than reported. Finally, falls were reported retrospectively and a follow-up study using prospective falls reporting is needed to confirm the percentage of fallers in the dystonia population.

CONCLUSIONS

This study found that the FES-I and ABC scales have a high internal validity in people with dystonia. This means that these scales can be used to examine fear of falling and balance confidence in the dystonia population. We also demonstrated that people with dystonia have low falls self-efficacy and balance confidence, similar to the healthy elderly and people with multiple sclerosis and Parkinson disease. This, together with the high proportion of participants who reported a history of a fall, indicates that mobility impairment and falls may represent an issue that is more significant than generally appreciated in people with dystonia. Further research is required using these validated scales to help inform understanding of this problem and develop interventions to improve fear of falling and balance confidence that may, in turn, reduce risk of falling.

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Keywords:

falls self-efficacy; human movement system; consistency; receiver operating characteristics

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