This study rejects the hypothesis that allowing cane use while measuring self-selected walking speed introduces poor consistency and fails to find evidence that allowing a cane introduces a systematic measurement difference. We found that SSWS measured among individuals who used a cane was consistent, or reliable. The fact that cane use was seen only at slower walking speeds probably contributes to this consistency. The within-subject CVs suggest a reassuringly low level of test-repeat variability such that measured SSWS is a reasonable estimation of “true” SSWS. The ICCs reported here can be correctly interpreted as indicating that measured SSWS also meaningfully distinguishes between individuals. In other words most of the observed variation is due to differences between individuals, which is most often of clinical interest. In addition, SSWS measured with a cane has comparable systematic variability to SSWS recorded without an aid, such that a second trial tends to be faster.
Our findings support and extend prior work on the test-retest reliability of SSWS, which reports similar reliability in 230 healthy older individuals (ICC 0.903).[14
] This finding held even among the slower individuals who use a cane during the test. In addition, this test has been found to be responsive[15
] and to provide a reliable and objective measure of function over days or weeks.[16
Pending data from a definitive investigation of SSWS tested both with and without a device in individuals who report cane use during daily activities, our findings can reasonably lead to several recommendations for measurement of SSWS in older adults. First, we suggest that researchers and clinicians permit individuals to use their customary cane rather than exclude them from the test. Second, it is important that researchers and clinicians record whether a device was used during the SSWS test. It is noteworthy that our multivariate models of relationships to the mobility disability measures showed that observed device use remained significant in one case and borderline significant in the other, and had a larger coefficient than reported device use, suggesting that it is a marker of elevated likelihood of disability. Third, based on the small systematic tendency for the second trial to be faster than the first, and the amount of these differences (), we recommend that protocols include two trials of walking speed. Finally, SSWS testing with and without a device in the same individual may be informative, as a significant proportion of individuals who use a cane do not use it all the time and it may be that device use alters the course of activity and disability in those individuals.
A limitation of this study is that it does not have the data that would most directly examine the potential effect of device use on measurement variability: SSWS with and without a device for the same individual. To our knowledge, such data have not been published. This is probably because there has been little to no research on individuals who use mobility devices intermittently and safety concerns may prohibit such examinations in a number of those subjects. We also note that the possibility of a type II error in interpreting the large P-value for the interaction term in our models of effect modification. Our analysis of over 850 older adults failed to find an effect, but this is not proof of an absence of effect. Another limitation of this study is that analysis is limited to cane use. The results may be different for other aids.
An important possibility not addressed in this paper is that individuals who chose to use their device during testing were more likely to have walking impairments than individuals who used no aid. Assistive devices for walking are not usually adopted by individuals with intact walking ability, probably because they do not add to their comfort or efficiency of walking under normal conditions. The findings here support other studies showing that device use is associated with poor performance, not just on walking speed but on aid-independent objective measures such as repeated chair stands.[18
] The individuals who chose to use their device during testing may also be systematically different in other important ways. Though they are slower on average, it is unknown whether device use contributes to a poorer prognosis. Subsequent work to determine whether accounting for device use during testing improves the predictive power of SSWS may be fruitful.
In summary, this observational study of older women found no substantial evidence of loss of consistency nor increased measurement bias in self-selected walking speed recorded while using a cane compared to no assistive device.
What is new?
|Key finding:||-Self-selected walking speed (SSWS) recorded while an older|
person used a cane was consistent.
|What this adds to|
what is known:
|-Among older women who used a cane in daily life, roughly half|
chose to use a cane during SSWS testing.
|-Cane use was not associated with loss of consistency (neither|
substantially increased Coefficient of Variation nor decreased
Intra-Class Correlation Coefficient).
|Implications:||-Researchers and clinicians may permit people to use a customary|
cane while recording SSWS.