The ROC curve results were similar for data obtained from participants who initially used an assistive device to walk and for data obtained from participants who could not walk independently (Table 6). Using the participants GROC score as the anchor for participants who used an assistive device to walk at baseline, the AUC of the ROC curve was 0.80. This resulted in an estimated clinically important change in gait speed of 0.175 m/s. Using the physical therapists' GROC score as the anchor for participants who used an assistive device to walk at baseline, the AUC of the ROC curve was 0.64. This resulted in an estimated clinically important change in gait speed of 0.190 m/s. Using the participants' GROC score as the anchor for participants who could not walk independently at baseline, the AUC of the ROC curve was 0.85. This resulted in an estimated clinically important change in gait speed of 0.130 m/s. Using the physical therapists' GROC score as the anchor for participants who could not walk independently at baseline, the AUC of the ROC curve was 0.71. This resulted in an estimated clinically important change in gait speed of 0.185 m/s.
There are limitations of using a GROC scale to determine the threshold for important change in outcome measures. Participants may have difficulty recalling their initial status when reporting on change in ability on the GROC scale.29,30 They may instead report on their current status. However, in this sample of people with stroke, it appeared that they were able to accurately report on change in walking ability on the GROC to some degree. There were significant differences in change in some of the gait characteristics between stroke survivors who were categorized as improved compared with those who were categorized as stable/not improved based on their GROC scores. In addition, the GROC is a global scale. It asked participants to rate their overall improvement in walking ability; however, gait speed is just one aspect of walking ability. Some participants with stroke and therapists perceived that their walking ability improved, but this was not reflected in a change in gait speed. Other aspects of gait may have improved such as requiring less assistance or a more normal walking pattern.
Another limitation of this study is the relatively small sample size used to estimate the important change in gait speed, although other studies that have used a GROC scale for the anchor of important change have used similar sample sizes.38,49 The estimated important change values reported here should be used only with individuals with similar characteristics. Most of the participants in this study had a mild to moderate stroke, as evidenced by the fact that most subjects would be classified as limited community ambulators on the basis of their gait speed.17 We did not control for the type of assistive device used when measuring gait speed. At both the initial and discharge gait speed measurement participants walked with the assistive device they were using at that time. Any potential change in assistive device to one that was less-supportive may have impacted their gait speed. However, in clinical practice, physical therapists often prescribe less-supportive assistive devices as patients improve. Of the 19 participants in this study who changed from an assistive device to either no assistive device or a less-supportive one, only 3 had a decrease in gait speed at discharge.
Estimated clinically important change values are likely to vary depending on the baseline scores of the outcome measure.29,30,50 Individuals with an initial low score on an outcome measure may need only a relatively small amount of change for it to be important. If we considera patient who has an initial gait speed of 0.15 m/s and improves to 0.30 m/s, this change represents a doubling of the patient's gait speed and may be important, but it does not exceed the estimated important change threshold of 0.175 m/s. This criterion score for important change in gait speed should only be used with patients that have characteristics that are similar to the participants of this study.
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