Author Response

We appreciate the comments of Escorpizo, Cieza, and Stucki¹ on our article,² in which we used the components of the International Classification of Functioning, Disability and Health (ICF)³ as a framework to categorize clinical measures as we explored their accuracy in identifying people with stroke according to fall history. We found the ICF framework practical and useful for this purpose, as the model brings meaning to clinical tools and the constructs they measure. We hope our work will further the translation of the ICF from the theoretical to the practical for these purposes.

Escorpizo and colleagues raise important issues regarding the examination of clinical measures at the broader component level of the ICF, as we did, and the potential value of examining measures according to “Core Sets.”^4,5 The question is whether drilling deeper into a measure according to ICF Core Sets will enhance our understanding of the utility of the instrument for a particular purpose. Taking the Berg Balance Scale (BBS) as an example, Escorpizo and colleagues have accurately pointed out that all of the items of the BBS could be associated with the Core Set of “mobility” (d4), which encompasses transfers and maintaining and changing body positions. We have unpublished data that suggest a small number of items, all related to changing or maintaining body positions and not transfers, are responsible for the discriminative power of the BBS for classifying people based on fall history. These data would suggest that an item-by-item analysis of clinical measures may shed further light onto measurement characteristics that explain their utility for specified purposes. Using Core Sets, as Escorpizo and colleagues suggest, would be an excellent approach. Such an analysis could be done of the Stroke Impact Scale-16 (SIS-16),⁶ where the items are derived from several components of the ICF. One might find that the discriminative power of the SIS-16 as a falls screening tool may be derived from 1 or 2 of the included components and perhaps by a defined number of Core Sets.^4,5 We agree with Escorpizo and colleagues and see potential value in such analyses because they may result in streamlined, briefer measures that may be more accurate than using the whole and may be more efficient for clinical use.

We considered the Activities-specific Balance Confidence (ABC) Scale⁷ to represent personal factors according to the ICF model.² Escorpizo and colleagues have suggested that the ABC Scale also may relate to the “activities and participation” and “environmental factors” components of the ICF. Looking at the activities included in the ABC Scale (questions about walking, reaching, and riding escalators), we understand how they came to this conclusion. We would argue, however, that if one considers the root question of “How confident are you that you can…?”,² it is clear that the ABC Scale measures not an individual's ability to perform a task but rather his or her psychological state of confidence in performing the task. The construct of confidence or self-efficacy is related to the Core Set of “mental functions” (b1) and specifically to the classification of “confidence” (b1266).³ As we explore the relationship between personal factors and mobility, the ICF emphasizes the need to consider both mental and physical body functions. We believe this is a crucial distinction. In fact, the ability to perform a task is not always strongly associated with confidence in performing the task,⁸ indicating that these are distinct constructs. Based on these findings, it remains our opinion that the ABC Scale probably best fits in the “personal factor” component of the ICF. We would welcome further discussion on this important topic.

In conclusion, we agree that the ICF is a useful framework for examining measurement properties of clinical measures. Analysis of clinical measures according to ICF Core Sets may make the model even more useful and may inform our understanding of the discriminative power of clinical tools relative to identifying groups of interest. There is a clear need for more applications in the area of diagnostic testing for physical therapy diagnoses using multiple constructs and core values for a full exploration of the ICF's utility in this area.

• American Physical Therapy Association