**Abstract**

A patient's subjective perception about his/her own functional status and also about health-related quality of life represents a challenge both for clinicians and researches, particularly in the field of rehabilitation. Clinicians often overlook the functional limitations and disability experienced by patients. Because functional limitations and disability are most important to the patient, it is essential that clinicians quantify dysfunction at this level. Client-based assessment instruments, like questionnaires, are tools suitable for comprising the domains of activity and social participation and are often the selected instrument for the assessment of healthrelated quality of life. In this chapter, the main aspects of such outcome measures are discussed in order to help clinicians and researchers in the selection of appropriate assessment tools in their daily practice.

**Keywords:** self-report measures, psychometric analysis, ankle/foot disorders, item response theory, Rasch model
