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Physical therapists focus much of their attention toward restoring a patient's functional status. However, a substantial amount of time also is spent screening for previously undiagnosed disease and measuring the extent of impairment. Therefore, there are many times when therapists include impairment and disease-related measures as well as person-level measures of activity limitation and participation restriction during outcome assessment.

Thus far, this book has examined outcome assessment from a broad perspective and, in the context of the theoretical frameworks presented in Chapter 2, outcome measures cover the gamut from disease status, to physical and psychosocial impairment, to person-level activity limitation and participation restriction. Of critical importance is the concept that these various outcome measures are not necessarily strongly related to one another. When we measure one outcome, for example, joint range of motion physical impairment, this measurement should not serve as a surrogate for a different ICF domain, for example, activity limitation.

A strong argument can be made for measuring multiple ICF domains during a plan of care. Hypotheses guiding treatment planning, for example, may focus on restoring strength and range of motion, say, in a patient with low back pain or spinal cord injury. Strength and range-of-motion impairment measures provide critical information to guide the therapist in determining the potential impact of their interventions on these presumably important impairments resulting from the inciting disease or injury. However, the relationship between these impairment measures and the patient's activity limitations or participation restrictions is likely not very strong. For example, Hazard and colleagues found that the Pearson product moment correlation between strength and ROM impairments and disability as measured with the Oswestry Low Back Pain and Disability Questionnaire1 was 0.40 for men and 0.52 for women.2 Correlations among pain and ROM impairment measures were also in this moderate range. These data suggest that physical impairment, pain, and disability outcome measures for patients with low back pain capture different attributes of a patient's recovery and cannot be used as substitutes for each other.

Similar moderate associations between physical impairment measures and person-level activity limitation or participation restriction have been found for a variety of disorders. For example, Rantanen and colleagues found that knee extensor strength explained only 42.3% of the variation in maximum walking speed in elderly women with a variety of disorders.3 In addition, relationships among physical impairments such as strength and ROM and activity limitations such as gait speed are not as straightforward as they may appear. Sometimes they demonstrate a nonlinear relationship, suggesting that one should not assume a more straightforward linear relationship among impairment and disability.4 The take-home message from this substantial body of literature examining relationships among ICF domains is that these domains are typically only moderately related and sometimes related in a complex, nonlinear way. Our view based on this literature is that outcome measures of one domain should not be assumed to ...

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