Developing and testing a new outcome measure.

Kathryn E. Roach, PhD, PT; Alison A. Linberg, DPT, ATC; Michele A. Raya, PhD, PT, SCS, ATC Health outcome measures are used to assess treatment effectiveness. Historically, survival was the most important health outcome. Treatments were assessed based on whether the patient lived or died. Now in the 21st century, treatments for many injuries and illnesses are so effective that many, if not most, patients survive. If patients survive, the quality of their survival becomes an important health outcome. The severity of impairments in body structure (limb loss) and function (weakness) are one way to assess the quality of survival. However, from the perspective of the patient, discomfort and disability are probably more important health outcomes. Limitation in mobility activities is an important component of disability, particularly for individuals with lower-limb loss (LLL). The treatment effectiveness of the rehabilitative care provided to servicemembers with LLL should be assessed by examining its effect on mobility limitations. Unfortunately, it is much more difficult to accurately measure mobility limitations than it is to measure survival. Measurement requires developing a set of rules to assign numbers to represent a concept or health outcome. When outcome measures contain multiple items, rules must also be developed to combine item scores to generate total and subscale scores. Determining the set of rules that will best represent a particular health outcome is affected by both the reason for measuring the outcome and the types of individuals being measured. Outcome measures can be used to examine small changes resulting from a treatment or to place individuals into broad categories. The purpose for using the outcome measure will dictate the types of items selected and the measurement dimension attached to these items. Measures of mobility activity limitations can be either performance-based or self-report. The types of individuals being measured will often determine which approach is best. A performance-based outcome measure requires both a set of rules for performing the test and a set of rules for scoring the test. It is not enough to simply create an outcome measure. It is essential to determine whether the rules used to create the outcome measure work to consistently and accurately represent the concept being measured.