Understanding the relevance of measured change through studies of responsiveness.

The concept of change is important to clinicians, clinical researchers, and policy makers. Clinicians think about change with each patient encounter. In fact, as Streiner and Norman suggest, the goal of a treatment is often to induce change in patients. Clinicians might then ask many questions about changes they observe in their practice. Was that the expected change (size, direction, and nature of change)? Did it help the patient(s) to feel better? What changes should be expected in patients treated in a certain manner? Clinical researchers and policy makers think about change as they seek evidence of the relative effectiveness of different treatment programs or the ability to reduce program costs without compromising patient health status or quality of life. The patient’s perspective should and often does hold an important place in all these decisions; thus, the need to be able to measure and assess the clinical relevance of the measured change from this perspective also becomes important. Self-report measures of health, symptoms, or other attributes are ways that the patient’s perspective is quantified in a standardized manner. A change score is obtained by the arithmetic differences between serially gathered data—for instance, before and after treatment. Tests of the statistical significance of measured change are often available for these self-report measures; however, they fail to describe the clinical relevance of a change score, and it is this link that would allow these questions to be answered. In fact, it is only when the meaning and clinical relevance of the change score can be interpreted that clinicians, researchers, and policy makers can begin to integrate the perspective gained from patient self-reports into their decision making. The ability of a measure to accurately detect change when it has occurred is called responsiveness. Studies of a measure’s responsiveness link the amount of change in its score with a construct of change—some way of determining that change has in fact occurred. Many different constructs for change have been used: change before and after a treatment of known efficacy or in those persons deemed to be better or worse based on their response to an external marker. Previous work has described a classification system to delineate the different types of change that could be designed into a study of responsiveness. These studies tend to focus on determining a psychometric property of a questionnaire. However, given the close link between the construct of change and the change in the outcome’s scores, studies of responsiveness could also be used as a source of information on the meaning of a given change score. The information on change scores specifically in relation to a given construct could help to anchor interpretation of outcome measures scores. For example, Deyo and Centor reported a mean change in the Roland–Morris Questionnaire (RMQ) of 3 of a maximum of 24 points in a group of patients observed for 3 weeks after onset of acute low back pain. In the same study a change in RMQ score of 4.4 points was found in those patients who said they had resumed full activities within that period. The former is the change that might be expected in the average patient with an acute, simple back problem. The latter is a response that indicates an improvement in those who got better. It can also be linked to the shift from acute low back pain to resumption of full activities for an average patient. The change score is therefore anchored in a meaningful concept. The purpose of this article is to show how studies of responsiveness can serve as a method to build up an understanding of the meaning (clinical relevance and clinical importance) of change scores in self-report measures. Examples from studies using one outcome, the RMQ are included. The RMQ was chosen because of the availability of many studies of its responsiveness.