Defining Change
Abstract
"Change comes like a little wind that ruffles the curtains at dawn, and it comes like the stealthy perfume of wild- flowers hidden in the grass." --John Steinbeck, Sweet Thursday The ability to recognize change, whether improvement or deterioration, in a patient's health is a vital part of clinical medicine. In studies that report the results of medical or surgical treatment, it is important not only to recognize change but to be able to quantify and communicate the magnitude of that change to readers. A contemporary way to measure change in health status is by comparing scores obtained with a standardized out- comes instrument before and after a given intervention. In psychometric jargon, the arithmetical difference between the 2 scores is known as the change score. If an outcomes instrument is responsive, a patient's score should change whenever his or her health status changes, and the amount of change should be reflected in the magnitude of the change score. As Steinbeck implies, however, change can be a subtle phenomenon. Psychometrically, it can be defined in a number of ways.1 "Responsiveness of the International Knee Documentation Committee Subjective Knee Form" by Irrgang et al focuses exclusively on the ability