Assessing depression in systemic lupus erythematosus: determining reliable change.

Systemic lupus erythematosus (SLE) can follow an unpredictable course. Clinicians and researchers use various self-report inventories to track aspects of the patient's functioning during the course of the illness (e.g. health status, pain, fatigue, quality of life and psychological status). These self-report inventories are used to measure improvement or deterioration as a function of the natural history of the disease process, or as a function of response to treatment. Proper interpretation of scores derived from these inventories requires an understanding of their psychometric properties, in particular, their reliability. It is important to calculate reliable change difference scores for tests commonly used in rheumatology so clinicians can determine if a change score is a reliable indicator of improvement or deterioration in individual patients (i.e. the change score is not likely to be due to measurement error). The purpose of this article is to illustrate the use of the reliable change difference scores when assessing depression in patients with SLE using the Beck Depression Inventory (BDI).