The efficacy of warfarin for the prevention of stroke in nonvalvular atrial fibrillation: Measuring its minimal clinically important difference from the patients' perspective.

Objectives. (1) To develop a probability trade-off technique (PTOT) for determining the minimal clinically important difference (MCID) of warfarin therapy from the patients' perspective; (2) to estimate the MCID for the efficacy of warfarin to prevent stroke in the treatment of nonvalvular atrial fibrillation (NVAF) from the perspective of patients with this disease and who have experienced a course of warfarin therapy; (3) to assess two different methods of eliciting the patients' MCID. The two elicitation methods were: (1) ping-ponging (PP), in which the hypothetical efficacy of warfarin to prevent stroke was varied from one extreme to the other until the patients' MCID was determined; and (2) starting at known efficacy (SKE), in which the hypothetical efficacy was started at a midpoint value and then incrementally increased or decreased until the patients' MCID was determined. Conclusions. The MCID for this group of patients was much smaller than the known efficacy of warfarin to prevent stroke in patients with NVAF. The PTOT, using the flipchart approach, was well accepted and appeared to improve their knowledge of their disease, and its consequences and treatment. The method of elicitation used to determine the patients' MCIDs can have a clinically important effect on their responses. (Abstract shortened by UMI.