[Application of 'stepped-wedge design' methodology in randomized controlled trials].

In this article, two research cases are employed to show the rationale of the stepped-wedge design, under what situations that such a design is desirable, and how it can be implemented. Stepped-wedge design seems to suit to randomized controlled trials in which the entire study population will receive intervention programs as they would provide more advantages than harm. When intervention can not be given to all the targets simultaneously due to limited resources, this design is particularly useful. The stepped-wedge design is also relevant when there is a hope to detect or control the time trend effect on the effectiveness of the intervention strategy. On the other hand, however, this design requires longer trial duration and presents a number of statistical challenges. Hence, careful planning and monitoring are essential to ensure that a robust evaluation is undertaken. Key words: Stepped-wedge design;  Randomized controlled trials;  Designed delay;  Staged/ phased introduction;  Phased implementation