The Wennberg design is one of a number of variations of the randomized controlled trial (RCT), in which participants' preferences whether to receive [Page 1624]the new treatment or the comparison treatment are taken into account. The primary purpose is to minimize refusals at the recruitment stage because of the reluctance of some participants to be randomized. It might also, however, increase compliance with the intervention and improve retention rates (reduce attrition) over time as patients are receiving their preferred treatment modality.
Many procedures used in clinical research, such as random allocation, blinding of participants and raters, matching, stratification, and so forth, are done with one goal in mind—to reduce bias. In this context, bias means any systematic, nonrandom effect other than the intervention ...
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