Voluntariness in clinical research at the end of life.

Voluntariness is a requirement that is frequently voiced in research ethics but is poorly understood. This article seeks to clarify voluntariness and assess its significance in clinical research at the end of life. First, what voluntariness is and why we consider it important is considered. Next, where voluntariness fits in the overall context of making clinical research ethical is clarified. Finally, the murky terms "vulnerability," "exploitation," and "coercion" are clarified and their relationship to voluntariness examined. The danger of using some of these terms is that they carry a lot of moral weight and labeling patients as "vulnerable" or "coerced" can close off conversation because they are reflexively associated with unethical research. Finally, correctly characterized threats to voluntariness are examined and ways to ameliorate them are presented.