Many types of clinical, patient related, and economic outcomes can be measured in trials. The choice of one or more outcomes will depend on the nature of the study and the question it is trying to answer. Objectives can relate to different levels of observation and analysis,from the individual to the family, the community, and society as a whole.

If a trial is “explanatory”1then a single main measure of clinical outcome may be appropriate. For example, if a trial is designed to determine which of two antihypertensive agents is more effective at lowering blood pressure then hypertensive control will be the main outcome. Traditionally, clinical trials have used physiological or biomedical outcomes, but these may not be well related …