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The next diagram can be thought of as the retrospective view of a trial, the view back from a point in time when a subject’s assignment to an arm is known. In this view, the trial appears as a grid, with an arm represented by a series of study cells, one for each epoch, and a sequence of elements within each study cell. In this example (as in many trials), there is exactly 1 element in each study cell. In more complicated designs this is not always the case.

The next diagram shows the trial from the viewpoint of blinded participants. To blinded participants in this trial, all arms look alike. They know when a subject is in the screen element or the run-in element, but when a subject is in the treatment epoch, participants know only that the subject is receiving a study drug, not which study drug, and therefore not which element. 

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