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The next diagram for this crossover trial shows the prospective view of the trial; it identifies the epoch and arms of the trial, and gives each a name. As for most crossover studies, the objectives of the trial will be addressed by comparisons between the arms and by within-subject comparisons between study product exposures. Because the design depends on differentiating the periods during which the subject receives the 3 different study product exposures, there are 3 different study product exposure epochs. The fact that the rest periods are identified as separate epochs suggests that these also play an important part in the design of the trial; they are probably designed to allow subjects to return to “baseline,” with data collected to show that this occurred. Note that epochs are not considered reusable; each epoch has a different name, even though all the study product exposure epochs are similar and both the rest epochs are similar. As with the first example trial, there is a one-to-one relationship between the epochs of the trial and the elements in each arm.

The next diagram shows the retrospective view of the trial.

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