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The following diagram for a crossover trial study does not use the crossing slanted lines sometimes used to represent crossover trialsstudies, because the order of the blocks is sufficient to represent the design of the trialstudy. Slanted lines are used only to represent the branch point at randomization, when a subject is assigned to a sequence of study product exposures. As in most crossover trialsstudies, the arms are distinguished by the order of study product exposures, with the same study product exposure present in each arm. Note that even though all 3 arms of this trial study end with the same block (i.e., the block for the follow-up element), the diagram does not show the arms converging into one block. Also note that the same block (the "rest" element) occurs twice within each arm. Elements are conceived of as "reusable" and can appear in more than 1 arm, in more than 1 epoch, and more than once in an arm.

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The next diagram for this crossover trial study shows the prospective view of the trialstudy; it identifies the epoch and arms of the trialstudy, and gives each a name. As for most crossover studies, the objectives of the trial study 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 trialstudy; 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 trialstudy, there is a one-to-one relationship between the epochs of the trial study and the elements in each arm.

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The next diagram shows the retrospective view of the trialstudy.

The last diagram for this trial study shows the trial study from the viewpoint of blinded participants. As in the simple parallel trial study in Example Trial Study 1, blinded participants see only 1 sequence of elements; during the product exposure epochs they do not know which of the product exposure elements a subject is in.

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The following table illustrates the trial study design matrix for this crossover example trialstudy. It corresponds closely to the preceding retrospective diagram.

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It is straightforward to produce the TA dataset for this crossover trial study from the diagram showing arms and epochs, or from the trial design matrix.