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As illustrated in the study schema diagram for Example Trial 1, this simple parallel trial has 3 arms, corresponding to the 3 possible left-to-right "paths" through the trial. Each path corresponds to 1 of the 3 elements at the right end of the diagram. Randomization is represented by the 3 red arrows leading from the Run-in block.
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The next diagram for this trial shows the 3 epochs of the trial, indicates the 3 arms, and shows the sequence of elements for each group of subjects in each epoch. The arrows are at the right side of the diagram because it is at the end of the trial that all the separate paths through the trial can be seen. Note that, in this diagram, randomization—which was shown using 3 red arrows connecting the Run-in block with the 3 treatment blocks in the first diagram—is indicated by a note with an arrow pointing to the line between 2 epochs.
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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. Later examples will illustrate that this is not always the case.
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| Screen | Run-in | Study Product Testing | Follow-Up | |
|---|---|---|---|---|
| Placebo | Screen | Run-in | PLACEBOUsual Tobacco Product | Follow-Up |
| A | Screen | Run-in | DRUG Tobacco Product A | Follow-Up |
| B | Screen | Run-in | DRUG Tobacco Product B | Follow-Up |
For Example Trial 1, the conversion of the trial design matrix into the TA dataset is straightforward. For each cell of the matrix, there is a record in the TA dataset. ARM, EPOCH, and ELEMENT can be populated directly from the matrix. TAETORD acts as a sequence number for the elements within an arm, so it can be populated by counting across the cells in the matrix. The randomization information, which is not represented in the trial design matrix, is held in TABRANCH in the TA dataset. TABRANCH is populated only if there is a branch at the end of an element for the arm. When TABRANCH is populated, it describes how the decision at the branch point would result in a subject being in this arm.
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