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Each row in the TE dataset may be thought of as representing a "unique element" in the same sense of "unique" as a CRF template page for a collecting certain type of data referred to as "unique page." For instance, a CRF might be described as containing 87 pages, but only 23 unique pages. By analogy, the trial design matrix in Example Trial 1, Parallel Design Retrospective View  has 12 study cells, each of which contains 1 element, but the same trial design matrix contains only 5 6 unique elements, so the TE dataset for that trial has only 5 6 records.

An element is a building block for creating study cells, and an arm is composed of study cells. Or, from another point of view, an arm is composed of elements; that is, the trial design assigns subjects to arms, which comprise a sequence of steps called elements.

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