| 1 | Rule 1: A parameter-invariant function of AVAL and BASE on the same row that does not involve a transform of BASE should be added as a new column. | The three conditions of Rule 1 for when a function of AVAL and BASE should be added as a column (i.e., a function column) are: - The function is of AVAL and, optionally, BASE, on the same row; and
- The function is parameter-invariant; and
- The function does not involve a transform of BASE.
The remainder of the discussion of this rule is devoted to explaining these conditions. PARAM uniquely describes the contents of AVAL or AVALC. Often, AVAL itself is not the value that is needed for analysis. For example, in a change from baseline analysis, it is the change from baseline CHG that is analyzed. The change from baseline column CHG should be created according to Rule 1 because it satisfies the three conditions: - CHG is derived from AVAL and BASE on the same row.
- The same calculation applies on all rows in the dataset on which CHG is populated (the function CHG=AVAL-BASE does not vary according to PARAM). This second condition is known as the property of parameter-invariance; unless listed in ADD LINK Section 3, Standard ADaM Variables, a function of AVAL (and optionally BASE) may not be derived as a column if it is parameter-variant (i.e., is calculated differently for different parameters).
- In the function CHG=AVAL-BASE, BASE is not transformed.
The intent is to use the standard columns as much as possible, to keep the structure as standard as possible, and avoid undue "horizontalization," while still permitting efficient use of function columns. |