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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:

1. The function is of AVAL and, optionally, BASE, on the same row; and
2. The function is parameter-invariant; and
3. 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:

1. CHG is derived from AVAL and BASE on the same row.
2. 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).
3. 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.

• If the intention is to redefine AVAL, BASE, CHG, etc. in terms of a transform of AVAL, then a new parameter must be added in which PARAM describes the transform. The creation of a new parameter results, by definition, in the creation of a new set of rows.
• For example, as described in the discussion of Rule 1, in a change from baseline analysis of the logarithm of weight, AVAL should contain the log of weight, BASE should contain the baseline value of the log of weight, and CHG should contain the difference between the two. PARAM should contain a description of the transformed data contained in AVAL, e.g., "Log10 (Weight (kg))". In this way the ADaM standard accommodates an analysis of transformed data in the standard columns without creating a multiplicity of new special-purpose columns.
• A related application of Rule 2 is in the case where it is necessary to support analysis and reporting in two different systems of units. In SDTM Findings domains such as LB, QS, EG, and so on, the --STRESN column is the only numeric result column, and is also the only standardized numeric result column. The --ORRES column contains a character representation of the collected result, in the collected units specified in the --ORRESU column. The --ORRES column is not standardized. So for example, if data are typically collected in conventional units, SDTM cannot accommodate standardized data in both conventional units and the International System of Units (SI). In SDTM, for any given --TEST, a producer can standardize in one system of units but not two. If one wishes to be able to analyze standardized results in both conventional units and in SI units, a transform in an ADaM dataset is needed. In each such case, a new parameter must be created in order to accommodate standardized data in the other system of units.
• The description in the PARAM column must contain the units, as well as any other information such as location and specimen type that is needed to ensure that PARAM uniquely describes what is in AVAL, and differentiates between parameters as needed. PARAM cannot be the same for different units.
• When a record is derived from a single record in the dataset, retain on the derived record any variable values from the original record that do not change and that make sense in the context of the new record (e.g., --SEQ, VISIT, VISITNUM, --TPT, covariates, etc.).