Overview
On the Variable Finder tab in Data Sets Calculated Variables and in Filters there is a column labeled Interval. Universal and Project variables are not associated with an interval thus for those variables the column is blank. Encounter variables will be listed with each variable at each interval where it is collected. In Calculated Variables, the encounter variables will also be listed with an interval of Data Set Intervals.
Using the Interval Value
When creating a filter you select the interval by which to filter the variable's value. If filtering for a variable at all intervals, then each instance of the variable is selected.
Example:
To create a filter that only includes subject's whose weight exceeds 200 lbs at any encounter:
- On the Variable Finder tab, select the variable Weight at each interval. Thus, if weight is collected at 3 encounters there will be 3 variables that need to be added.
- On the Attributes tab, the variables will be assigned aliases of V1, V2, and V3
- The Filter would be: V1>200 OR V2>200 OR V3>200
When creating a calculated variable, selecting Data Set Intervals will execute the calculation at each interval that is specified on the Intervals tab of the Data Set. If a calculation uses a value at a specific interval only then the variable for that interval would be selected.
Example:
To create a calculated variable that calculates a subject's increase in weight from Baseline to each encounter:
- On the Variable Finder tab, select the variable Weight at Baseline (alias V1 assigned by StudyTRAX)
- Select the variable Weight at Data Set Intervals (alias V2 assigned by StudyTRAX)
- On the Expression tab, the Expression would be: V2-V1