MARK Subcommand (CASEPLOT command)

Use MARK to indicate the onset of an intervention variable.

• The onset date is indicated by a horizontal reference line.
• The specification on MARK can be either a variable name or an onset date if the DATE_ variable exists.
• If a variable is named, the reference line indicates where the values of that variable change.
• A date specification follows the same format as the DATE command—that is, a keyword followed by a value. For example, the specification for June, 1955, is Y 1955 M 6 (or Y 55 M 6 if only the last two digits of the year are used on DATE).

Figure 1. MARK Y=1990