Multipliers and shift indexes can be used with the basic interval names to construct more complex interval specifications. The general form of an interval name is as follows:

NAMEn.s

The three parts of the interval name are shown below:

NAME

the name of the basic interval type. For example, YEAR specifies yearly intervals.

n

an optional multiplier that specifies that the interval is a multiple of the period of the basic interval type. For example, the interval YEAR2 consists of two-year, or biennial, periods.

s

an optional starting subperiod index that specifies that the intervals are shifted to later starting points. For example, YEAR.3 specifies yearly periods shifted to start on the first of March of each calendar year and to end in February of the following year.

Both the multiplier n and the shift index s are optional and default to 1. For example, YEAR, YEAR1, YEAR.1, and YEAR1.1 are all equivalent ways of specifying ordinary calendar years.

To test for a valid interval specification, use the INTTEST function:

   interval = 'MONTH3.2';
   valid = INTTEST( interval );
   valid = INTTEST( 'YEAR4');

INTTEST returns a value of 0 if the argument is not a valid interval specification and 1 if the argument is a valid interval specification. The INTTEST function can also be used in a DATA step to test an interval before calling an interval function:

   valid = INTTEST( interval );
   if ( valid = 1 ) then do;
       end = INTNX( interval, date, 0, 'E' );
   end;

For more information about the INTTEST function, see SAS Language Reference: Dictionary.