Alignment of Intervals

Date Intervals, Formats, and Functions

Alignment of Intervals

Intervals that represent divisions of a year are aligned with the start of the year (January). MONTH2 periods begin with odd-numbered months (January, March, May, and so on). Likewise, intervals that represent divisions of a day are aligned with the start of the day (midnight). Thus, HOUR8.7 intervals divide the day into the periods 06:00 to 14:00, 14:00 to 22:00, and 22:00 to 06:00.

Intervals that do not nest within years or days are aligned relative to the SAS date or datetime value 0. The arbitrary reference time of midnight on January 1, 1960, is used as the origin for nonshifted intervals, and shifted intervals are defined relative to that reference point. For example, MONTH13 defines the intervals January 1, 1960, February 1, 1961, March 1, 1962, and so forth, and the intervals December 1, 1959, November 1, 1958, and so on before the base date January 1, 1960.

Similarly, WEEK2 interval beginning days are aligned relative to the Sunday of the week of January 1, 1960. The interval specification WEEK6.13 defines six-week periods starting on second Fridays, and the convention of alignment relative to the period containing January 1, 1960 tells where to start counting to find out what dates correspond to the second Fridays of six-week intervals.

See the section "Alignment of SAS Dates" later in this chapter.

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