## In SAS, how can I calculate age from the date-of-birth data?

In SAS, date type variables contain the number of days between January 1, 1960, and the date specified. To compute age using a date of birth and the current date, use the following code:

DATA birth; INPUT id birthday MMDDYY6.; today = DATE(); days = today - birthday; age = floor(days / 365); DATALINES; 01 122275 02 010865 03 030586 . . RUN;

The input format MMDDYY6. specifies month, day, and year in six digits. You can also use other formats, such as MMDDYY8. (e.g., 12/31/68, 12-31-68, 12.31.68, or 12311968), DDMMYY6., and DDMMYY8..

DATE() returns the current date set in the computer. To specify a particular day, use the MDY() function as follows:

today = MDY(03,31,2008);

The floor function takes the integer part of age for colloquial usage, but does not take into account the effect of leap years. To avoid this problem, use the intck function by replacing age = floor(days / 365); in the above code with:

age = floor ((intck('month',birthday,today) - (day(today) < day(birthday))) / 12);

The intck function will correct for leap years. The first part of the command, intck('month',birthday,today), returns the number of times the first day of a month is passed between birthday and today. To correct for the number of times the same day of the starting month has passed, the logical test (day(today) < day(birthday)) is used, resulting in a value of 0 or 1 to be subtracted from the initial calculation of months. Finally, the corrected number of months is divided by 12 and rounded to produce the correct age.

If you have questions about using statistical and mathematical software at Indiana University, email UITS Research Analytics (formerly known as the Stat/Math Center). Research Analytics is located on the IU Bloomington campus at Woodburn Hall 200, and is open for consultation by appointment Monday-Friday 9am-5pm. For more, visit Research Analytics on the web, or call 812-855-4724 (IUB) or 317-278-4740 (IUPUI).

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