topic Re: YRDIF oddity in SAS Programming

YRDIF oddity

deleted_user — Wed, 03 Nov 2010 17:39:58 GMT

YRDIF seems to be returning inexact results for me.

If I run the following in a data step:
test1 = yrdif('07JAN2000'd,'07JAN2001'd,"ACT/ACT");
test2 = yrdif('06JAN2000'd,'07JAN2001'd,"ACT/ACT");
test3 = yrdif('08JAN2000'd,'07JAN2001'd,"ACT/ACT");
test4 = 365/365;
and then do a Proc Freq on the results, I get:
Test1=1.0000449135
Test2=1.002777154
Test3=.9973126731
Test4=1

Test2 and Test3 are very close to what I'd expect (within floating point constraints) but I'd expect Test1 to be exactly 1. So what am I doing wrong?

Jeff

Re: YRDIF oddity

Peter_C — Wed, 03 Nov 2010 17:43:38 GMT

see usage note http://support.sas.com/kb/36/977.html

Re: YRDIF oddity

deleted_user — Wed, 03 Nov 2010 18:22:49 GMT

Well, that explains it! Thanks!

Jeff

Re: YRDIF oddity

ArtC — Wed, 10 Nov 2010 18:08:09 GMT

When the period includes a leap day, YRDIF adds the leap day and then averages it across four years (third arg is 'actual' or 'act/act'). If you are estimating a span of years then the value is off by a fraction of a day. This seems to be incrementally better than the (stop-start)/365.25 formula. Incrementally because either way the differences tend to be in the third decimal place.