Date:         Tue, 24 May 2005 13:23:54 -0400
Reply-To:     "Sridhar, Kumar" <nsridhar@MEDAREX.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "Sridhar, Kumar" <nsridhar@MEDAREX.COM>
Subject:      Re: Question on Proc SQL - correct age formula
Comments: To: "Choate, Paul@DDS" <pchoate@DDS.CA.GOV>
Content-Type: text/plain; charset="us-ascii"

You wrote < It handles all birthdates precisely except Jan 29, which is
close but not perfect.>

Would I be right in presuming that you meant Feb.29?

Regards

Kumar

-----Original Message-----
From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On Behalf Of
Choate, Paul@DDS
Sent: Tuesday, May 24, 2005 1:03 PM
To: SAS-L@LISTSERV.UGA.EDU
Subject: Re: Question on Proc SQL - correct age formula

Hi Kevin & Kumar -

YRDIF is close, but not perfect.  Since the 366 vs 365 divisor is
relative
to the person's birthdate, not Jan 1, YRDIF still has a small error
associated with it.

Wialliam Kreuter has provided a correct formula:

age = floor
((intck('month',birth,somedate)
- (day(somedate) < day(birth))) / 12);

or the macro:

%macro age(date,birth);
floor ((intck('month',&birth,&date)
- (day(&date) < day(&birth))) / 12)
%mend age;

(http://ftp.sas.com/techsup/download/sascomm/sascom-tt-4q98a.html)

It handles all birthdates precisely except Jan 29, which is close but
not
perfect.

Look around here:

SAS.COM
http://search.sas.com/suppquery.html?col=suppsas&qt=Kreuter

SAS-L
http://xrl.us/f7ou

regards

Paul Choate
DDS Data Extraction
(916) 654-2160

-----Original Message-----
From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On Behalf Of
Kevin
Roland Viel
Sent: Tuesday, May 24, 2005 7:53 AM
To: SAS-L@LISTSERV.UGA.EDU
Subject: Re: Question on Proc SQL

> But I have a question in regards to the difference
> (and it maybe a nave question) but would you know why the difference
> occurs?

Our concept of years of age typically mean the number of times something
reach the month and day of its birth in the cycle of years.  The
discrepancy results from the integer representation of an approximation.

Some years have 366 days and some have 365.  Since (approximately) every
four years has 366, we say that, on average, a year is 365.25.  Not
every
fourth year has 366, for instance 1900.

The YRDIF() function, will correctly divide by 366 or 365 as
appropriate.

Regards,

Kevin



Kevin Viel
Department of Epidemiology
Rollins School of Public Health
Emory University
Atlanta, GA 30322