Date: Tue, 30 Apr 2002 08:55:40 0500
ReplyTo: Knada <knada@ACESAG.AUBURN.EDU>
Sender: "SAS(r) Discussion" <SASL@LISTSERV.UGA.EDU>
From: Knada <knada@ACESAG.AUBURN.EDU>
Organization: Auburn University
Subject: Re: Age calculation in epidemiology
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Dietrich Alte wrote:
>
> Dear all,
>
> we have run into a controversy how to calculate probands' age and
> derive age groups in our epidemiological study.
>
> option 1)
> 
> Take the difference in days between day of birth and day of
> examination and divide this by 365.25 (or 365.24) and round the result
> to full years, e.g. 45.5000 to 46 and 45.4999 to 45. This will yield
> full year "age estimates" that are nearest to the true value.
>
> option 2) (everyday approach)
> 
> Count the number of completed years between day of birth and day of
> examination, as one would do in every day conversations, e.g. if the
> examination is at May 23, 2001 and somebody was born May 23, 1950,
> then he is 51, if the examination was at May 22, 2001, then he is 50
> at examination. This will yield the "every day approach" age in full
> years, but will on average be 0.5 yrs too low compared to the real
> nonrounded value.
>
> If we then compute age ranges like 20  < 30, we get different
> numbers from these 2 options.
>
> Which one is normally used in publications, when statistics grouped
> bei 5yr or 10yr ranges are to be given?
>
> (If requested I will send a summary of replies to the list.)
>
> Thanks in advance for answering.
>
> 
> 
> Dietrich Alte (Statistician, Dipl.Stat.)
> University of Greifswald  Medical Faculty
> Institute of Epidemiology and Social Medicine
> WaltherRathenauStr. 48, D17487 Greifswald, Germany
> Phone +49 (0) 3834  86 77 13, fax +49 (0) 3834  86 66 84
> Email alte@mail.unigreifswald.de
> Institute http://www.medizin.unigreifswald.de/epidem/
> Study http://www.medizin.unigreifswald.de/epidem/ship.htm
> 
Hello Dietrich:
As I see from your posting at the end you are simply computing age
groups of ranges of 10yrs (20  < 30 yrs) so why bother about the Age
Estimates nearest to the TRUE value?. You can very well compute the best
estimates of age groups range from your first option for the same group
(eg: 20  < 30 yrs) as :
Age group 1: < 10.4999;
Age group 2: > 10.4999 and < 20.4999;
Age group 3: > 20.4999 and < 30.4999;
...
and ..... so on.
That will reflect your true Age Groups estimates.
Some thoughts.

*****************************************
* Nada K. Nadarajah, PhD *
* Research Associate *
* Dept. Animal and Dairy Science *
* 214 Upchurch Hall *
* Auburn University, AL 368495415 *
* USA *
* Tel:3348441502 Fax: 3348441519 *
* email knada@acesag.auburn.edu *
* *
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