topic Re: RE: Calculation person-year. in SAS Programming

RE: Calculation person-year.

PhanS — Tue, 23 Oct 2012 15:49:15 GMT

Hello everyone,

I am seeking SAS syntax for 'calculation person-year'. I am interested in looking an incidence rate of first stopping ARV in HIV populations.

I much appreciate anyone helps me with this concept.

Thanks in advance.

Re: RE: Calculation person-year.

art297 — Tue, 23 Oct 2012 16:41:48 GMT

Couldn't you use the yrdif function (with the age option) to achieve what you want? Take a look at:

http://support.sas.com/documentation/cdl/en/lefunctionsref/63354/HTML/default/viewer.htm#p1pmmr2dtec32an1vbsqmm3abil5.htm

Re: RE: Calculation person-year.

Reeza — Tue, 23 Oct 2012 16:46:53 GMT

I think the OP is looking for the epidemiological aspect of person-year, which usually means changing your data structure. But it depends on what format the data is in and what question you're asking.

http://meds.queensu.ca/medicine/obgyn/pdf/what_is/What.is.person-time.pdf

AFAIK There isn't a PROC that can do that for you, you'll need to write your own datastep to solve it.

Re: RE: Calculation person-year.

Doc_Duke — Tue, 23 Oct 2012 17:35:01 GMT

To follow up on Reeza and Art, the person-year of exposure to ARV would be the difference between the start of ARV and the first stopping (you can do with with yrdif or the approximate formula "(stopdate-startdate)/365.25". To get the overall person-years of exposure, use PROC SUMMARY and get the sum.

Doc Muhlbaier

Duke

Re: RE: Calculation person-year.

PhanS — Tue, 23 Oct 2012 17:37:56 GMT

Hello,

I do have the Eric document. I helps to understand the concept of person-year. I do agree with you that I have to write code my myself. At the meantime, I don't think I have never seen an example or taught about SAS syntax to apply for person-time.

It would be very helpful if any SAS experts can built an example for this issue for SAS users.

Thanks.

Phan

Re: RE: Calculation person-year.

Doc_Duke — Tue, 23 Oct 2012 17:42:33 GMT

Try this Google search, you'll see lots of examples

person-year calculation site:sas.com

Re: RE: Calculation person-year.

PhanS — Tue, 23 Oct 2012 17:45:40 GMT

Dear Art,

I am not sure the 'calculation person-age' is similar to 'person-year' that Reeza has mentioned. He provides a useful document about the concept of 'person-year'.

I am trying to build SAS codes and I would like to share if I achieved.

Thanks,

Phan

Re: RE: Calculation person-year.

PhanS — Tue, 23 Oct 2012 17:48:03 GMT

Hello,

Thanks for your contribution. I will follow-up later.

Thanks

Phan

Re: RE: Calculation person-year.

art297 — Tue, 23 Oct 2012 17:53:17 GMT

Phan,

I've never worked in the area of epidemiological research, thus am not aware of the various nuances described in the reference that Fareeza provided. However, I'd be interested in knowing why a calculation similar to the calculation of age wouldn't be relevant.

The following mimics one of the examples from that reference:

Time contributed by each subject:

Subject A: 2.5 years

Subject B: 5 years

Subject C: 1.5 years

Subject 😧 5 years

Subject E: 0.5 years

data have;

informat initial_date onset_date date9.;

format initial_date onset_date date9.;

input subject $ initial_date onset_date;

person_years=yrdif(initial_date, onset_date, 'AGE');

cards;

A 01JAN2007 01JUL2009

B 01JAN2005 01JAN2010

C 01JAN2010 01JUL2011

D 01JUN2007 01JUN2012

E 01JUN2011 01DEC2011

;

: is that different from what the OP is seeking?

Re: RE: Calculation person-year.

Reeza — Tue, 23 Oct 2012 18:05:07 GMT

That will give you the person-years per person, but then you need the proc summary as suggested by doc@duke.

I'm a She not a He

Re: RE: Calculation person-year.

PhanS — Tue, 23 Oct 2012 19:05:51 GMT

Dear Reeza,

My sincere apologies as I have difficulties with names. I appreciate and thank for your telling me.

Re. your advice, I will test later tonight and will follow-up.

Phan

Re: RE: Calculation person-year.

PhanS — Tue, 23 Oct 2012 19:08:22 GMT

Dear Art,

Many thanks for your follow-up. Through Reeze's comments, it appears that you are logic.

I may not have time to run a test at this moment, but will do tonight. I am happy to inform you.

Thanks,

Phan

Re: RE: Calculation person-year.

PhanS — Wed, 24 Oct 2012 21:36:13 GMT

Dear Everyone,

My sincere apology that I couldn't get back last night.

To Art, I tested the yrdif (as well as dtdif) using methods/instructions from SAS Helps, unfortunately I had a message from log file: character values have been converted to numeric values at the places given by ...

I am not sure what is wrong with the code.

Greatly, I used the approximate formula (doc@duke), it appears to be fine for my results.

As Reeze's comment, however, I need to develop several step fro proc summary, proc freq and proc mean to calculate 'sum' of variable that I need.

Overall, I think to calculate person-year is required several steps. These steps are very helpful for new SAS users like me.

One thing that I have no idea for Art is the code does not work. If possible, I will see a stat person in my place if he can help me to identify the erros.

At the meantime, I much appreciate and want to thank everyone in helping me this procedure. Again thanks.

Phan S.

Re: RE: Calculation person-year.

art297 — Wed, 24 Oct 2012 22:39:29 GMT

Phan,

I failed to mention that the code I suggested requires SAS 9.3. I presume you are on an older version.

Re: RE: Calculation person-year.

PhanS — Wed, 24 Oct 2012 23:21:30 GMT

Dear Art,

Thanks for the follow-up. Indeed, I am working on 9.3.

In fact, this message from log file: character values have been converted to numeric values at the places given by ... referred for another (I'm sorry to confuse you).

Lately, I will send you a log file that may help you to understand the issue when I ran the code.

I am in Vancouver, a bit inconvenience at my workplace for Internet.

Phan

Re: RE: Calculation person-year.

art297 — Wed, 24 Oct 2012 23:49:25 GMT

Not a problem. I'm in Toronto thus at least your response won't have to go through Customs.

Re: RE: Calculation person-year.

PhanS — Thu, 25 Oct 2012 00:37:07 GMT

Dear Art,

Please kindly see the log. I will see a stat person tomorrow morning and will fu you.

8617 /*person-year*/

8618 py_dead1=yrdif(farvdt, death_date, 'act/act');

8619 py_dead2=datdif(farvdt, death_date, 'act/act');

8620

8621

8626 run;

NOTE: Invalid argument to function YRDIF at line 8618 column 10.

NOTE: Invalid argument to function DATDIF at line 8619 column 10.

Thanks,

Phan

Re: RE: Calculation person-year.

art297 — Thu, 25 Oct 2012 14:43:31 GMT

Are both farvdt and death_date SAS date fields? All three of the following work for me:

data have;

informat farvdt death_date date9.;

input farvdt death_date;

/*person-year*/

py_dead1=yrdif(farvdt, death_date, 'act/act');

py_dead2=datdif(farvdt, death_date, 'act/act');

py_dead3=yrdif(farvdt, death_date, 'age');

cards;

1jan2010 10may2012

10jun2011 25oct2012

;

Re: RE: Calculation person-year.

Linlin — Thu, 25 Oct 2012 14:56:51 GMT

Hi Reeza,

I didn't know either!:smileysilly: Together we are going to change the belief "over the years, males
have dominated the SAS guru level (quoted from Art)". :smileysilly:

Re: RE: Calculation person-year.

PhanS — Thu, 25 Oct 2012 15:32:49 GMT

Dear Art, good morning!

Pls. kindly see the date SAS. I will fu with you late today, I hope to show the issue to my colleague. Thanks.

Phan

DEATH_

Obs ID FARVDT DATE

16 310 01MAR2010 .

17 340 28APR2008 .

18 350 22NOV2006 27MAR2008

19 360 23FEB2004 .

20 370 07OCT2009 .