Date:         Wed, 11 Jun 2008 14:56:55 -0500
Reply-To:     Mary <mlhoward@avalon.net>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Mary <mlhoward@AVALON.NET>
Subject:      Re: Relative risks and risk differences in SAS?
Content-Type: text/plain; charset="iso-8859-1"

Thanks, and also to a few responses offlist. 

I did find a nice website with an example.   It is:
http://www.ats.ucla.edu/STAT/sas/faq/relative_risk.htm

Though I found that I wanted to use the reference parameter in my class statement, so I wound up with:

proc genmod data=set2 descending;

class var1(param=ref ref='0') ;

model disease=var1/dist=binomial link=log;

estimate 'Beta' var1 1 -1 /exp;

run;

-Mary

  ----- Original Message ----- 
  From: Nordlund, Dan (DSHS/RDA) 
  To: SAS-L@LISTSERV.UGA.EDU 
  Sent: Wednesday, June 11, 2008 2:34 PM
  Subject: Re: Relative risks and risk differences in SAS?


  > -----Original Message-----
  > From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On
  > Behalf Of Mary
  > Sent: Wednesday, June 11, 2008 11:04 AM
  > To: SAS-L@LISTSERV.UGA.EDU
  > Subject: Relative risks and risk differences in SAS?
  >
  > Hi,
  >
  > I just got a request for relative risks- here is is:
  >
  > Do you know if your statistics package can estimate relative risks and
  >
  > risk differences based on odds ratios and known or estimated
  >
  > population fraction of cases (prevalence)?  I was reading through a
  >
  > paper by Gary King (http://gking.harvard.edu/files/abs/1s-abs.shtml)
  >
  > and was wondering if the relative risk or risk reduction of having a
  >
  > particular SNP would be easier to understand than just p-values or
  >
  > odds ratios.
  >
  >
  >
  > I'm not familiar with this- does anyone know how this is done in SAS?
  >
  >
  >
  > -Mary
  >

  Mary,

  PROC FREQ will report relative risk if you have the counts.  You will need more than an odds ratio and prevalence to get to relative risk.  You will need the individual odds that make up the odds ratio.

  I'm not sure that relative risks are any more understandable than odds ratios (well maybe a little, but people can easily get confused with relative risks).  Relative risks can change markedly depending on whether you are looking at the probabilility of occurrence or non-occurrence.

  Here is an excellent, simple comparison of odds ratios and relative risks.

  http://www.childrensmercy.org/stats/journal/oddsratio.asp

  Hope this is somewhat helpful,

  Dan

  Daniel J. Nordlund
  Washington State Department of Social and Health Services
  Planning, Performance, and Accountability
  Research and Data Analysis Division
  Olympia, WA  98504-5204