[acs-r] divide.acs question

[Ezra Haber Glenn]

Brian:

Thanks for your email, and for using the package.

The divide.acs function implements the formulas recommended by the
Census in their "Compass" series -- see, for example, "A Compass for
Understanding and Using American Community Survey Data: What State and
Local Governments Need to Know"
(<http://www.census.gov/acs/www/Downloads/handbooks/ACSstateLocal.pdf>).  

To calculate the MOE (or standard error) for proportions, there is a
formula in the appendix (page A-14) of that guide.  As noted there:

  "There are rare instances where this formula will fail---the value
  under the square root will be negative.  If that happens, use the
  formula for derived ratios ... which will provide a conservative
  estimate of the MOE."

As far as I can tell, this is the best option -- but I would note that
if only some of your calculations trigger this issue, you may want to
be consistent as use method="ratio" for all of them.

Also, since others may be wondering about this as well, would you mind
if I posted your question (and my answer) to the acs-r user group mail
list (see <http://mailman.mit.edu/mailman/listinfo/acs-r>)...?

--Ezra

At Fri, 13 Sep 2013 15:00:21 -0400, Brian Bowling wrote:
> 
> [1  <text/plain; us-ascii (quoted-printable)>]
> 
> [2  <text/html; us-ascii (quoted-printable)>]
> Hello,
> 
> I was working my way through the acs.R presentation you did for the
> Orange County R Users Group, but I was using data for Allegheny
> County, Pa., instead of Bristol County, Wash.
> 
> When I tried to get divide.acs to use the proportion method instead of
> the ratio method, I received the following warning:
> 
> Warning message:
> 
> In .acs.divider(num = numerator, den = denominator, proportion = T, :
> 
>   ** due to the nature of some of the errors, using the more
>      conservative formula for RATIOS,
> which assumes that numerator is not a subset of denominator **
> 
> Is there any way to compel it to use the proportion method?
> 
> Regards,
> 
> Brian Bowling
> 
> Reporter
> 
> Pittsburgh Tribune-Review
> 
> triblive.com
> 
> (o) 412-325-4301
> 
> (c) 412-549-1707
> 
> 

--
Ezra Haber Glenn, AICP
Department of Urban Studies and Planning
Massachusetts Institute of Technology
77 Massachusetts Ave., Room 7-337
Cambridge, MA 02139
eglenn at mit.edu 
http://dusp.mit.edu/faculty/ezra-glenn | http://eglenn.scripts.mit.edu/citystate/
617.253.2024 (w)
617.721.7131 (c)