Hi Mara,
Each item that you aggregate will introduce
some level of uncertainty since the exact distribution of aggregated data
is not available to you. We can only estimate the aggregated MOE assuming
that each item has similar statistical distributions.
Since MOE is a function of variance,
depending on how much variance there is in your data, aggregation may produce
a confidence interval which can be reasonable or too large to be useful.
You need to evaluate the reasonableness of the aggregated MOE estimates
and associated confidence intervals. One possible way to start is to aggregate
a smaller number of counties (two or three), add a new one each time,
and track the changes in the MOE estimate.
The following reference has information
on how to work with MOEs. I also added a couple of other links I
find useful.
http://www.census.gov/acs/www/Downloads/handbooks/ACSGeneralHandbook.pdf
http://www.census.gov/acs/www/guidance_for_data_users/handbooks/
http://www.census.gov/acs/www/methodology/methodology_main/
Hope this helps.
Best of luck.
Cemal.
Cemal Ayvalik, PhD.
Cambridge Systematics, Inc.
115 South LaSalle Street, Suite 2200
Chicago, IL 60603
tel : 312 665 0209
fax: 312 346 9908
e-mail: cayvalik@camsys.com
www.camsys.com
From:
<mkaminowitz@baltometro.org>
To:
<ctpp-news@chrispy.net>
Date:
03/15/2012 11:42 AM
Subject:
[CTPP] aggregated
MOE for 6 counties
Sent by:
ctpp-news-bounces@chrispy.net
Hello,
I need to get a regional estimate and MOE
composed of 6 counties. I know the rule of thumb is that aggregating MOE's
doesn't work well for more than 4 units. Does anyone know is using 6 would
cause the MOE to be inaccurate?
Mara Kaminowitz
GIS Analyst
.........................................................................
Baltimore Metropolitan Council
Offices at McHenry Row
1500 Whetstone Way
Suite 300
Baltimore, MD 21230
410-732-0500 ext. 1030
mkaminowitz@baltometro.org
www.baltometro.org
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