16 Mar
2012
16 Mar
'12
10:47 a.m.
Patty the example was to show issues of aggregation not to talk about
one Block Group. The reason the Block Group using mode was used was for
my exercise was because I could identify the difference in the MOE that
was calculated using 4 and 5 variables verse 2 variables to get the same
MOE. Are there any relationships in the MOE noise that we can develop
as we aggregate variables together?
I did liked Cemal's idea of doing a stepwise approach in aggregating in
a few variable at a time. Looking at the effects of doing this could
prove interesting. If anyone has tried this please share what you have
seen or learn. I think we are all learning here.
Patty Becker wrote:
Ed,
Working with any one block group almost anywhere in the county
(Manhattan comes to mind as a possible exception) will have such high
MOEs that the data are not worth anything, must less your time! There
just are not enough interviews in a single block group of, on the
average, 300 housing units, even over five years, to produce decent
data. The only point of making BG data available is for aggregation,
especially in the radius analyses so popular in the private sector.
Patty Becker
At 08:59 AM 3/16/2012, you wrote:
--
Ed Christopher
708-283-3534 (V)
708-574-8131 (cell)
FHWA RC-TST-PLN
4749 Lincoln Mall Drive, Suite 600
Matteson, IL 60443
Mara--Let me know if you hear anything. I think
this is a very
perplexing question and worthy of some research under the banner of
"how to work with ACS data, tips and tricks".
Attached is something I did that might give you "a little" insight.
On the attached slide I had a block group table with 5 different modes
to work, the Total Population and Total Workers. What I wanted to do
was to figure out the total number of commuters along with the MOE.
Remember Census does not give us the Total Commuters with the block
group data. Doing the math to get Total Commuters was easy, just add
up the modes. However, the MOE became something of a guessing game. I
first used the formula for for calculating the MOE for more than two
estimates. I got one number 214 (with 4 variables) or 245 (with 5
variables) depending if you used the MOE associated with a cell that
had zero observations. Dealing with zero cells in ACS brings its own
issues and questions.
I then realized that the total commuters was actually the difference
between the Total Workers and those who Worked at Home, only two
variables. That allowed me to use a different MOE formula (which by
the way is the same even though I was subtracting values instead of
adding) and I got 209.
My point is that although small with only 4 variables I was
introducing some additional error by increasing the number of
variables. Exactly how much I wasn't sure. If I did not consider the
zero cell MOE influence, the added error was in the neighborhood of
2.3%. So what I found is that as you increase variables your MOE
calculation would then have an additional MOE. Hey a new statistic,
the MOE of the MOE.
What I could have done is a few more Block Groups and found some with
no zero values so that I could see what 5 variables as opposed to 4
did but that is where I think this is worthy of research by someone
with a statical mind.
mkaminowitz(a)baltometro.org wrote:
-------------------------------------------------------------------------------------------------
Patricia C. (Patty) Becker 248/354-6520
APB Associates/SEMCC FAX 248/354-6645
28300 Franklin Road Home 248/355-2428
Southfield, MI 48034 pbecker(a)umich.edu
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http://ryoko.chrispy.net/mailman/listinfo/ctpp-news 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(a)baltometro.org < mailto:mkaminowitz@baltometro.org>
www.baltometro.org <http://www.baltometro.org/>
< http://www.baltometro.org/>__
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--
Ed Christopher
708-283-3534 (V)
708-574-8131 (cell)
FHWA RC-TST-PLN
4749 Lincoln Mall Drive, Suite 600
Matteson, IL 60443
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