Cliff et al--don't be perplexed ;-) When preparing large data sets stuff
happens. Our friends at the bureau looked into Table 303100 and the
issue with subcategories not adding up to total counts. Good news! It's
not a data issue, it's a software tool issue. In the CTPP data tool,
they were able to verify the discrepancies between the totals and
subtotals observed for Cambridge. they then checked the numbers for the
original tables delivered from the Census Bureau. Those tables are
correct. That is, the subtotals add up to the totals (with typical minor
rounding discrepancies, of course). For now the assumption is that it
is just a simple instance of the table drawing from the wrong total line
in the tool. Needless to say there is some circling back to the software
folks.
On 8/14/2019 9:54 AM, Cook, Cliff wrote:
Ed
I thought you’d be interested in the following from Le Zhang from NYC DEP:
I just checked the Table B303100 state-to-state flows. The estimated
US total workers is over 232M, whereas the sum of all income brackets
is only 145M. The latter makes much more sense to me. Therefore, I
think the issue very likely has a national impact.
We continue to be perplexed by this problem. If anyone has any
suggestions for the source we are interested to learn more.
Cliff Cook
*From:*Ed Christopher <edc(a)berwyned.com>
*Sent:* Monday, August 12, 2019 1:24 PM
*To:* ctpp-news(a)chrispy.net; Cook, Cliff <ccook(a)cambridgema.gov>
*Cc:* Werner, Bailey <bwerner(a)cambridgema.gov>
*Subject:* Re: [CTPP] FW: 2012-16 CTPP Question about Counts
Cliff--The geocoding issue that was mentioned is not affecting or part
of your issue. That is a whole different issue.
As to what you are seeing in Cambridge I still do not have an answer
for the Part 3 income tables (B303100 and B303201) but I think we
could be getting close to figuring it out. I just checked the numbers
for my town which is much smaller and has no Group Quarters. That
means that I should get consistent numbers across all the Part 3
tables which I did except for the income tables. BTW, my town of
Berwyn IL has a total of 2,600 internal worker flows, people living
and working in Berwyn. Of course tables A302100 and A302103 (total
workers and worker by mode) gave me 2,595 workers but we know that
difference is due to disclosure proofing. Now on to the income table.
Typically the cells in a CTPP table will not add up to the total
because the totals are rounded independently of the cells (more
disclosure proofing). However they would never be as far off as we are
seeing. In checking my town's Part 3 income tables I discovered that
the cells added to the total number I was expecting (2,600) while the
total was published at 4,000. The question now becomes what does the
total represent? Whatever it is looks to be systematic which means we
will be able to figure it out. More digging needed though.
On 8/12/2019 11:22 AM, Cook, Cliff wrote:
Dara
Thank you for these materials. They are very helpful. After
taking a closer look at the CTPP flow tables we are still left
with a question about why the components of certain tables do not
add up to the table total. For example when we filter for
Cambridge, MA as both residence and workplace, the “Total” shown
in Table B303100 is 37,500 while the component cells add up to
22,470. This problem appears in all the part 3 tables whose
universe is household workers. (We do not see a similar issue in
all tables based purely in worker characteristics, regardless of
living arrangement. Those seem to consistently sum to 27,725.)
Can anyone shed light on why the table components to sum to the
sum stated in the table?
Thanks
Cliff Cook
*Clifford Cook
Senior Planning Information Manager*
Cambridge Community Development Department
344 Broadway, Cambridge, MA. 02139
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*From:* Dara Goldberg (DCP) <DGoldberg(a)planning.nyc.gov>
<mailto:DGoldberg@planning.nyc.gov>
*Sent:* Monday, August 12, 2019 11:13 AM
*To:* Cook, Cliff <ccook(a)cambridgema.gov>
<mailto:ccook@cambridgema.gov>
*Cc:* Werner, Bailey <bwerner(a)cambridgema.gov>
<mailto:bwerner@cambridgema.gov>; Le Zhang (DCP)
<LZHANG(a)planning.nyc.gov> <mailto:LZHANG@planning.nyc.gov>
*Subject:* RE: 2012-16 CTPP Question about Counts
Hello Cliff,
The reason the flows are off is because the CTPP methodology for
reporting geographies below the county level has been revised for
this release (though AASHTO has yet to release documentation
stating such). Missing records for smaller geographies are no
longer imputed for Parts 2 and 3, therefore, tracts/places will no
longer add to counties, nor will they have complete counts. This
has resulted in a “truer” data set, albeit with missing records.
Part 1 remains the same (i.e. “complete”), because it represents
ACS data at place of residence. I’ve attached a memo summarizing
the challenges with the new release.
My colleague Le, who I have CC’d, put together the attached
presentation explaining this issue, which we shared with our MPO
members a couple of months ago. Le will be presenting this to the
CTPP oversight board in Arkansas next week. Unfortunately, there
was no documentation released accounting for the methodological
change, and we believe transportation planners will rely on the
current release to have a “complete” count as the prior releases
had. Therefore, this release is not comparable to the prior
releases for smaller geographies.
In the meantime, we have assumed a proportional allocation to
account for missing records (though this of course introduces a
bias into the results – also covered in Le’s presentation).
Hopefully this helps! Happy to answer any questions you might have.
Regards,
DARA GOLDBERG
SENIOR PLANNER | REGIONAL PLANNING DIVISION
NYC DEPT. OF CITY PLANNING
120 BROADWAY, 31^st FLOOR• NEW YORK, NY 10271
212-720-3312 I _DGOLDBERG(a)planning.nyc.gov
<mailto:DGOLDBERG@planning.nyc.gov>_
http://www.nyc.gov/planning
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*From:* ctpp-news [mailto:ctpp-news-bounces@chrispy.net] *On
Behalf Of *Cook, Cliff
*Sent:* Monday, August 12, 2019 10:58 AM
*To:* ctpp-news(a)chrispy.net <mailto:ctpp-news@chrispy.net>
*Cc:* Werner, Bailey <bwerner(a)cambridgema.gov
<mailto:bwerner@cambridgema.gov>>
*Subject:* [CTPP] 2012-16 CTPP Question about Counts
To All
We are working to collect information about the resident labor
force in Cambridge, Massachusetts. We set the residence as the
State-Place of Cambridge city, MA, and the workplace as POW
State-Place of Cambridge city, MA.
The numbers in the CTPP Flows tables are not adding up as
expected. Table A304100 – Total workers (1) (Workers 16 years and
over) provides an estimate of _27,725_ (MOE 847), whereas Table
B303100 – Household income in the past 12 months (2016$) (9)
(Workers 16 years and over in households) provides a total
estimate of _37,300_ (MOE 2,054). Furthermore, when we add up the
count of workers in each income bracket in Table B303100 they sum
to _22,470_.
I could understand if the total number of resident workers 16 and
older in households was smaller than total workers over 16, but we
cannot make sense of how the reverse could be true. It also
doesn’t explain why the sum of all categories is smaller than the
listed total. Could data suppression account for this? That
would seem unlikely at the level of a city of our size. Could the
results be due to data suppression at smaller geographic levels
having a ripple effect on a larger geo? I understand workers with
an unclear or imprecise work address are excluded from the flow
data. Are these issues a result of that screening or is this a
different type of issue?
Interestingly, the numbers make sense as expected when we look at
the Residence tables for the same geography. Table A102101 – Total
workers (1) (Workers 16 years and over) provides an estimate of
61,925 (MOE 1,008) and Table A103100 – Total Workers in households
(1) (Workers 16 years and over in households) estimates 54,195
(MOE 1,075).
Any help on interpreting our resident labor force stats is
appreciated.
Cliff Cook
*Clifford Cook
Senior Planning Information Manager*
Cambridge Community Development Department
344 Broadway, Cambridge, MA. 02139
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