[CTPP] FW: 2012-16 CTPP Question about Counts - CTPP

12 Aug 2019

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>
Sent: Monday, August 12, 2019 11:13 AM
To: Cook, Cliff <ccook(a)cambridgema.gov>
Cc: Werner, Bailey <bwerner(a)cambridgema.gov>; Le Zhang (DCP)
<LZHANG(a)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, 31st FLOOR * NEW YORK, NY 10271
212-720-3312 I DGOLDBERG(a)planning.nyc.gov<mailto:DGOLDBERG(a)planning.nyc.gov>

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From: ctpp-news [mailto:ctpp-news-bounces(a)chrispy.net] On Behalf Of Cook, Cliff
Sent: Monday, August 12, 2019 10:58 AM
To: ctpp-news(a)chrispy.net<mailto:ctpp-news(a)chrispy.net>
Cc: Werner, Bailey
<bwerner(a)cambridgema.gov<mailto:bwerner(a)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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