Thanks for the information. I am unsure about one you thing you wrote "If you look
at the first letter of the table number "A" in not perturbated and "B"
is not" Did you mean to say that tables ending in B ARE perturbated?
From: Ed Christopher <edc(a)berwyned.com>
Sent: Monday, August 12, 2019 12:57 PM
To: ctpp-news(a)chrispy.net; Cook, Cliff <ccook(a)cambridgema.gov>
Cc: Werner, Bailey <bwerner(a)cambridgema.gov>
Subject: Re: [CTPP] 2012-16 CTPP Question about Counts
Cliff--let me take a shot at this. Between the ACS and CTPP concepts there are a lot
subtleties and a lot going on.
1. First you are working with Part 3 or Flow tables. Some of which have perturbation
applied to them and some that do not. Perturbation is what allows the CTPP to meet all the
DRB requirements. Although perturbed and non perturbed tables are mutually exclusive so
you will never have the same table, one with disclosure and one with out. However, that
does not explain your difference. I only point it out to give that broader understanding
of the data structure. If you look at the first letter of the table number "A"
in not pertabated and "B" is not. The first two Part 3-flow tables total workers
and workers by mode are not pertabated and show 27,725 people living and working in
Cambridge. If you look at tables B302101 (age) and 302012 (industry) they show 27,735
people living and working in Cambridge. The difference of 10 I submit is the effect of
2. In the other tables you reference, except for income I am thinking the drop in the
total is the difference between ALL workers including those in group quarters and just
workers in households. With CTPP tables since many of the tables were developed for travel
modeling their universes are restricted to just workers in households. Right now I do
not have an explanation for the increase in workers you saw with the income table without
talking to some people and digging into it more. Since I worked with all the previous
vintages of CTPP tables and the Bureaus rules have changed I do not want to speculate. It
was encouraging that the B303100 and B303201 were in agreement.
Lets keep the discussion going and hopefully we can get to the bottom of this. Usually it
is something simple but you never know. thanks for airing this.
On 8/12/2019 9:58 AM, Cook, Cliff wrote:
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.
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