12 Aug
2019
12 Aug
'19
11:56 a.m.
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 perturbation.
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:
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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