Tables Starting with B are perturbated. Tables starting with an A are not. Here is the generalized coding schema for the tables.

"The tables are divided into three parts. Part 1 summarizes the population at their place of residence; Part 2 the workers at their place of work and Part 3 the commuting flow from home to work. Each table has a unique number. The number is partially encoded. Reading from left to right, all tables will begin with a letter, either an ‘A’ or a ‘B’. The ‘A’ means the table is derived directly from standard ACS data while ‘B’ tables have put through a special privacy protection algorithm. The next digit identifies which part the data belongs to--a ‘1’ for part one, ‘2’ for part two and ‘3’ for part three. The next two digits refer to the universe from which the data is drawn. There are 16 different universes and they are listed later on page 13 of this guide. The next digit lets the user know if the table is a univariate (1), two-way (2) or three-way (3) table. The next 2 digits represent a sequential numbering of the tables."
You can read all about the peturbation here: https://www.nap.edu/download/18160


On 8/12/2019 12:10 PM, Cook, Cliff wrote:

Ed

 

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?

 

Thanks

 

Cliff

 

From: Ed Christopher <edc@berwyned.com>
Sent: Monday, August 12, 2019 12:57 PM
To: ctpp-news@chrispy.net; Cook, Cliff <ccook@cambridgema.gov>
Cc: Werner, Bailey <bwerner@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 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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-- 
Ed Christopher
Transportation Planning Consultant
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-- 
Ed Christopher
Transportation Planning Consultant
708-269-5237