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CTPP Data Products

Using Tables from Part 3 of CTPP: A note of caution

To protect individual confidentiality, the Census Bureau introduced rounding and thresholds.

Rounding

For a discussion on rounding, please read www.fhwa.dot.gov/planning/census_issues/ctpp/status_report/sr0404.cfm. To minimize the effects of rounding, we suggest replacing any cell value equal to 4 with 5.

Thresholds

Three unweighted observations were required for Tables 3-03 to 3-07. Small geography (eg. tract-tract, taz-taz) are severely impacted.

The picture conveys that Tables 3-01, 3-02, and 3-08 to 3-14 are not subject to the three record threshold. The tables subject to thresholds are 3-03 through 3-07. The full listing of CTPP Tables are available at http://www.fhwa.dot.gov/planning/census_issues/ctpp/data_products/tables.cfm

At small area geography (anything more detailed than state-place summary level) data from Tables 3-03, 3-04, 3-05, and 3-06 are severely affected, and should be used with caution. For example, the following table shows severe loss of worker counts when using table 3-06 for Pima County, AZ.

Summary Level

Table 3-01

(Without Threholds)

Table 3-06 (Thresholds)

Workers

Pairs

Workers

Pairs

Tract-Tract

357,695

13,320

264,146

3,179

Zone-Zone

354,566

26,781

126,,218

4,644

Updated: 05/09/2011
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