Chicago Traffic Analysis Zones 9-Counties 1990 Population: 7,429,181 Area (sq. miles): 137 Number of...
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Chicago Chicago Traffic Analysis Zones Traffic Analysis Zones 9-Counties 1990 Population: 7,429,181 Area (sq. miles): 137 Number of zones: 14,127 People per zone: 526 Resident workers: 3,563,603 Work place workers: 3,635,769 Workers at home: 76,371 Total households: 2,675,257 Counties include: Cook, DuPage, Grundy, Kane, Kankakee, Kendall, Lake, McHenry, Disclosure and Utility of Census Journey-to-Work Flow Data from the American Community Survey Disclosure and Utility of Census Journey-to-Work Flow Data from the American Community Survey Is There a Right Balance? Is There a Right Balance? Ed Christopher (Federal Highway Administration) Ed Christopher (Federal Highway Administration) Nanda Srinivasan (Cambridge Systematics, Inc.) Nanda Srinivasan (Cambridge Systematics, Inc.) Early in 2003 the transportation community contracted with the Census Bureau to produce the CTPP2000, a special tabulation. A special tabulation is made up of user defined tables and falls outside the “standard” products distributed by the Census Bureau like SF1, SF3, and PUMS. With the 2000 decennial data, the Census Bureau required all special tabulations to have disclosure avoidance techniques applied to them. For CTPP2000 this meant the institution of rounding and threshold techniques in addition to the already applied procedures of data swapping and imputation. The specific disclosure rules for the ACS after 5 years of data collection are likely to be similar, if not stricter than to those used for CTPP2000. In this poster the effects of rounding and thresholds on the CTPP are exposed along with an examination of their effects under the ACS. Franklin County (Columbus, OH) Franklin County (Columbus, OH) Total Workers Living and Working in the County (Census 2000) = 508,393 Total Workers Living and Working in the County (Census 2000) = 508,393 County-County Place-Place Tract-Tract Zone-Zone CTPP2000 CTPP2000 Table 3-01 (No Thresholds) 508,395 508,361 500,426 487,979 Percent Loss 0.00% 0.01% 1.57% 4.02% Table 3-06 (Thresholds) 508,395 507,604 358,170 177,643 Percent Loss 0.00% 0.16% 29.55% 65.06% Total Workers Living and Working in the County (ACS, 3-yr) = 498,220 Total Workers Living and Working in the County (ACS, 3-yr) = 498,220 ACS (1999, ACS (1999, 2000 and 2000 and 2001) 2001) Table 3-01 (No Thresholds) 498,220 498,168 447,446 na Percent Loss 0.00% 0.01% 10.19% Table 3-03 (Thresholds) 498,220 495,840 233,920 na Percent Loss 0.00% 0.48% 53.05% Douglas County (Omaha, NE) Douglas County (Omaha, NE) Total Workers Living and Working in the County (Census 2000) = 213,642 Total Workers Living and Working in the County (Census 2000) = 213,642 County-County Place-Place Tract-Tract Zone-Zone CTPP2000 CTPP2000 Table 3-01 (No Thresholds) 213,640 213,655 211,565 209,315 Percent Loss 0.00% -0.01% 0.97% 2.03% Table 3-06 (Thresholds) 213,640 213,640 157,334 109,247 Percent Loss 0.00% 0.00% 26.36% 48.86% Total Workers Living and Working in the County (ACS, 3-yr) = 209,970 Total Workers Living and Working in the County (ACS, 3-yr) = 209,970 ACS (1999, ACS (1999, 2000 and 2000 and 2001) 2001) Table 3-01 (No Thresholds) 209,970 209,970 190,287 190,145 Percent Loss 0.00% 0.00% 9.37% 9.44% Table 3-03 (Thresholds) 209,970 209,960 124,103 79,665 Percent Loss 0.00% 0.00% 40.89% 62.06% Pima County (Tucson, AZ) Pima County (Tucson, AZ) Total Workers Living and Working in the County (Census 2000) = 359,296 Total Workers Living and Working in the County (Census 2000) = 359,296 County-County Place-Place Tract-Tract Zone-Zone CTPP2000 CTPP2000 Table 3-01 (No Thresholds) 359,295 359,281 357,695 354,566 Percent Loss 0.00% 0.00% 0.45% 1.32% Table 3-06 (Thresholds) 359,295 358,204 264,146 126,218 Percent Loss 0.00% 0.30% 26.48% 64.87% Total Workers Living and Working in the County (ACS, 3-yr) = 354,130 Total Workers Living and Working in the County (ACS, 3-yr) = 354,130 ACS (1999, ACS (1999, 2000 and 2000 and 2001) 2001) Table 3-01 (No Thresholds) 354,130 354,164 314,781 316,878 Percent Loss 0.00% -0.01% 11.11% 10.52% Table 3-03 (Thresholds) 354,130 352,635 197,924 87,319 75.34% County and County and State Name State Name Most Most Detailed Detailed Geography Geography Percent of Percent of Housing Units Housing Units Sampled Sampled Percent of Percent of Population Population Responding Responding CTPP CTPP ACS ACS CTPP CTPP ACS ACS Pima AZ TAZ 12.5 13.4 12.7 8.6 San Fran. CA TAZ 11.7 9.6 11.8 5.5 Broward FL TAZ 11.7 9.5 11.5 5.9 Lake IL TAZ 14.3 10.3 14.4 6.6 Hampden MA Tract 13.4 14.6 13.5 9.4 Douglas NE TAZ 13.9 15.2 13.9 10.5 Bronx NY Tract 11.3 10.2 11.6 4.4 Franklin OH Tract 14.1 9.4 14.1 6.2 Multnomah OR Tract 14.1 15.0 14.0 10.0 Key Data Issues Key Data Issues ACS ACS CTPP CTPP Rounding Rules Same Same Group Quarters No Yes Threshold Rules Same Same Extended Allocation No Yes Housing Units Sampled 12.7% 13.5% Population Responding 8.4% 13.6% Los Angeles Los Angeles Census Tracts Census Tracts Boston Boston Census Block Groups Census Block Groups 6-Counties 1990 Population:14,640,832 Area (sq. miles): 578 Number of Tracts: 3,934 People per Tract: 3,722 Resident workers: 6,844,948 Work place workers: 6,849,916 Workers at home: 187,091 Total households: 4,942,075 Counties include: Imperial, Los Angeles, Orange, Riverside, San Benardino and Ventura Counties (see below) 1990 Population: 4,056,947 Area (sq. miles): 809 Number of BGs: 3,850 People per BG: 1,054 Resident workers: 2,073,508 Work place workers: 2,201,473 Workers at home: 50,989 Total households: 1,507,077 Counties include: All MCDs in 1990 Boston definition including parts of Middlesex, Essex Worcester, Suffolk, Norfolk, Bristol and Plymouth OD Pairs Lost Due To Thresholds OD Pairs Lost Due To Thresholds Franklin County (Columbus, OH) Franklin County (Columbus, OH) CTPP OD Pairs w/Trips CTPP OD Pairs w/Trips ACS OD Pairs w/Trips ACS OD Pairs w/Trips Without Thresholds With Thresholds Percent Lost Without Thresholds With Thresholds Pairs Lost Place-Place 384 306 20% 334 229 31% Tract-Tract 23,289 6,794 71% 13,380 2,459 82% BG-BG 44,266 5,045 89% ----- ----- ----- Douglas County (Omaha, NE) Douglas County (Omaha, NE) CTPP OD Pairs w/Trips CTPP OD Pairs w/Trips ACS OD Pairs w/Trips ACS OD Pairs w/Trips Without Thresholds With Thresholds Percent Lost Without Thresholds With Thresholds Pairs Lost Place-Place 15 14 7% 15 14 7% Tract-Tract 8,830 3,044 66% 7,485 2,089 72% TAZ-TAZ 14,389 3,081 79% 11,269 1,809 84% Pima County (Tucson, AZ) Pima County (Tucson, AZ) CTPP OD Pairs w/Trips CTPP OD Pairs w/Trips ACS OD Pairs w/Trips ACS OD Pairs w/Trips Without Thresholds With Thresholds Percent Lost Without Thresholds With Thresholds Pairs Lost Place-Place 318 209 34% 270 175 35% Tract-Tract 13,320 4,644 65% 10,573 2,911 72% TAZ-TAZ 26,781 3,179 88% 18,168 1,675 91% CTPP2000 Disclosure Avoidance Rules CTPP2000 Disclosure Avoidance Rules Study Areas Used for Rounding Analysis Study Areas Used for Rounding Analysis Number of Trips per OD Pair Chicago – TAZ Chicago – TAZ Los Angeles – Tract Los Angeles – Tract Boston – BG Boston – BG Frequency Frequency Percent Percent Cum Cum Percen Percen t Frequency Frequency Percent Percent Cum Cum Percen Percen t Frequenc Frequenc y Percent Percent Cum Cum Percen Percen t 1 1,075 0.3 0.3 377 0.1 0.1 110 0.1 0.1 2 9,227 2.7 3.0 1,727 0.4 0.5 863 0.5 0.5 3 6,372 1.9 4.9 4,278 1.0 1.5 1,248 0.7 1.2 4 10,825 3.2 8.0 13,161 3.2 4.7 4,711 2.6 3.8 5 29,259 8.5 16.6 30,138 7.3 12.0 13,696 7.5 11.3 6 47,016 13.7 30.3 44,779 10.8 22.8 23,588 13.0 24.3 7 50,173 14.6 44.9 46,764 11.3 34.0 26,467 14.5 38.8 8 43,484 12.7 57.6 42,957 10.3 44.4 24,073 13.2 52.1 9 33,459 9.8 67.4 34,907 8.4 52.8 18,914 10.4 62.5 10+ 111,921 32.6 100.0 196,098 47.2 100.0 68,278 37.5 100.0 Total 342,811 100 415,186 100 181,948 100 Number and Percent of Trips per OD Pair Number and Percent of Trips per OD Pair Source: 1990 CTPP data for Commuters who live in the region, excludes workers at home. Source: 1990 CTPP data for Commuters who live in the region, excludes workers at home. ACS Urban Test Counties in the NCHRP 8-48 Database ACS Urban Test Counties in the NCHRP 8-48 Database Comparison of Key Data Issues Comparison of Key Data Issues in the Analysis Data Sets in the Analysis Data Sets Tabl e Content 1 Total Workers (1) 2 Means of Transportation (7) by Vehicles Available (3) 3 Poverty Status (3) 4 Minority Status (2) 5 Household Income (8) 6 Means of Transportation (17) 7 Means of Transportation (4) by Household Income (4) 8 Mean Travel Time by Means of Transportation to Work (7) and Time Leaving Home for Work (2) 9 Median Travel Time by Means of Transportation to Work (7) and Time Leaving Home for Work (2) 10 Aggregate Number of Vehicles by Time Leaving Home for Work (2) 11 Number of Workers per Vehicle by Time Leaving Home for Work (2) 12 Aggregate Number of Carpools by Time Leaving Home for Work (2) 13 Number of Workers per Carpool by Time Leaving Home for Work (2) 14 Aggregate Travel Time by Means of Transportation to Work (7) and Time Leaving Home for Work (2) Part 3 – Worker Flow Tables with Disclosure Rules Part 3 – Worker Flow Tables with Disclosure Rules No record threshold Must have 3 unweighted records What is Rounding? For confidentiality considerations the Census Bureau rounded all CTPP 2000 tables except for those containing means, medians, and standard deviation values. The rounding rules were simple. Values of zero remained zero. Values between 1 and 7 were rounded to 4. And values of 8 or more were rounded to the nearest multiple of 5. Rounding Analysis Plan Take 1990 un-rounded CTPP data, apply the 2000 rounding rules and examine the affects of rounding on the data. How does rounded and un-rounded data compare? Was rounding values between 1 and 7 to 4 a good decision? Did the rounding rules have a different affect on different geographical Summary Levels? What are Thresholds? The threshold rule stated that no data would be provided for any Origin-Destination pair that had 3 or less records (trips) before weighting. The Analysis Plan Take data CTPP2000 and ACS test data for three areas and compare the number of trips/workers and the number of OD pairs with Thresholds and without. Data Used for Analysis CTPP2000 Part 3 Tables 3-01 and 3-06 ACS NCHRP 8-48 Test Data Part 3 Tables 3-01 and 3-03 Workers who lived in and worked in study area including those working at home Three study areas or Counties Area and Summary Area and Summary Level Level Rounding Rule Rounding Rule of Seven of Seven Total Total Commuters Commuters Lost Lost Commuters Commuters Percent Percent Lost Lost Chicago, IL (TAZ) Without 3,487,232 0 0.00 With 3,342,963 144,269 4.14 Los Angeles, CA (Tracts) Without 6,657,857 0 0.00 With 6,505,471 152,386 2.29 Boston, MA (Block Groups) Without 2,022,519 0 0.00 With 1,941,612 80,907 4.00 Rounding Rounding 1. 1. Produces Inconsistencies Among Produces Inconsistencies Among CTPP Table Values CTPP Table Values 2. 2. Caused a Systematic Undercount Caused a Systematic Undercount of Workers of Workers 3. 3. Did not Show a Significant Did not Show a Significant Noticeable Difference on Summary Noticeable Difference on Summary Levels Levels 4. 4. Rounding to 5 Would Have Been Rounding to 5 Would Have Been Better Better 5. 5. Was Not Well Received by Users Was Not Well Received by Users Thresholds Thresholds 1. 1. Eliminates Most of the OD Pairs and Eliminates Most of the OD Pairs and Commuters Commuters 2. 2. Renders the Flow Data Useless Renders the Flow Data Useless 3. 3. Undermines the Utility of Small Undermines the Utility of Small Area Data Area Data 4. 4. Was Not Well Received by Users Was Not Well Received by Users Boston Block Group Summary 0 2 4 6 8 10 12 14 16 1 2 3 4 5 6 7 Number of Trips per OD Pair Percent of All Trips Can You Find the Midpoint? — It is not 4! Can You Find the Midpoint? — It is not 4! 40 30 20 10 1 2 3 4 5 6 7 Taz Tract BG Source: 1990 Part 3 CTPP. Source: 1990 Part 3 CTPP. Data Used for Analysis 1990 Part 3 Resident Workers (commuters who lived in region), excluding those who worked at home Three Regions (Chicago, Los Angeles, and Boston) Three Summary Levels or small area geographies (TAZs, Tracts and Block Groups) Number of Trips per OD Pair Percent of All Trips Source: NCHRP 8-48 Test Dataset Tables Workers Lost Due To Rounding and Thresholds Workers Lost Due To Rounding and Thresholds Source: CTPP2000 Part 3 and ACS NCHRP 8-48 Test Data Part 3. Source: CTPP2000 Part 3 and ACS NCHRP 8-48 Test Data Part 3. Source: CTPP2000 Part 3 and ACS NCHRP 8-48 Test Data Part 3. Part 1 – At Residence (121 Tables) Part 1 – At Residence (121 Tables) All Tables Rounded All Tables Rounded Zero = 0 Zero = 0 1 through 7 = 4 1 through 7 = 4 8 through ∞ = Nearest Multiple of 5 8 through ∞ = Nearest Multiple of 5 Part 2 – At Workplace (68 Tables) Part 2 – At Workplace (68 Tables) All Tables Rounded All Tables Rounded Part 3 – Worker Flows (14 Tables) Part 3 – Worker Flows (14 Tables) All Tables Rounded All Tables Rounded Some Tables with Thresholds Some Tables with Thresholds 1990 Commuters Lost Due to Rounding 1990 Commuters Lost Due to Rounding
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Transcript of Chicago Traffic Analysis Zones 9-Counties 1990 Population: 7,429,181 Area (sq. miles): 137 Number of...
ChicagoChicagoTraffic Analysis ZonesTraffic Analysis Zones
9-Counties1990 Population: 7,429,181
Area (sq. miles): 137Number of zones: 14,127
People per zone: 526
Resident workers: 3,563,603Work place workers: 3,635,769
Workers at home: 76,371Total households: 2,675,257
Counties include: Cook, DuPage, Grundy, Kane, Kankakee, Kendall, Lake, McHenry, and Will
Disclosure and Utility of Census Journey-to-Work Flow Data from the American Community SurveyDisclosure and Utility of Census Journey-to-Work Flow Data from the American Community SurveyIs There a Right Balance?Is There a Right Balance?
Ed Christopher (Federal Highway Administration)Ed Christopher (Federal Highway Administration)Nanda Srinivasan (Cambridge Systematics, Inc.)Nanda Srinivasan (Cambridge Systematics, Inc.)
Early in 2003 the transportation community contracted with the Census Bureau to produce the CTPP2000, a special tabulation. A special tabulation is made up of user defined tables and falls outside the “standard” products distributed by the Census Bureau like SF1, SF3, and PUMS. With the 2000 decennial data, the Census Bureau required all special tabulations to have disclosure avoidance techniques applied to them. For CTPP2000 this meant the institution of rounding and threshold techniques in addition to the already applied procedures of data swapping and imputation. The specific disclosure rules for the ACS after 5 years of data collection are likely to be similar, if not stricter than to those used for CTPP2000. In this poster the effects of rounding and thresholds on the CTPP are exposed along with an examination of their effects under the ACS.
Early in 2003 the transportation community contracted with the Census Bureau to produce the CTPP2000, a special tabulation. A special tabulation is made up of user defined tables and falls outside the “standard” products distributed by the Census Bureau like SF1, SF3, and PUMS. With the 2000 decennial data, the Census Bureau required all special tabulations to have disclosure avoidance techniques applied to them. For CTPP2000 this meant the institution of rounding and threshold techniques in addition to the already applied procedures of data swapping and imputation. The specific disclosure rules for the ACS after 5 years of data collection are likely to be similar, if not stricter than to those used for CTPP2000. In this poster the effects of rounding and thresholds on the CTPP are exposed along with an examination of their effects under the ACS.
Franklin County (Columbus, OH)Franklin County (Columbus, OH)
Total Workers Living and Working in the County (Census 2000) = 508,393Total Workers Living and Working in the County (Census 2000) = 508,393
County-County Place-Place Tract-Tract Zone-Zone
CTPP2000CTPP2000
Table 3-01 (No Thresholds) 508,395 508,361 500,426 487,979
Percent Loss 0.00% 0.01% 1.57% 4.02%
Table 3-06 (Thresholds) 508,395 507,604 358,170 177,643
Percent Loss 0.00% 0.16% 29.55% 65.06%
Total Workers Living and Working in the County (ACS, 3-yr) = 498,220Total Workers Living and Working in the County (ACS, 3-yr) = 498,220
ACS (1999, 2000 ACS (1999, 2000 and 2001)and 2001)
Table 3-01 (No Thresholds) 498,220 498,168 447,446 na
Percent Loss 0.00% 0.01% 10.19%
Table 3-03 (Thresholds) 498,220 495,840 233,920 na
Percent Loss 0.00% 0.48% 53.05%
Douglas County (Omaha, NE) Douglas County (Omaha, NE)
Total Workers Living and Working in the County (Census 2000) = 213,642Total Workers Living and Working in the County (Census 2000) = 213,642
County-County Place-Place Tract-Tract Zone-Zone
CTPP2000CTPP2000
Table 3-01 (No Thresholds) 213,640 213,655 211,565 209,315
Percent Loss 0.00% -0.01% 0.97% 2.03%
Table 3-06 (Thresholds) 213,640 213,640 157,334 109,247
Percent Loss 0.00% 0.00% 26.36% 48.86%
Total Workers Living and Working in the County (ACS, 3-yr) = 209,970Total Workers Living and Working in the County (ACS, 3-yr) = 209,970
ACS (1999, 2000 ACS (1999, 2000 and 2001)and 2001)
Table 3-01 (No Thresholds) 209,970 209,970 190,287 190,145
Percent Loss 0.00% 0.00% 9.37% 9.44%
Table 3-03 (Thresholds) 209,970 209,960 124,103 79,665
Percent Loss 0.00% 0.00% 40.89% 62.06%
Pima County (Tucson, AZ)Pima County (Tucson, AZ)
Total Workers Living and Working in the County (Census 2000) = 359,296Total Workers Living and Working in the County (Census 2000) = 359,296
County-County Place-Place Tract-Tract Zone-Zone
CTPP2000CTPP2000
Table 3-01 (No Thresholds) 359,295 359,281 357,695 354,566
Percent Loss 0.00% 0.00% 0.45% 1.32%
Table 3-06 (Thresholds) 359,295 358,204 264,146 126,218
Percent Loss 0.00% 0.30% 26.48% 64.87%
Total Workers Living and Working in the County (ACS, 3-yr) = 354,130Total Workers Living and Working in the County (ACS, 3-yr) = 354,130
ACS (1999, 2000 ACS (1999, 2000 and 2001)and 2001)
Table 3-01 (No Thresholds) 354,130 354,164 314,781 316,878
Percent Loss 0.00% -0.01% 11.11% 10.52%
Table 3-03 (Thresholds) 354,130 352,635 197,924 87,319
Percent Loss 0.00% 0.42% 44.11% 75.34%
County and County and State NameState Name
MostMost DetailedDetailed
GeographyGeography
Percent of Housing Percent of Housing Units SampledUnits Sampled
Percent of Population Percent of Population RespondingResponding
CTPPCTPP ACSACS CTPPCTPP ACSACS
Pima AZ TAZ 12.5 13.4 12.7 8.6
San Fran. CA TAZ 11.7 9.6 11.8 5.5
Broward FL TAZ 11.7 9.5 11.5 5.9
Lake IL TAZ 14.3 10.3 14.4 6.6
Hampden MA Tract 13.4 14.6 13.5 9.4
Douglas NE TAZ 13.9 15.2 13.9 10.5
Bronx NY Tract 11.3 10.2 11.6 4.4
Franklin OH Tract 14.1 9.4 14.1 6.2
Multnomah OR Tract 14.1 15.0 14.0 10.0
Key Data IssuesKey Data Issues ACSACS CTPPCTPP
Rounding Rules Same Same
Group Quarters No Yes
Threshold Rules Same Same
Extended Allocation No Yes
Housing Units Sampled 12.7% 13.5%
Population Responding 8.4% 13.6%
Los AngelesLos AngelesCensus TractsCensus Tracts
BostonBostonCensus Block GroupsCensus Block Groups
6-Counties1990 Population:14,640,832
Area (sq. miles): 578Number of Tracts: 3,934People per Tract: 3,722
Resident workers: 6,844,948Work place workers: 6,849,916
Workers at home: 187,091Total households: 4,942,075
Counties include: Imperial, Los Angeles, Orange, Riverside, San Benardino and Ventura
Counties (see below)1990 Population: 4,056,947
Area (sq. miles): 809Number of BGs: 3,850People per BG: 1,054
Resident workers: 2,073,508Work place workers: 2,201,473
Workers at home: 50,989Total households: 1,507,077
Counties include: All MCDs in 1990 Boston definition including parts of Middlesex, Essex Worcester, Suffolk, Norfolk, Bristol and Plymouth
OD Pairs Lost Due To ThresholdsOD Pairs Lost Due To Thresholds
Franklin County (Columbus, OH)Franklin County (Columbus, OH)
CTPP OD Pairs w/TripsCTPP OD Pairs w/Trips ACS OD Pairs w/TripsACS OD Pairs w/Trips
Without
ThresholdsWith
ThresholdsPercent
LostWithout
ThresholdsWith
ThresholdsPairsLost
Place-Place 384 306 20% 334 229 31%
Tract-Tract 23,289 6,794 71% 13,380 2,459 82%
BG-BG 44,266 5,045 89% ----- ----- -----
Douglas County (Omaha, NE) Douglas County (Omaha, NE)
CTPP OD Pairs w/TripsCTPP OD Pairs w/Trips ACS OD Pairs w/TripsACS OD Pairs w/Trips
Without
ThresholdsWith
ThresholdsPercent
LostWithout
ThresholdsWith
ThresholdsPairs Lost
Place-Place 15 14 7% 15 14 7%
Tract-Tract 8,830 3,044 66% 7,485 2,089 72%
TAZ-TAZ 14,389 3,081 79% 11,269 1,809 84%
Pima County (Tucson, AZ)Pima County (Tucson, AZ)
CTPP OD Pairs w/TripsCTPP OD Pairs w/Trips ACS OD Pairs w/TripsACS OD Pairs w/Trips
Without
ThresholdsWith
ThresholdsPercent
LostWithout
ThresholdsWith
ThresholdsPairs Lost
Place-Place 318 209 34% 270 175 35%
Tract-Tract 13,320 4,644 65% 10,573 2,911 72%
TAZ-TAZ 26,781 3,179 88% 18,168 1,675 91%
CTPP2000 Disclosure Avoidance RulesCTPP2000 Disclosure Avoidance Rules
Study Areas Used for Rounding AnalysisStudy Areas Used for Rounding Analysis
Number of Trips per OD Pair
Chicago – TAZChicago – TAZ Los Angeles – TractLos Angeles – Tract Boston – BGBoston – BG
FrequencyFrequency PercentPercent CumCumPercentPercent FrequencyFrequency PercentPercent CumCum
PercentPercent FrequencyFrequency PercentPercent CumCumPercentPercent
1 1,075 0.3 0.3 377 0.1 0.1 110 0.1 0.1
2 9,227 2.7 3.0 1,727 0.4 0.5 863 0.5 0.5
3 6,372 1.9 4.9 4,278 1.0 1.5 1,248 0.7 1.2
4 10,825 3.2 8.0 13,161 3.2 4.7 4,711 2.6 3.8
5 29,259 8.5 16.6 30,138 7.3 12.0 13,696 7.5 11.3
6 47,016 13.7 30.3 44,779 10.8 22.8 23,588 13.0 24.3
7 50,173 14.6 44.9 46,764 11.3 34.0 26,467 14.5 38.8
8 43,484 12.7 57.6 42,957 10.3 44.4 24,073 13.2 52.1
9 33,459 9.8 67.4 34,907 8.4 52.8 18,914 10.4 62.5
10+ 111,921 32.6 100.0 196,098 47.2 100.0 68,278 37.5 100.0
Total 342,811 100 415,186 100 181,948 100
Number and Percent of Trips per OD PairNumber and Percent of Trips per OD Pair
Source: 1990 CTPP data for Commuters who live in the region, excludes workers at home.Source: 1990 CTPP data for Commuters who live in the region, excludes workers at home.
ACS Urban Test Counties in the NCHRP 8-48 DatabaseACS Urban Test Counties in the NCHRP 8-48 Database
Comparison of Key Data IssuesComparison of Key Data Issuesin the Analysis Data Setsin the Analysis Data Sets
Table Content
1 Total Workers (1)
2 Means of Transportation (7) by Vehicles Available (3)
3 Poverty Status (3)
4 Minority Status (2)
5 Household Income (8)
6 Means of Transportation (17)
7 Means of Transportation (4) by Household Income (4)
8 Mean Travel Time by Means of Transportation to Work (7) and Time Leaving Home for Work (2)
9 Median Travel Time by Means of Transportation to Work (7) and Time Leaving Home for Work (2)
10 Aggregate Number of Vehicles by Time Leaving Home for Work (2)
11 Number of Workers per Vehicle by Time Leaving Home for Work (2)
12 Aggregate Number of Carpools by Time Leaving Home for Work (2)
13 Number of Workers per Carpool by Time Leaving Home for Work (2)
14 Aggregate Travel Time by Means of Transportation to Work (7) and Time Leaving Home for Work (2)
Part 3 – Worker Flow Tables with Disclosure RulesPart 3 – Worker Flow Tables with Disclosure Rules
No recordthreshold
Must have 3 unweighted
records
What is Rounding?For confidentiality considerations the Census Bureau rounded all CTPP 2000 tables except for those containing means, medians, and standard deviation values. The rounding rules were simple. Values of zero remained zero. Values between 1 and 7 were rounded to 4. And values of 8 or more were rounded to the nearest multiple of 5.
Rounding Analysis PlanTake 1990 un-rounded CTPP data, apply the 2000 rounding rules and examine the affects of rounding on the data. How does rounded and un-rounded data compare? Was rounding values between 1 and 7 to 4 a good decision? Did the rounding rules have a different affect on different geographical Summary Levels?
What are Thresholds?The threshold rule stated that no data would be provided for any Origin-Destination pair that had 3 or less records (trips) before weighting.
The Analysis PlanTake data CTPP2000 and ACS test data for three areas and compare the number of trips/workers and the number of OD pairs with Thresholds and without.
Data Used for Analysis CTPP2000 Part 3 Tables 3-01
and 3-06
ACS NCHRP 8-48 Test Data Part 3 Tables 3-01 and 3-03
Workers who lived in and worked in study area including those working at home
Three study areas or Counties
Area and Summary LevelArea and Summary Level Rounding Rule Rounding Rule of Sevenof Seven
TotalTotalCommutersCommuters
LostLostCommutersCommuters
PercentPercentLostLost
Chicago, IL (TAZ)
Without 3,487,232 0 0.00
With 3,342,963 144,269 4.14
Los Angeles, CA (Tracts)
Without 6,657,857 0 0.00
With 6,505,471 152,386 2.29
Boston, MA (Block Groups)
Without 2,022,519 0 0.00
With 1,941,612 80,907 4.00
RoundingRounding1.1. Produces Inconsistencies Among CTPP Produces Inconsistencies Among CTPP
Table ValuesTable Values2.2. Caused a Systematic Undercount of Caused a Systematic Undercount of
WorkersWorkers3.3. Did not Show a Significant Noticeable Did not Show a Significant Noticeable
Difference on Summary LevelsDifference on Summary Levels4.4. Rounding to 5 Would Have Been BetterRounding to 5 Would Have Been Better5.5. Was Not Well Received by UsersWas Not Well Received by Users
ThresholdsThresholds1.1. Eliminates Most of the OD Pairs and Eliminates Most of the OD Pairs and
CommutersCommuters2.2. Renders the Flow Data UselessRenders the Flow Data Useless3.3. Undermines the Utility of Small Area DataUndermines the Utility of Small Area Data4.4. Was Not Well Received by UsersWas Not Well Received by Users
Boston Block Group SummaryBoston Block Group Summary
00
22
44
66
88
1010
1212
1414
1616
11 22 33 44 55 66 77
Number of Trips per OD PairNumber of Trips per OD Pair
Percent of All TripsPercent of All Trips
Can You Find the Midpoint? — It is not 4!Can You Find the Midpoint? — It is not 4!
4040
3030
2020
1010
11 22 33 44 55 66 77
Taz
Tract
BG
Taz
Tract
BG
Source: 1990 Part 3 CTPP.Source: 1990 Part 3 CTPP.
Data Used for Analysis 1990 Part 3 Resident Workers (commuters who lived in region), excluding those who worked at home Three Regions (Chicago, Los Angeles, and Boston) Three Summary Levels or small area geographies (TAZs, Tracts
and Block Groups)
Number of Trips per OD PairNumber of Trips per OD Pair
Percent of All TripsPercent of All Trips
Source: NCHRP 8-48 Test Dataset TablesSource: NCHRP 8-48 Test Dataset Tables
Workers Lost Due To Rounding and ThresholdsWorkers Lost Due To Rounding and Thresholds
Source: CTPP2000 Part 3 and ACS NCHRP 8-48 Test Data Part 3. Source: CTPP2000 Part 3 and ACS NCHRP 8-48 Test Data Part 3.
Source: CTPP2000 Part 3 and ACS NCHRP 8-48 Test Data Part 3. Source: CTPP2000 Part 3 and ACS NCHRP 8-48 Test Data Part 3.
Part 1 – At Residence (121 Tables)Part 1 – At Residence (121 Tables)All Tables RoundedAll Tables Rounded
Zero = 0Zero = 01 through 7 = 41 through 7 = 48 through ∞ = Nearest Multiple of 58 through ∞ = Nearest Multiple of 5
Part 2 – At Workplace (68 Tables)Part 2 – At Workplace (68 Tables)All Tables RoundedAll Tables Rounded
Part 3 – Worker Flows (14 Tables)Part 3 – Worker Flows (14 Tables)All Tables RoundedAll Tables RoundedSome Tables with ThresholdsSome Tables with Thresholds 1990 Commuters Lost Due to Rounding1990 Commuters Lost Due to Rounding
