Post on 11-Jan-2016
transcript
Transportation leadership you can trust.
presented topresented to
TRB Census Data for Transportation Planning MeetingTRB Census Data for Transportation Planning Meeting
presented bypresented by
Kevin TierneyKevin TierneyCambridge Systematics, Inc.Cambridge Systematics, Inc.
May 12, 2005May 12, 2005
Learning to Use the ACS for Transportation PlanningReport on NCHRP Project 8-48
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National Cooperative Highway Research Program Project 8-48Project Activities
Review current and potential use of census-related data in transportation planning
Compare residence-based, workplace-based and home-to-work outputs from ACS and census long form for use in transportation planning applications
Prepare ACS guidebook
Recommend new transportation data products based on ACS data
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ACS for Transportation PlanningBenefits
Key Census Bureau objectives are likely to be achieved with ACS implementation
• Improve the year 2010 Decennial Census
• Operational schedules and budgets close to predicted levels
ACS data quality is likely to be superior to that of the Census Long Form in terms of nonsampling error
ACS data will be available more frequently
ACS data will be more timely
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ACS for Transportation PlanningChallenges
Sampling error is higher for ACS than for the Long Form (smaller sample sizes)
Data disclosure avoidance will prevent many smaller area analyses that transportation users would like to do, including some that are possible with Census 2000 data
ACS differences from the Census Long Form place limits on our ability to bridge analyses between Year 2000 data and ACS data
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Data Quality ImprovementACS Three Year Averages versus Census 2000 Long Form
CharacteristicCharacteristicACSACS
(1999-2001)(1999-2001) Census 2000Census 2000
Self Completion Non-Response Rate 44.7% 31.9%
Total Housing Unit Non-Response Rate 4.4% 9.7%
Occupied Housing Unit Non-Response Rate 5.2% 8.7%
Allocation Rates
Population Item Total Allocation Rate 6.5% 11.2%
Occupied Housing Unit Total Allocation Rate 7.7% 15.8%
Vacant Housing Unit Total Allocation Rate 23.2% 19.8%
Population and Occupied Housing Unit Total Rate 6.9% 12.8%
Sample Completeness Rates
Housing Sample Completeness 92.9% 90.3%
Household Population Sample Completeness 90.4% 91.1%
Source: Census Bureau, 2004.
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Data TimelinessImproved Transportation Planning Analyses
Analyses of large geographic areas using the most recent Decennial Census data may require the use of data that is 12 to 14 years old
The same analyses using the most recent ACS data can use data that is 8 to 19 months old
Smaller area analyses will require the combination of data from the past several years, but not nearly as far back as the Decennial Census data
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Data FrequencyImproved Transportation Planning Analyses
ACS can better temporally match with other transportation data sources
• Household and on-board surveys
• Transportation ground count data
• Transportation level-of-service data
ACS supports the development of time series trend analyses
• Transportation trend analyses
• Demographic / land-use analyses
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Sample SizeChallenges for Transportation Planning Analyses
Wider confidence intervals
Need for multiyear averaging
Additional threats of sample loss
• Potential future funding limitations
• Voluntary, rather than mandatory participation
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Sample SizeConfidence Levels
Sampling error is higher for ACS than for the Long Form (smaller sample sizes)
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Tract Number
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Sample SizeMulti-year Data Averaging
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Sample SizeChallenges of Analyzing Different Multiyear Periods
Percentage of Zero-Vehicle Households by County Subdivision
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Sample SizeChallenges of a voluntary ACS
Making ACS voluntary, rather than mandatory, will result in:
• Significant reduction in the self-completion mail response rate (over 20 %)
• Increase in annual costs by at least $ 59.2 million to maintain reliability
• And/or reduction in the reliability of estimates because of the reduction in the total number of completed interviews
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Disclosure LimitationsChallenges for Transportation Planning Analyses
Disclosure limits will significantly limit small area analyses commonly performed by transportation planners
Example of disclosure effects on Census 2000 vs. ACS for Multnomah County
Data Part 3: Without Thresholds
Part 3: With Thresholds Part 1
Total Records
Total Workers
Total Records
Total Workers
Total Workers
Census 2000 8,228 207,120 2,644 147,080 199,220
ACS 6,368 181,563 1,673 118,234 202,024
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Comparisons with Census 2000 Demographic Estimates
Estimate CategoryEstimate CategoryACS (1999-2001) – ACS (1999-2001) –
Census 2000Census 2000
Sex Small
Age Moderate
Race Large*
Hispanic Origin Large
Relationship Large
Tenure Moderate
Household by Type Large
Housing Occupancy Large
Source: Census Bureau, 2004.
* Large is defined as nine or more of 36 test counties; small as fewer than four counties.
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Comparisons with Census 2000 Social Estimates
Estimate CategoryEstimate CategoryACS (1999-2001) – ACS (1999-2001) –
Census 2000Census 2000
School Enrollment Moderate
Educational Attainment Moderate
Marital Status Moderate
Grandparents as Caregivers Small
Disability Large*
Nativity and Place of Birth Moderate
Region of Birth/Foreign Born Small
Language Spoken at Home Large
Ancestry Large
Source: Census Bureau, 2004.
* Large is defined as nine or more of 36 test counties; small as fewer than four counties.
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Comparisons with Census 2000 Housing Estimates
Estimate CategoryEstimate CategoryACS (1999-2001) – ACS (1999-2001) –
Census 2000Census 2000
Units in StructureUnits in Structure Large*Large*
Year Structure BuiltYear Structure Built LargeLarge
Number of RoomsNumber of Rooms LargeLarge
Year Householder Moved into UnitYear Householder Moved into Unit SmallSmall
Number of VehiclesNumber of Vehicles ModerateModerate
House Heating FuelHouse Heating Fuel ModerateModerate
Occupants per RoomOccupants per Room LargeLarge
Housing ValueHousing Value ModerateModerate
Mortgage Status and Mortgage Status and Selected Owner CostsSelected Owner Costs SmallSmall
Source: Census Bureau, 2004.
* Large is defined as nine or more of 36 test counties; small as fewer than four counties.
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Comparisons with Census 2000 Economic Estimates
Estimate CategoryEstimate CategoryACS (1999-2001) – ACS (1999-2001) –
Census 2000Census 2000
Employment Status Large*
Commuting to Work Moderate
Occupation Small
Industry Small
Class of Worker Moderate
Household Income Moderate
Income by Type Large
Family Income Small
Poverty Status Small
Source: Census Bureau, 2004.
* Large is defined as nine or more of 36 test counties; small as fewer than four counties.
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Comparisons with Census 2000 Questionnaire and Data Collection Differences
Questionnaire and data collection implementation differences
• Residency definition
• Reference dates
• Minor wording changes
Questionnaire changes over time will further hinder comparison to Decennial Census and previous ACS data
Geographic definition differences
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Comparisons with Census 2000 Questionnaire Resident Definition Differences
Residency definitions are different between Long Form and ACS
• Long Form: usual residence concept− One place where the person spends most of the time
• ACS: current residence concept and the “two month” rule− Recognizes that people can live in more than one place over
the course of a year
− Suits the ACS because of continuous data collection
− Is especially important in seasonal areas
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Comparisons with Census 2000 Questionnaire Reference Period Differences
Reference time periods are different between Long Form and ACS
• Long Form: reference period for a characteristic is a point in time April 1 of the Decennial year
• ACS: reference period for a characteristic is: − An average over 12 months for annual estimates
− An average over 3 years for a 3-year moving average estimate
− An average over 5 years for a 5-year moving average estimate
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Comparisons with Census 2000 Questionnaire Wording Differences
The wording of some questions is different between Long Form and ACS
• Wording and order of introductory data items− ACS collects detailed information on 5 household members
− Long Form collects detailed information on 6 household members
• Wording differences in the instructions for the housing questions
• Effect on trend analysis when there are wording changes
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Comparisons with Census 2000 Geographic Definition Differences
ACS annual and multi-year estimates summarized by the geographic definitions of the final year of the estimates
Definitional changes and annexations need to be accounted for
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Guidebook ACS User Concerns
Census Data Analyses
• Descriptive Analyses
• Trend Analyses
• Transportation Market Analyses
• Travel Survey Development and Analyses
• Travel Demand Modeling Analyses
User Concerns
• Data Frequency Improvements
• Data Timeliness Improvements
• Sample Size Limitations
• Multiyear Averaging Issues
• Data Disclosure Issues
• Bridging between Census 2000 and ACS
• Data Presentation
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Considerations in Defining Transportation Data Products and Special Tabulations
Data needs vary by transportation users
Considerably more transportation planning data may be available from standard ACS tabulations than from standard Decennial Census products
Census Bureau and FHWA have raised concerns about how analysts will treat overlapping multiyear averages
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Considerations in Defining Transportation Data Products and Special Tabulations
Availability of flow data special tabulations with acceptable suppression is in question
Ability to define customized geographic areas for tabulations will be limited
Opportunity to average more than five years of data to increase sample sizes, but the number of years that can be pooled together will reach a practical limit especially in fast growing areas