comparison between census and acs for license...
TRANSCRIPT
Sara Khoeini
Vetri Vethan Elango
Randall Guensler
Jennifer Indech Nelson
Comparison between Census and ACS for License-Plate-Based
Transportation Analysis
http://transportation.ce.gatech.edu/
Overview
Background
Data Resources
Research Question
Methodology
Statistical Analysis
Conclusion
2
Background
License plate based transportation analysis
o Commutershed
o Travel time studies
o Travel Demand Models
o Demographic Analysis
o Equity issues
Georgia Tech project
o HOV to HOT conversion fleet monitoring
3
Socio-Demographic Data Resources
Census 2000 Long Form
o 17% of population
o Collected during a few months
ACS 2005-2009 Summary File
o 5% of population (1% each year)
o Collected during five years
4
“ACS Warmer but Fuzzier than the
Decennial Census”
- Heather Macdonald
Research Question
Does using census data from 2000 and the ACS 5-
year summary file (2005-2009) for analysis of license
plate data collected in 2006 significantly impact
demographic analysis of commuters?
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Methodology
1. Collect license plate data
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License Plate Data
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Methodology
1. Collect license plate data
2. Match collected license plates with household
locations
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Geocoded License Plates
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Methodology
1. Collect license plate data
2. Match collected license plates with household
locations
3. Assign license plates to census block groups (BGs)
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Assign license plates to BGs
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Commutershed Maps
Methodology
1. Collect license plate data
2. Match collected license plates with household
locations
3. Assign license plates to census block groups
4. Assign census block group socio-demographic
attributes to license plate data
5. Compare ACS and census attributes
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Sample Size
22000 unique license plates
2000 block groups within Atlanta Metro Area
On average, Atlanta Metro Area has:
o ACS ~ 2453 HHs per block groups (2005-2009)
o Census ~ 2015 HHs per block groups (2000)
Data collection sample size:
o ACS ~ 123 HHs per block groups
o Census ~ 335 HHs per block groups
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Socio-Demographic Attributes
Attributes selected for comparison between census
and ACS:
Household income
Household size
Vehicle availability
Travel time to work
Time leaving home
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Income
Adjusted for inflation ($1 in 2000 worth 1.25 in 2009)
Test of normality is rejected
Non-parametric tests: Reject the null hypothesis
Economic Recession
On average, median household income is $9,000
higher compared to ACS
Only 18% of records has less than $5,000 difference
between census and ACS
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Income
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Income (Census minus ACS)
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Household size
Test of normality of data rejected
Non parametric test: Reject the null hypothesis
88% of households have less than 0.2 difference in
household size between Census and ACS.
On average, household size from census is 0.13
higher compared to ACS
Atlanta Metropolitan Area population increased about
18% from Census 2000 to Census 2010
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Household Size
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HHsize (Census minus ACS)
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Vehicle Availability
Weighted average for census: 1.90 vehicles/household
Weighted average for ACS: 1.88 vehicles/household
Test of normality of data rejected
Non parametric test: Reject the null hypothesis
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0 1 2 3 4 5
Census %4.01 %28.37 %47.28 %15.22 %3.86 %1.26
ACS %3.94 %30.77 %45.04 %14.99 %4.08 %1.19
Vehicle Availability
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0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
0 1 2 3 4 5
Census
ACS
Vehicle Availability Histograms
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Vehicle Availability (Census minus ACS)
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Travel Time to Work
Census
0 to 30 min
30 to 45 min
45 to 60 min
60+ min
ACS
0 to 10 min
10 to 15 min
15 to 20 min
20 to 25 min
25 to 30 min
30 to 35 min
35 to 45 min
45 to 60 min
60+ min
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Travel Time to Work
Improvement in detail classification in ACS
Test of normality of data rejected
Non parametric test: Reject the null hypothesis
Weighted average for census: 32.27 min
Weighted average for ACS: 31.83 min
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0-30 min 30-45 min 45-60 min 60+ min
Census 50.10% 25.94% 13.09% 10.87%
ACS 51.78% 25.33% 11.56% 11.33%
Travel Time to Work
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0%
10%
20%
30%
40%
50%
60%
0-30 min 30-45 min 45-60 min 60+ min
Census
ACS
Travel Time to Work Histograms
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Travel Time to Work (Census – ACS)
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Time Leaving Home
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0% 2% 4% 6% 8%
10% 12% 14% 16% 18% 20%
Census
ACS
Conclusion
Statistical tests reject equality of distributions
Practically, major differences for income and minor
differences for other attributes
Different time, sampling methods and sample sizes
are the main reasons for differences
Block group level aggregate data instead of
household level data decreases accuracy
Need for local detailed surveys for transportation
projects
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