Improving Reliability of Small-Area ACS Data January 14, 2015 - - PowerPoint PPT Presentation

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Improving Reliability of Small-Area ACS Data January 14, 2015 - - PowerPoint PPT Presentation

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Improving Reliability of Small-Area ACS Data January 14, 2015 Transportation Research Board 94 th Annual Meeting Paul Reim Boston Region Metropolitan Planning Organization Agenda 1. The need for, and problems with, small-area ACS data 2. A

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Boston Region Metropolitan Planning Organization

Improving Reliability of Small-Area ACS Data

January 14, 2015 Paul Reim Transportation Research Board 94th Annual Meeting

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Agenda

  • 1. The need for, and problems with, small-area

ACS data

  • 2. A solution: the ‘touch method’
  • 3. Future trends
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The Need for Small-Area Data

  • Equity analyses: Title VI, EJ
  • Corridor studies
  • Development reviews
  • Travel demand model inputs
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MPO Model in 1990

Software: UTPS Modeled area:

  • 986 TAZs
  • 887 Census tracts
  • 3,623 Census block groups
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MPO Model in 2002

Software: EMME/2 Modeled area:

  • 2,727 TAZs
  • 894 Census tracts
  • 3,324 Census block groups
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MPO Model in 2014

Software: TransCAD Modeled area:

  • 2,727 TAZs
  • 976 Census tracts
  • 3,341 Census block groups
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Statistical Testing and the ACS

Two useful publications:

  • Multiyear Accuracy of the Data
  • Instructions for Applying Statistical Testing
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Statistical Testing and the ACS

Important statistics:

  • Margin of error (MOE): published with data
  • Standard error (SE)
  • Coefficient of variation (CV)
  • Z statistic
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Example: HH by Income Quartile

  • Re-state the ACS estimates as proportions
  • Apply the proportions to 2010 Census

counts

  • Allocate the resulting estimates to TAZ

using factors derived from 2010 Census block statistics

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Example: Using Block Group Data

Percentage of table cells with CV <= 0.3:

  • 2000 Census SF3: 85%
  • 2006-2010 ACS:

41%

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Example: Using Tract Data

Percentage of table cells with CV <= 0.3:

  • 2000 Census SF3: 92%
  • 2006-2010 ACS:

87%

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Solution: the Touch Method

2014 ACS Users Conference Presentations by:

  • Ken Hodges, Nielsen Company
  • Ben Horwitz: Greater New Orleans

Community Data Center

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Solution: the Touch Method

Combine each block group’s estimates with those of its neighbors.

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Example: Touch Method

Percentage of table cells with CV <= 0.3:

  • 2010 ACS published:

41%

  • 2010 ACS touch method: 76%
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Example: Compare Estimates

  • The touch method has produced block

group estimates with better margins of error

  • The next step: evaluate whether the

differences between estimates are statistically significant

  • How? The Z statistic
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Example: Compare Estimates

  • Difference is statistically significant if Z is

less than -1.645 or greater than +1.645

  • We can use the touch method if the vast

majority of its estimates do not differ significantly from published estimates

  • In this example, the difference is

insignificant for 89% of cells in the table

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Future Trends

  • ACS Sample size was increased beginning

in 2011

  • Improvements in margins of error and other

statistics are already showing up

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Example: 2012 ACS Block Group

Percentage of table cells with CV <= 0.3:

  • 2006-2010 ACS published:

41%

  • 2008-2012 ACS published:

68%

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SLIDE 19

Conclusions

  • Small-area 2010 ACS estimates have been

shown to be less reliable than corresponding 2000 Census estimates

  • The touch method may provide more usable

ACS estimates at the block group level

  • Increased sample size beginning in 2011 has

had positive results