The following items represent changes in the estimation procedures used for school district, county, and state poverty estimates for 2011 relative to the estimation procedures used for 2009. These changes reduce the comparability of the estimates between years and should be considered when making such comparisons. See General Cautions about Comparisons of Estimates and Guidance for Making Year-to-Year Comparisons.
There were no changes in the list of county-level entities in 2011 relative to 2009 estimates, and boundary changes were minor adjustments associated with the decennial 2011 tabulations.
For the 2011 estimates, the only change in methodology was the incorporation of population estimates based on the decennial 2011 counts. Control populations used for the 2011 release of the American Community Survey (ACS), all population-based inputs, and the denominator for the published SAIPE poverty rates are derived from these decennial 2011 counts.
For the 2011 release, two changes to the methods for state-level estimates were implemented. The source of the District of Columbia estimates is described in the next paragraph. The other change was the incorporation of population estimates based on the decennial 2011 counts. Control populations used for the 2011 release of the American Community Survey, and all denominator for ratios used for inputs, as well as the denominator for the published SAIPE poverty rates are derived from these decennial 2011 counts.
Starting in 2009, estimates of poverty for ages 5-17 for the District of Columbia (DC) are obtained from the county model, instead of the state model. For poverty of the other age groups and for median household income, estimates for DC are still obtained from a version of the state model where DC is included in the estimation procedures. This 2009 procedural change is described in more detail in 2009 Estimation Changes Detail.
For all other states, SAIPE estimates are obtained from a version of the state model where DC is not included. This is a change from 2009, where the state estimates were obtained from a model containing DC.
School District Estimates
There were no changes in the list of school districts or their grade-range coverage in 2011 relative to 2009 estimates. A few minor boundary changes were associated with the decennial 2011 tabulations. All such changes had less than 0.1% impact on population counts.
One change to methodology is the basis for the school district-level population estimates for 2011. These estimates are now based on the decennial 2011 population counts, benchmarked to sum to the Census Bureau’s official county-level population estimates for July 1, 2011.
The other substantial change in the methodology is the replacement of the decennial 2000 sample estimates of school-age poverty as one of the inputs to the school district estimation process with estimates derived from the latest five-year sample of the American Community Survey (ACS 2006-10). In the 2011 decennial census, no long-form survey questions were included. This decennial sample data has now been replaced by the continuous measurement ACS. So the SAIPE program also replaced the decennial sample estimates as an input to the school district process.
There are tradeoffs in using the two different sources as an input to the school district estimation process. The survey associated with the decennial 2000, in general, has lower errors associated with sampling than the ACS five-year survey. To the ACS advantage, the ACS five-year estimates are more timely relative to the decennial 2000 as an input to 2011 estimation. Combining the two effects, preliminary evaluation indicates that the ACS five-year estimate as an estimator of current-year poverty represents an improvement in relative error compared to using the decennial 2000 estimate. The impact on the final SAIPE school-district estimates will thus yield an improvement in precision, but a fuller evaluation is required to give more detail on how the uncertainty of these estimates have improved.