Census > ACS Main > How to Use the Data > User Notes |
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Year |
American Community Survey User Note |
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2007 | Modification Made in 2007 ACS Weighting Methodology for Orange County, CA The review of the 2007 ACS tabulations revealed large discrepancies between the final 2007 ACS estimate of total population and the 2007 population estimates from the Population Estimates Program for a set of places in Orange County, CA. These same areas showed a similar pattern of differences in the 2005 and 2006 ACS estimates. An additional adjustment to the weights was introduced in the weighting for Orange County to remove the source of the discrepancy. The adjustment was aimed at forcing the weighted distribution of housing units in the ACS sample to match the distribution of housing units on our sampling frame. The weighting adjustment was applied at the census tract level. As a result, it has eliminated most of the large discrepancies originally found for places in Orange County. This modification was also made to the 2006 ACS weighting methodology. |
2007 | Modification Made in 2007 ACS Weighting Methodology for Orleans and St. Bernard Parishes, LA The review of the 2007 operational data discovered evidence that suggests a high incidence of misclassification of uninhabitable units as vacant units. The effect of misclassification was almost entirely removed through a modification in the weighting methodology for Orleans and St. Bernard Parishes. The effect of the weighting adjustment was to down-weight units that had the vacancy status of "Other Vacant". This modification resulted in more consistent and accurate ACS estimates of the number of vacant units and "persons per household" in these two parishes. This modification was also made to the 2006 ACS weighting methodology. |
2007 | County Estimates of Group Quarters Population The weighting for the group quarters population is controlled at the state level. For that reason, users should expect that the ACS estimate for the group quarters population to be consistent with the Population Estimates Program only at the state level. At the county level, the ACS estimate will typically be different from the Population Estimates Program due to sampling variability. Like estimates of total population, data users who require an estimate of the group quarters population at the county level should use the official estimates from the Population Estimates Program. |
2007 | Year-to-year Change in the ACS Group Quarters Population Estimates at the Sub-State Level The weighting for the group quarters (GQ) population is controlled at the state level, but not at sub-state levels. For this reason, users may observe greater fluctuations in year-to-year ACS estimates of the GQ population at sub-state levels than at state levels. The causes of these fluctuations typically are the result of either GQs that have closed or where the current population of the GQ is significantly different than the expected population as reflected on the sampling frame. Substantial changes in the ACS GQ estimates can impact ACS estimates of total population characteristics for areas where either the GQ population is a substantial proportion of the total population or where the GQ population may have very different characteristics than the total population as a whole. Users can assess the impact that year-to-year changes in sub-state GQ total population estimates have on the changes in total ACS population estimates by accessing Table B26001 on American Fact Finder. Users should also use their local knowledge to help determine whether the year-to-year change in the ACS estimate represents a real change in the GQ population or may be the result of the lack of adequate population controls for sub-state areas. |
2007 | 2007 ACS -- Race Reporting Among Hispanic Respondents in Abilene, TX MSA In Abilene, TX, the Census Bureau has identified a large increase in the percent of Hispanics reporting their race as White Alone and a large decrease in the percent of Hispanics reporting their race as Some Other Race. This increase is likely the result of a problem in the data collection process and probably does not represent real change. Data users should use caution when interpreting the data for Hispanic respondents who reported their race as White or Some Other Race. |
2006 | Modification Made in 2006 ACS Weighting Methodology for Orange County, CA The review of the 2006 ACS tabulations revealed large discrepancies between the final 2006 ACS estimate of total population and the 2006 intercensal population estimates for a set of places in Orange County, CA. These same areas showed a similar pattern of differences in the 2005 ACS tabulated estimates. An additional adjustment to the weights was introduced in the weighting for Orange County to remove the source of the discrepancy. The adjustment was aimed at forcing the weighted distribution of housing units in the ACS sample to match the distribution of housing units on our sampling frame. The weighting adjustment was applied at the census tract level. As a result, it has eliminated most of the large discrepancies originally found for places in Orange County. |
2006 | Modification Made in 2006 ACS Weighting Methodology for Orleans and St. Bernard
Parishes, LA The review of the 2006 operational data discovered evidence that suggests a high incidence of misclassification of uninhabitable units as vacant units. The effect of misclassification was almost entirely removed through a modification in the weighting methodology for Orleans and St. Bernard Parishes. The effect of the weighting adjustment was to down-weight units that had the vacancy status of "Other Vacant". This modification resulted in more consistent and accurate ACS estimates of the number of vacant units and "persons per household" in these two parishes. |
2006 | Modification Made in 2006 ACS Weighting Methodology-Family Equalization As a result of our continuous effort to improve the quality of the estimates the 2006 weighting methodology was modified in order to ensure total consistency between the estimates of householders, households, and occupied housing units. This has not been the case prior to 2006. With this data release, the estimates of occupied housing units, households, and householders will all be equal. In addition, the modification also reduces the differences between estimates of spouses and married-couple households and between the estimates of unmarried partners and unmarried-partner households. See the Changes to the Estimation (pdf) for detailed information regarding which tables are most affected and the impact on the estimates had this methodology been applied in 2005. |
2006 | Sub-state Estimates of Group Quarters Population The weighting for the group quarters population is controlled at the state level. For that reason, users should expect that the ACS estimate for the group quarters population to be consistent with the Population Estimates Program only at the state level. For sub-state areas, the ACS estimate will typically be different from the Population Estimates Program due to sampling variability. Like estimates of total population, data users who require an estimate of the group quarters population at the county level should use the official estimates from the Population Estimates Program. |
2005 | Special Note to ACS Data Users - 2005 Here is how we determine which sub-state geographic areas meet the ACS population threshold
of 65,000 for publishing estimates for that area: Wherever possible, we use the most current
estimate of the total resident population from official Census Bureau Population Estimates
Program (PEP). This number includes both household and group quarters population. PEP
provides this estimate for counties, incorporated places, and sub-county areas (e.g. townships),
which have a functioning government. If the PEP estimate for any of these areas is 65,000 or
more, then we publish ACS data products for that area. However, since the ACS sample is still a
sample of the housing unit population, the ACS estimates will often be lower than the PEP
estimates. In some cases, the ACS estimate of total (housing unit) population will be less than
65,000. This is an indication that the total resident population for that geographic area is over
65,000 (although probably very close to 65,000). There are 52 geographic areas where this
occurs, and they are shown in the table below.
Data Release Rules Even with the population size thresholds described earlier, in certain geographic areas some very detailed tables might include estimates whose reliability is unacceptable. Data release rules, based on the statistical reliability of the survey estimates, will be used starting with the 2005 ACS data released in the summer of 2006. These release rules apply only to the single-year and three-year data products. The main data release rule for the ACS tables works as follows. Every base table consists of a series of estimates. If more than half the estimates are not statistically different from 0 (at a 90 percent confidence level), then the table fails. Each estimate is subject to sampling variability that can be summarized by its standard error. Dividing the standard error by the estimate yields the coefficient of variation (CV) for each of the estimates. (If the estimate is 0, a CV of 100 percent is assigned.) To implement this requirement for each table at a given geographic area, CVs are calculated for each of the table's estimates, and the median CV value is determined. If 13-11 the median CV value for the table is less than or equal to 61 percent, the table passes for that geographic area; if it is greater than 61 percent, the table fails. Tables that are too sparse will fail this test. In that case, the table will not be published for that geographic area. Whenever a table fails, a simpler table that collapses some of the detailed lines together can be substituted for the original, more detailed table. The data release rules are then applied to the simpler table. If it passes, the simpler table is released. If it fails, none of the estimates for that particular table is released for this geographic area. These release rules are applied to single-year period estimates and multi-year period estimates based on three years of sample data. No data release rules are applied to the estimates based on five years of sample data. For more information go to the Design and Methodology document, the link to it is http://www.census.gov/acs/www/Downloads/tp67.pdf |