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.

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 In that case, the table will not be published for that geographic area.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.