The Census Bureau publishes ACS 1-year, 3-year, and 5-year estimates, with population thresholds set for the ACS 1-year and 3-year estimates to produce reliable data. Here is a brief comparison of the three types of estimates:

1-year Estimates	3-Year Estimates	5-Year Estimates
Published for selected geographic areas with populations of 65,000 or greater	Published for selected geographic areas with populations of 20,000 or greater	Published for all geographic areas including those with a population under 20,000.
Represent the average characteristics over a calendar year	Represent the average characteristics over the 3-year period of time	Represent the average characteristics over the 5-year period of time
Have fewer published geographic areas than the 3-year and 5-year estimates	Have more published geographic areas than the 1-year estimates but fewer than the 5-year estimates	Have more published areas than the 1-year and 3-year estimates

For more information on the ACS estimates, users are encouraged to visit the ACS website http://www.census.gov/acs/www/guidance_for_data_users/estimates/.

Some data values represent unique situations where either the information to be conveyed is an explanation for the absence of data, represented by a symbol in the data display, such as "(X)", or the information to be conveyed is an open-ended distribution, such as 115 or greater, represented by 115+.

The following special data values can appear in the ACS Summary File table as an explanation for the absence of data:

• Missing Value = ""

A missing string indicates that the estimate is unavailable. (This appears in the estimates and margins or error files as two commas adjacent to each other without anything between them, or if the last cell in a data file is filtered then you get a comma followed immediately by a carriage return or EOF.) A missing value indicates when an estimate is missing because of filtering for geographic restrictions, coefficients of variations (CV), or was removed due to the Disclosure Review Board's (DRB) requirements. For more detail on filtering, please visit Chapter 4.4.

• Dot = "."

A dot indicates when the estimate has no sample observations or too few sample observations. In the margin of error files, this value could also indicate that the margin of error is unavailable for a median estimate that has been replaced with a jam value.

• Zero = "0"

A "0" entry in the margin of error column indicates that the estimate is controlled. A statistical test for sampling variability is not appropriate. This is similar to the "*****" symbol used in American FactFinder.

• Negative 1 = "-1"

This indicates that an estimate does not contain a Margin of Error. Tables B00001, B00002, and tables starting with B98 and B99 do not have margin of error (MOE) associated with them. The MOE calculations are set to -1 for these tables.

• Jam Values for Medians

The following is a listing of the jam values for medians. For example, if there is an estimate of "2499" for table B10010, then it does not indicate a dollar amount. It means that the median is somewhere below 2,500 and thus is not calculated.

Jam Value	Actual Meaning	Use for Medians
0	1 or less	Age, Duration of Marriage
9	9.0 or more	Rooms
10	10.0 or less	Gross Rent as Percentage of Income, Owner Costs as Percentage of Income
50	50.0 or more	Gross Rent as Percentage of Income, Owner Costs as Percentage of Income
99	100 or less	Rent, Gross Rent, Selected Monthly Owner Costs, Monthly Housing Costs
101	101 or more	Duration of Marriage
116	115 or more	Age
199	200 or less	Tax
1001	1,000 or more	Selected Monthly Owner Costs
1939	1939 or earlier	Year Built
1969	1969 or earlier	Year Moved In
2001	2,000 or more	Rent, Gross Rent
2010	2010 or later	Year Built, Year Moved In
2499	2,500 or less	Income, Earnings
4001	4,000 or more	Selected Monthly Owner Costs, Monthly Housing Costs
9999	10,000 or less	Value
10001	10,000 or more	Tax
200001	200,000 or more	Income
250001	250,000 or more	Income, Earnings
1000001	1,000,000 or more	Value

B00001, B00002, B98001, and B98002 are sample counts, not estimates, and do not have margin of error (MOE) associated with them. Tables in series B99* imputation tables and B98* (except B98001 and B98002) quality measure tables do not provide margin of error calculations. The margin of error calculations are set to -1 for these tables.

There are a few special rules on how certain margin of error are determined for ACS estimates. The accuracy of the estimate (decimal place) within the detailed tables determines how many digits the margin of error is rounded.

Data users often question why certain ACS estimates are not available. Missing estimates can be caused by data suppression through various methods or restrictions that are applied to ACS data to limit the disclosure of information about individual respondents and to reduce estimates with unacceptable statistical reliability.

Filtering rules, based on statistical reliability of the ACS 1-year and 3-year survey estimates, are used to ensure that Detailed Tables are not released where the majority of the estimates in the Detailed Tables have an unacceptable level of reliability.

Learn more about missing estimates and filtering rules in the data suppression document available on the ACS website at www.census.gov/acs/www/data_documentation/data_suppression/.

The estimates in the summary files are stored using standard notation instead of in scientific notation. The estimates are stored as whole numbers. The largest estimate in the ACS Summary File contains 14 digits.

There are eight tables with more than the maximum 245 cells that cannot fit into a single sequence, so each of these tables is broken into multiple sequence files. The table below shows the tables that contain multiple sequences:

Tables That Are Contained in More Than One Sequence File

Table ID	Table Title
B24121	Detailed Occupation By Median Earnings In The Past 12 Months For The Full-Time, Year-Round Civilian Employed Population 16 Years And Over
B24122	Detailed Occupation By Median Earnings In The Past 12 Months For The Full-Time, Year-Round Civilian Employed Male Population 16 Years And Over
B24123	Detailed Occupation For The Full-Time, Year Round Civilian Employed Population 16 Years And Over
B24124	Detailed Occupation For The Full-Time, Year Round Civilian Employed Male Population 16 Years And Over
B24125	Detailed Occupation For The Full-Time, Year Round Civilian Employed Male Population 16 Years And Over
B24126	Detailed Occupation For The Full-Time, Year Round Civilian Employed Female Population 16 Years And Over

Check Appendix A to verify the sequences for these tables. The last six tables on the list are only produced at the United States national level (summary level 010), and the files for these sequences will be blank for all other summary levels.