|Data Dictionary:||ACS 2006 -- 2008 (3-Year Estimates)|
|Data Source:||U.S. Census Bureau|
Universe: Universe: Workers 16 years and over
|ACS 2008-3yr Summary File: Technical Documentation -> Appendix B: Subject Definitions -> Quality Measures -> Imputation Rates|
Missing data for a particular question or item is called item nonresponse. It occurs when a respondent fails to provide an answer to a required item. The ACS also considers invalid answers as item nonresponse. The Census Bureau uses imputation methods that either use rules to determine acceptable answers or use answers from similar housing units or people who provided the item information. One type of imputation, allocation, involves using statistical procedures, such as within-household or nearest neighbor matrices populated by donors, to impute for missing values.
Overall Person Characteristic Imputation Rate
This rate is calculated by adding together the weighted number of allocated items across a set of person characteristics, and dividing by the total weighted number of responses across the same set of characteristics.
Overall Housing Characteristic Imputation Rate
This rate is calculated by adding together the weighted number of allocated items across a set of household and housing unit characteristics, and dividing by the total weighted number of responses across the same set of characteristics. These rates give an overall picture of the rate of item nonresponse for a geographic area.
|ACS 2008-3yr Summary File: Technical Documentation -> Appendix B: Subject Definitions -> Population Variables -> Journey to Work -> Time Leaving Home to Go to Work|
The data on time leaving home to go to work were derived from answers to Question 32. This question was asked of people who indicated in Question 28 that they worked at some time during the reference week, and who reported in Question 30 that they worked outside their home. The departure time refers to the time of day that the respondent usually left home to go to work during the reference week. (See "Reference Week.")
Limitation of the Data
Beginning in 2006, the group quarters (GQ) population is included in the ACS. Some types of GQ populations may have departure time distributions that are different from the household population. The inclusion of the GQ population could therefore have a noticeable impact on the departure time distribution. This is particularly true for areas with a substantial GQ population.
Beginning in 1999, the American Community Survey questions differ from the 1996-1998 questions only in the format of the skip instructions.