1. What is item nonresponse?
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.
2. How does the ACS correct for 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. The first of these two methods is known as assignment, while the second is referred to as allocation.
Assignment involves logical imputation where a response to one question implies the value for a missing response to another question. For example, school grade or level attending can often be used to assign a value to highest degree or level of school completed.
Allocation, on the other hand, involves using statistical procedures, such as within-household or nearest neighbor matrices populated by donors, to impute for missing values.
3. Why is it important to measure item nonresponse?
So that data users can judge the completeness of the data in which the survey estimates are based. Final estimates can be adversely impacted when item nonresponse is high and bias can be introduced if the characteristics of the nonrespondents differ from those reported by respondents. Item nonresponse and unit nonresponse both contribute to potential bias in the estimates.
4. How does the ACS measure item nonresponse?
Item nonresponse is measured through the calculation of allocation rates which are published with the survey estimates. The Census Bureau calculates measures of item nonresponse for two distinct universes. Data.census.gov includes allocation tables specific to the tabulation universes. This Quality Measures Web page includes allocation rates for the universe that was eligible for editing and imputation. In some instances these will be the same, but in many instances they will differ. For example, we edit and impute data collected for educational attainment for the total population 3 years and over, so that is the universe referenced to calculate the allocation rates shown on the Quality Measures Web page. However, the tables for educational attainment in data.census.gov are restricted to the population age 25+ and therefore the imputation tables on data.census.gov are restricted to this universe. The specific universe associated with each of these Quality Measures are shown in the tables, displayed below the title of each item.
5. Why did item nonresponse increase between 2012 and 2013?
The majority of the increase in item nonresponse rates between 2012 and 2013 was due to the cessation of part of the Failed Edit Follow Up operation in late 2012. Incomplete mail forms were no longer sent for follow up, which increased the amount of item nonresponse. For more information, see the User Note.
6. How are item allocation rates calculated?