United States Census Bureau | An official website of the United States Government
Item Allocation Rates
Definitions
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
[https://www.census.gov/programs-surveys/acs/technical-documentation/user-notes/2013-07.html] .
6. How are item allocation rates calculated?
Allocation rate for item A (state x, year y) =
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Page Last Revised - January 21, 2022