1. What is Unit Nonresponse?
Unit nonresponse is the failure to obtain the minimum required information from an eligible housing unit or group quarters (GQ) person in the sample. For the ACS, response rates are subtracted from 100 percent to measure unit nonresponse.
Unit nonresponse occurs when respondents are unable or unwilling to participate, interviewers are unable to locate addresses or respondents, or when other barriers exist to completing the interview.
2. How does the ACS adjust for unit nonresponse?
The ACS uses noninterview adjustment methods to give a higher weight to interviewed units and interviewed GQ persons. See Accuracy of the Data for more information on how the noninterview adjustment is calculated.
3. Why is it important to measure unit nonresponse?
We measure it because it has a direct effect on the quality of the data. If the rate of unit nonresponse is high, it increases the chance that the final survey estimates may reflect bias. Estimates may reflect bias if the characteristics of nonresponding units differ from the characteristics of responding units.
4. How does the ACS measure unit nonresponse?
The Census Bureau calculates survey response rates to measure unit nonresponse in the ACS. The survey response rate is the ratio of the estimate of units interviewed after data collection is complete to the estimate of all units that should have been interviewed. Separate rates are calculated for housing unit response and GQ person response. For housing units, this means all interviews after mail, internet, telephone and personal visit follow-up. (Internet data collection began in 2013, and telephone follow-up interviewing ceased in 2017.) For GQ persons, this means all interviews after the personal visit. Interviews include complete and partial interviews with enough information to be processed.
To accurately measure unit nonresponse the ACS must estimate the universe of cases eligible to be interviewed and the survey noninterviews; that is, all eligible units in personal visit follow-up are given the appropriate weight as are all the noninterviews.
5. What are the primary reasons for unit nonresponse in the ACS?
The Census Bureau classifies all final noninterviews by one of the following Reasons for Noninterviews to understand why unit nonresponse occurred:
6. Why does the Census Bureau weight the survey response rate?
Weighting is used because not all housing units or GQ persons have the same probability of selection. The ACS sample design includes differential sampling and subsampling rates. (Refer to the Accuracy of the Data for more information about the use of differential sampling and subsampling in the ACS.) Weighting accounts for the different probabilities of selection as a result of sampling and subsampling.
7. How are survey response rates calculated?