The objective of this research was to conduct cognitive testing of experimental questions to be added to the end of a sample of cases in the Coverage Followup (CFU) operation during the 2010 Census. These experimental questions are a part of the Census Program Evaluations and Experiments (CPEX). The experimental questions will gather data on households who reported an indication of overcount or undercount on their initial census response, but then did not respond to the CFU interview accordingly (i.e., did not mention another address or person, respectively), or cases where a potential duplicate was identified in the data, but no indication of a second address was reported during the CFU interview. In order to test this, we used cases from the 2008 Census Dress Rehearsal North Carolina test site that fit one of three criteria: 1) the household marked “yes” to the undercount question in the initial census form, but did not list any potential additional people during the CFU interview; 2) the household marked an affirmative overcount category for at least one household member on the initial census form, but did not flag that person as having another place to stay during the CFU interview; and 3) a suspected person duplicate was identified through computer matching of the census data, and the CFU interview did not reveal an additional address for that person. Results are presented in three sections below, corresponding to the above three criteria.