In psychology and social research, unmatched count, or item count, is a technique to improve, through anonymity, the number of true answers to possibly embarrassing or self-incriminating questions.
It is very simple to use but yields only the number of people bearing the property of interest and leads to a larger sampling error than direct questions.
Since the interviewer does not know how they arrived at that number, it is safe to answer the awkward question truthfully.
Due to the unmatched count of items, the number of people who answered "yes" to the awkward question can be mathematically deduced.
The number of "yes" answers in the control group is called the baseline.