Definitions for "Callbacks"
The re-approach of a sample member after previous contact attempts have been unsuccessful. Callbacks reduce the likelihood of nonresponse error by improving the contact rate.
Repeated attempts to contact a respondent who cannot be interviewed on an earlier attempt.  A reasonable number of callbacks should be made to increase overall response and the probability that the survey results are representative of the population.
The selection process by which actors return for a second or third tryout.