Probes are follow-ups to survey questions used to gain insights on respondents' understanding of and responses to these questions. They are usually administered as open-ended questions, primarily in the context of questionnaire pretesting. Due to the decreased cost of data collection for open-ended questions in web surveys, researchers have argued…

Mailing campaigns are a way to keep longitudinal survey respondents engaged. While mailings usually include a survey answer request, sometimes respondents are contacted between-waves to update contact information or simply to keep respondent contact. Research on the actual impact of these between-wave contacts on response rates is scarce. This…