Background: Previous research has found that a "web-push" approach to data collection, which involves contacting people by mail to request an Internet survey response while withholding a paper response option until later in the contact process, consistently achieves lower response rates than a "paper-only" approach, whereby all respondents are contacted and requested to respond by mail.
Method: An experiment was designed, as part of the Millennium Cohort Family Study, to compare response rates, sample representativeness, and cost between a web-push and a paper-only approach; each approach comprised 3 stages of mail contacts. The invited sample (n = 4,935) consisted of spouses married to U.