Value of semiannual postcard contact in a longitudinal cohort study

Background: Various approaches have been utilized for retaining participants in longitudinal studies including maintaining up-to-date contact information. Postcards are sent to Millennium Cohort Study participants each Memorial and Veterans Day to honor their military service, thank them for their continued participation, and prompt them to update their contact information. While semiannual contact is suspected to engage members in the study, it is unknown whether periodic contact prompts participants to update their contact information.

Methods: Descriptive investigations of Cohort participants who updated their contact information online and had a change of address were completed. Weekly percents of participants who updated their contact information over the total number of participants were graphically displayed. Univariate analyses were completed to temporally compare the volume of updated contact information associated with Memorial and Veterans Day postcards.

Results: Almost 80% of Cohort participants moved between 2002 and 2006. Of these, 9% voluntarily updated their contact information online. Of those who updated their contact information online, 65% updated their contact information at least once within 2 weeks of semiannual postcard contact. Participants were significantly more likely to update their contact information during the 2-week period immediately after receipt of the semiannual postcards (average = 1.09%) compared with the 2 weeks immediately prior (to the delivery of postcards average = 0.03%) (p < 0.001).

Results: The US military is a mobile population. Semiannual appreciatory contact is an effective way to maintain communication with study participants while prompting updates of contact information.