Use of advance letters to enhance participant retention in a clinical trial

In randomized clinical trials, participant retention is critical to ensure the validity and unbiased interpretation of study results. Within a multisite trial of individuals with high impact chronic pain, we explored whether a letter mailed in advance of follow-up study assessments at 3-, 6-, and 12-months from randomization improved participant retention. 4063 advance letters were mailed to 2037 participants at least once throughout their study participation. Increases in participant retention and follow-up assessment rates were observed across all study groups, sites, and timepoints. Mailing a letter in advance of follow-up study assessments in this randomized clinical trial improved participant retention.