Participant characteristics and study features associated with high retention rates in a longitudinal investigation of type 1 diabetes mellitus.

Background: The Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) Study has sustained an extraordinarily high level of participant involvement for over two decades.

Purpose: In order to identify specific characteristics of EDIC that contributed most strongly to retention, study-designed questionnaires were distributed to 1334 participants.

Methods: Confidential questionnaires were completed during EDIC Years 15-17.