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Locating and retaining research participants for follow-up studies.

Two common pitfalls of longitudinal research are loss of participants over time and inability to locate participants whose contact information has changed. This article is based on our experiences in locating and retaining a sample of caregivers of persons with Parkinson's disease 8-10 years after we last contacted them. The strategies we used resulted in locating 86% of our sample and retaining 80% of those who were eligible. These strategies included asking participants for a backup contact, asking participants if they would be willing to be contacted again for a future study, making the most of existing search engines, keeping in touch, and being flexible, patient, and professional.