Source Texts
Text
Run by researchers in Europe, the Survey of Health, Ageing, and Retirement in Europe (SHARE) is an examination of aging that has attempted to track approximately 120,000 people for several years. Long-running studies like this need a lot of participants not merely for statistical robustness but also because of ______: over such a length of time, a substantial number of participants will withdraw or fall out of contact with the researchers.