Exploring participant attrition in a longitudinal follow-up of older adults: the Global Longitudinal Study of Osteoporosis in Women (GLOW) Hamilton cohort.

Attrition in this ageing cohort was selective to some participant characteristics. Minimising potential bias associated with such non-random attrition would require targeted measures to achieve maximum possible follow-rates among the high-risk groups identified and dealing with specific reasons for attrition in the study design and analysis.