1. Departments of Clinical Epidemiology (C.L.M., F.W.D.), 2300 RC Leiden, The Netherlands
2. Public Health and Primary Care (J.G., W.P.J.d.E.), 2300 RC Leiden, The Netherlands
3. Gerontology and Geriatrics (A.J.M.d.C.), Leiden University Medical Center, 2300 RC Leiden, The Netherlands