1. Norwegian Institute of Public Health, Oslo 0213, Norway
2. Columbia University Medical Center, New York 10032-3784, USA
3. Norwegian National Advisory Unit on Ageing and Health, Vestfold Hospital Trust, Tønsberg, Norway
4. University of Oslo, Forskningsveien 3A, 0373 Oslo, Norway
5. Department of Geriatric Medicine, Oslo University Hospital, Oslo, Norway