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2. European Commission Report: Active ageing and solidarity between generations: A statistical portrait of the European Union 2012, 2012 Edition (2012)
3. Department of Economic and Social Affairs of the United Nations, http://esa.un.org/wpp/unpp/panel_population.htm (last access May 02, 2013)
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5. U.S. Department of Health and Human Services: A Profile of Older Americans (2011)