1. U.S. Census Bureau. International Data Base. 2013. http://www.census.gov/population/international/data/idb/informationGateway.php .
2. Chodzko-Zajko WJ, Proctor DN, Singh MAF, Minson CT, Nigg CR, Salem GJ, et al. Exercise and physical activity for older adults. Med Sci Sports Exerc. 2009;41:1510–30.
3. Armstrong T, Bauman A, Davies J. Physical activity patterns of Australian adults. In: Physical activity patterns of Australian adults. Australia: Australian Institute of Health and Welfare; 2000.
4. ABS. 2009–10 Household Expenditure Survey (HES). Canberra, Australia: Australian Bureau of Statistics; 2011.
5. Jones J, Saad L. Gallup poll social series: economy and personal finance. USA: Gallup; 2014.