1. Office for National Statistics The Time Use Survey 2005 Office for National Statistics 2006 http://www.statistics.gov.uk/cci/article.asp?id=1600
2. Office for Official Publications of the European Communities How Europeans Spend Their Time: Everyday Life of Women and Men Office for Official Publications of the European Communities 2004 http://epp.eurostat.ec.europa.eu/cache/ITY_OFFPUB/KS-58-04-998/EN/KS-58-04-998-EN.PDF
3. Bureau of Labor Statistics (BLS) of the U.S. Department of Labor American time use survey - 2005 results announced by BLS 2006 http://www.bls.gov/tus/
4. Population sampling in European air pollution exposure study, EXPOLIS: comparisons between the cities and representativeness of the samples;Rotko;J Exp Anal Environ Epidemiol,2000