Stratified Sampling : Of a population which can be divided into different subpopulations (called strata), sampling carried out in such a way that specific proportions of the sample are drawn from the different strata (ISO, 1977)
International Programme on Chemical Safety IPCS (A joint venture of the United Nations Environment Programme UNEP, the International Labour Organisation, ILO and the World Health Organization WHO), Glossary of Terms on Chemical Safety for Use in IPCS Publications, World Health Organization, Division of Environmental Health, World Health Organization, Geneva, Switzerland, ILO 1996-2010. http://www.ilo.org/legacy/english/protection/safew ork/cis/products/safetytm/glossary.ht, (IPCS Chem Sfty - Brit) {103}