Multistage Cluster Sampling : Cluster sampling with more than two stages, each sampling being made on aggregates (or clusters) in which the clusters already obtained by the preceding sampling have been divided (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}
International Union of Pure and Applied Chemistry IUPAC, Glossary for Chemists of Terms Used in Toxicology, Prepared for publication by J.H. Duffus, NC., USA 1993. http://www.inchem.org/documents/harmproj/harmproj/ harmproj1.pdf & http://old.iupac.org/reports/1993/6509duffus/c.htm l, (IUPAC/ Tox - Amer) {107}