Sample size for cross-sectional descriptive study Sample size for evaluate lead contamination in children - 403 pairs of children aged 3 to 14 and their parents, including 195 children in Ban Thi and 208 children in Tan Long Sample size for lead contamination in environment: 180 samples, including 60 soils, 60 dringking waters and 60 air samples 2.2.2.2.