The world's most polluted places

In order to guide the selection process and the advice of the experts, a methodical approach was adopted. A simple scoring system was used by all members of the Technical Advisory Board in preparing individual lists of the worst ten. The scoring system takes into account the following selection criteria: * The size of the affected population * Severity of the toxin or toxins involved * Impact of children's health and development * Evidence of a clear pathway of contamination * Existing and reliable evidence of health impact Different factors were accorded different weights at the suggestion of the Technical Advisory Board. Given the lack of available data (and the difficulty of obtaining more) the experience and expert judgment of the TAB members was essential in estimating scores for each site. Individual scores for the 35 sites on the were tabulated and this tabulation was then reviewed and discussed by the TAB as a whole, eventually arriving at a consensus on the Top Ten.