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Mathematical modelers at the London School of Hygiene and Tropical Medicine have shown that even a 60 % effective microbicide , used in 73 low income countries by only 20 % of the women who are reached by health care could prevent 2.5 million new HIV infections over a three year period . And this is how she intends to continue , although at 73 , Cohen has passed the usual age of retirement . For historical reasons , the EU continues to dominate Africa 's external trade , accounting for 73 per cent of the region 's exports and providing 57 per cent of its imports . Brazil is the global industry 's 800 pound gorilla - - it is the world 's largest producer of caned spirits , accounting for 73 percent of global consumption in 1999 . The larger of the studies , conducted in 73 patients with Alzheimer 's disease , showed no beneficial effect of trazodone at all . In both cases , the within-population ( clusters ) components of variance dominated the AMOVA , accounting for 73 % to 79 % of the variation , with less than five percent representing variation between heterotic groups . The commercial minimum size , currently at 73 inches - - current fork length . But concussions were more common among males , accounting for 73 percent of injuries for boys and 40 percent of injuries for girls in high school .