You need to be careful with these figures. The figure 2.2 billion (2,200,000,000) includes all children, including those harmed. Out of these children 1.5 million are harmed (1,500,000), so those not harmed=2,200,000,000-1,500,000=2,198,500,000. The ratio of those harmed to those not harmed is 1,500,000:2,198,500,000=3:4397 or approx 3:4,400, or 1:1467. The fraction of children harmed is 1,500,000/2,200,000,000=3/4400. Because the number of children is small compared to the total population of children, the ratio and the fraction are nearly the same. If you were to work out the ratio of boys to girls in the child population, the ratio and the fraction would be very different, because the number of boys is closer to the number of girls in the child population.