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The decrease in death toll is even more apparent when the rate of death is normalized by the population of the United States, available from the U.S. Census Bureau. (http://www.census.gov/) Prior to 1925, the smoothed rate was relatively constant, showing a slight increase from about 1.6 to 1.8 per million. Since that time, however, the rate has decreased substantially, to a little over 0.11 per million, roughly 1/15th of the long-term average prior to 1925. Many factors, including the beginnings of tornado forecasting, improved communications, spotter networks, and changes in construction, likely have been involved in this decrease [see Doswell et al. (1999) for more discussion].
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