Since the 1950s, which is as far back in time as data from the National Oceanic and Atmospheric Administration (NOAA) extends, the frequency of strong-to-violent tornadoes has been roughly level. Some people claim that tornados have become more common, but as NOAA explains, this is an artifact of "increased National Doppler radar coverage, increasing population, and greater attention to tornado reporting." In contrast, strong-to-violent tornadoes "would have likely been reported even during the decades before Doppler radar use became widespread and practices resulted in increasing tornado reports." Thus, they are more accurate and salient measure of U.S. tornado trends.