Stat-Spotting. Joel Best

      But how do we get to that one-billion estimate? The ornithologist did not extrapolate from the two-house sample. Rather, he found government estimates for the numbers of housing units, commercial buildings, and schools in the United States–a total of 97.6 million structures. He then estimated that each year, on average, between one and ten birds would die from flying into each building’s windows. Thus, he concluded that between 97.6 million and 975.6 million fatal bird strikes occurred annually. Advocates seized on the larger figure, rounded up, and–voilà!–concluded that “very careful data” indicated that one billion birds die each year from window collisions.

      Clearly, a large number of birds die this way. As there is no way to measure this number accurately, we have to make estimates. If we assume one death per square mile, we get 3.5 million deaths; one death per building gets us about 100 million; ten deaths per building gets us a billion. Certainly a billion is a more arresting figure, one that is more likely to receive media coverage.

      However, not everyone agrees with it. One bird-death Web site suggests that only 80 million birds die from window strikes annually (it offers no basis for that figure). However, it states that “pet cats that are allowed to roam free account for some 4 MILLION bird deaths EACH DAY in North America, or over 1 BILLION songbirds each year. This figure does not include the losses resulting from feral cats or wild populations of cats” (emphasis in the original).⁴ Just to put that big round number in perspective, the American Veterinary Medical Association estimates that there are about 71 million pet cats (including, of course, some who are restricted to an indoor lifestyle).⁵ To kill a billion birds, each of those cats would have to kill an average of 14 birds annually. (While I was updating this book in early 2013, a team of researchers estimated that “owned” cats kill 684 million birds annually, while “unowned” cats might kill another 1.7 billion, for a total of 2.4 billion. These figures were produced by multiplying the estimated numbers of cats by estimates for the average kills for owned and unowned animals. [On the issues such calculations raise, see section F.1.])⁶

      D2Hyperbole

      An easy way to make a statistic seem impressive is to use superlatives: “the greatest,” “the largest,” “the most,” “record-setting,” and so on. Superlatives imply comparison; that is, they suggest that someone has measured two or more phenomena and determined which is the most significant.

      But often superlatives amount to hyperbole, colorful exaggerations intended simply to impress. There may have been no real comparison; in fact, people may be unable to agree on an appropriate basis for comparison. It is all very well to say that something is the greatest, but there may be many ways to assess greatness and disagreement about which measure is most appropriate.

      A weak sense of history also encourages the use of hyperbolic comparisons. Even once-sensational events tend to fade with time. Sociologists speak of collective memory, a group’s shared sense of its past. Collective memory is selective; most of what happens is forgotten. A society’s members are more likely to recall things that happened recently, or events that mark pivotal moments in the narrative we call history. Everything else tends to blur, to fall out of consideration.

      

LOOK FORSuperlatives–“the biggest,” “the worst,” and so on

      EXAMPLE: THE WORST DISASTER IN U.S. HISTORY

      The terrible terrorist attacks of September 11, 2001, led some commentators to speak of them as the “worst disaster in American history.” Certainly this was an awful event, but how can we decide whether it was the worst disaster? If we define disaster as any relatively sudden event that kills a large number of people, then we might begin by ranking disasters in terms of the numbers of lives lost. The best estimate for the 9/11 death toll is 3,025 (which counts the passengers and crews of the four planes, as well as those thought to have died at the Pentagon and the World Trade Center). This is indeed a horrific total–greater, as many commentators noted, than the 2,403 killed at Pearl Harbor. Still, it is by no means the largest death toll in a U.S. disaster: the record is probably the 4,263 known to have been killed by the 1900 hurricane that hit Galveston, Texas.