In short, it may seem that we’re bombarded by statistics, but the ones we encounter in news reports are only a tiny fraction of all the numbers out there. They have been selected because someone thought we’d find them especially interesting or convincing. In a sense, the numbers that reach us have often been tailored to shock and awe, to capture and hold our attention. Therefore, when we encounter a statistic, it helps to ask who produced that number, and what their agenda might be. In addition, we should watch for attempts to present data in ways that make them seem particularly impressive. Consider these examples.
D1Big Round Numbers
Big round numbers make big impressions. They seem shocking: “I had no idea things were that bad!” They are easy to remember. They are also one of the surest signs that somebody is guessing.
Particularly when advocates are first trying to draw others’ attention to a social problem, they find it necessary to make statistical guesses. If nobody has been paying much attention to the problem, then, in all likelihood, nobody has been bothering to keep accurate records, to count the number of cases. There are no good statistics on it. But as soon as the advocates’ campaign begins to attract the media, reporters are bound to start asking for numbers. Just how common is this problem? How many cases are there? The advocates are going to be pressed for figures, and they are going to have to offer guesses—ballpark figures, educated guesses, guesstimates.
These guesses may be quite sincere. The advocates think this is a serious problem, and so they are likely to think it is a big problem. They spend their days talking to other people who share their concern. If they are going to guess, they are likely to fix on a big round number that confirms their sense of urgency. As a result, their numbers are likely to err on the side of exaggeration.
| LOOK FORThe name says it all: big round numbers |
EXAMPLE: ORNITHICIDE
When birds fly into windows, the collisions are often fatal. These are sad events. We enjoy looking out our windows at birds, and we hate to think that our windows are responsible for killing those same birds. This seems to be just one more way that people disrupt nature.
In recent years, a big round estimate for the number of fatal bird collisions each year has found its way into the news media. For example, an architecture professor interviewed on National Public Radio in 2005 put the annual number of bird collision deaths at one billion. The reporter conducting the interview expressed skepticism: “How accurate is that number, do you think? How would you ever calculate something like that?” After all, a billion is a lot. It is one thousand millions–a very large, very round number. But the professor insisted that the one-billion figure was “based on very careful data.”1
Well, not exactly. The previous best estimate for bird deaths due to fatal window collisions was 3.5 million–a whole lot less than a billion. This estimate simply assumed that the area of the continental United States is about 3.5 million square miles, and that each year, on average, one bird per square mile died after striking a window.2 In other words, the 3.5-million figure wasn’t much more than a guess.
Convinced that that number was too low, an ornithologist decided to do some research.3 He arranged to have residents at two houses keep careful track of bird collisions at their homes: one in southern Illinois, the other in a suburb in New York. By coincidence, the Illinois house belonged to former neighbors of ours–an older couple who loved birds and who built a custom home with lots of windows, surrounded by trees, bushes, bird feeders, and so on. Their house was a bird magnet. Over a two-year period, they observed 59 fatal bird strikes at their home. (In contrast, we lived for eight years in a house a few hundred yards away; however, most of our windows were screened, and, so far as we knew, no birds died striking our house during those years.)
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
