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strong criticisms of even FDA-approved medications by an aggressive consumer advocate, Dr. Sidney Wolfe. Does that tax-avoidance maneuver you’re hearing about seem a bit fishy? The IRS has lots of information about tax scams that it would like to share with you. Has your uncle Bob sent you an e-mail with the subject line “You must read this,” which turns out to be a much-forwarded claim that mass marketers are about to run up charges on your cell phone with unwanted sales calls? You can debunk that easily at any of the several websites that specialize in puncturing urban myths, and get authoritative word directly from the Federal Trade Commission itself.

In this chapter, we’ve been stressing that facts are important. We now turn to how to tell which facts are most important, and how to tell the difference between evidence and random anecdotes. Later on we’ll tell you how you can get those facts yourself, using some of the techniques we use every day at FactCheck.org.

Chapter 6

The Great Crow Fallacy

Finding the Best Evidence

TERRY MAPLE WASN’T SURE, BUT HE THOUGHT HE MIGHT HAVE seen a crow using cars to crack walnuts. He had spotted the crow dropping nuts on the pavement one day as he drove through Davis, California. Maple couldn’t know that his curious observation would give rise to a twenty-year legend that would significantly elevate crows’ status on the avian IQ scale. We tell the story here as a cautionary tale to those with a tendency to draw fast conclusions from limited evidence.

Maple, a psychology professor at the University of California–Davis, published an article in 1974 describing the single crow and its behavior. The title was “Do Crows Use Automobiles as Nutcrackers?” Maple couldn’t answer the question, and it wasn’t even clear whether the crow he saw had managed to crack the nut it dropped: “I was, unfortunately, unable to return to the scene for a closer look,” he wrote. The professor correctly called his observation “an anecdote,” meaning an interesting story that suggested crows might use cars to crack walnuts, and that future research might settle the question.

Jump ahead three years, to a November morning in 1977. A biologist named David Grobecker observed a single crow dropping a palm fruit from its beak onto a busy residential street in Long Beach, California. The bird seemed to wait, perched on a lamppost, until a car ran over the fruit and broke it into edible fragments. Then it flew down to eat. This happened twice in the space of about twenty minutes. Grobecker and another biologist, Theodore Pietsch, published an article the following year whose title, “Crows Use Automobiles as Nutcrackers,” suggested they had answered the question posed by Maple. “This is indeed an ingenious adjustment to the intrusion of man’s technology,” the authors concluded.

For nearly twenty years, others cited these two published accounts as evidence of exceptional intelligence in crows. Indeed, some crow fanciers remain convinced—largely on the basis of these two anecdotes—that crows have learned how to use passing cars to crack nuts. But it turns out that although crows are smart birds, they are almost certainly not that smart.

How do we know? Because we now have some real data, not single observations or anecdotes. There is a big difference, as the rest of this story illustrates.

The data come from a study published in The Auk, the journal of the American Ornithologists’ Union, in 1997 by the biologist Daniel Cristol and three colleagues from the University of California. Cristol’s study was based on more than a couple of random observations. He and his colleagues watched crows foraging for walnuts on the streets of Davis for a total of over twenty-five hours spread over fourteen days. Just as they had expected, they saw plenty of crows dropping walnuts on the street. Crows, seagulls, and some other birds often drop food onto hard surfaces to crack it open. An estimated 10,000 crows were roosting nearby, and 150 walnut trees lined the streets where the study was conducted. But did the crows deliberately