Stay Out of Rabbit Holes: On Debunking
n 2012, network scientist and data theorist Samuel Arbesman published a disturbing thesis: What we think of as established knowledge decays over time. According to his book “The Half-Life of Facts,” certain kinds of propositions that may seem bulletproof today will be forgotten by next Tuesday; one’s reality can end up out of date. Take, for example, the story of Popeye and his spinach.
Popeye loved his leafy greens and used them to obtain his super strength, Arbesman’s book explained, because the cartoon’s creators knew that spinach has a lot of iron. Indeed, the character would be a major evangelist for spinach in the 1930s, and it’s said he helped increase the green’s consumption in the U.S. by one-third. But this “fact” about the iron content of spinach was already on the verge of being obsolete, Arbesman said: In 1937, scientists realized that the original measurement of the iron in 100 grams of spinach — 35 milligrams — was off by a factor of 10. That’s because a German chemist named Erich von Wolff had misplaced a decimal point in his notebook back in 1870, and the goof persisted in the literature for more than half a century.
By the time nutritionists caught up with this mistake, the damage had been done. The spinach-iron myth stuck around in spite of new and better knowledge, wrote Arbesman, because “it’s a lot easier to spread the first thing you find, or the fact that sounds correct, than to delve deeply into the literature in search of the correct fact.”
Arbesman was not the first to tell the cautionary tale of the missing decimal point. The same parable of sloppy science, and its dire implications, appeared in a book called “Follies and Fallacies in Medicine,” a classic work of evidence-based skepticism first published in 1989.1 It also appeared in a volume of “Magnificent Mistakes in Mathematics,” a guide to “The Practice of Statistics in the Life Sciences” and an article in an academic journal called “The Consequence of Errors.” And that’s just to name a few.
All these tellings and retellings miss one important fact: The story of the spinach myth is itself apocryphal. It’s true that spinach isn’t really all that useful as a source of iron, and it’s true that people used to think it was. But all the rest is false: No one moved a decimal point in 1870; no mistake in data entry spurred Popeye to devote himself to spinach; no misguided rules of eating were implanted by the sailor strip. The story of the decimal point manages to recapitulate the very error that it means to highlight: a fake fact, but repeated so often (and with such sanctimony) that it takes on the sheen of truth.
In that sense, the story of the lost decimal point represents a special type of viral anecdote or urban legend, one that finds its willing hosts among the doubters, not the credulous. It’s a rumor passed around by skeptics — a myth about myth-busting. Like other Russian dolls of distorted facts, it shows us that, sometimes, the harder that we try to be clear-headed, the deeper we are drawn into the fog.