I complain periodically about reporters who make boneheaded arithmetic mistakes—the kinds of errors that are off by a factor of 10 or 100 and should have set off instant alarms. But Felix Salmon points out today that it's also easy to make the opposite kind of error: insisting on numerical accuracy that simply doesn't exist and doesn't matter. The issue at hand is the Norwegian guy who bought $25 worth of bitcoins in 2009, forgot about them, and recently discovered that they were worth $850,000. Sweet! But wait. Was it really $25? Or was it $22? Or $27? Anthony DeRosa was unhappy that different news accounts provided different numbers, but Salmon explains what happened:
It turns out that the reason for the disparity is very simple: the dollar-krone exchange rate fluctuated quite a lot in 2009, and it was unclear exactly when the bitcoins were purchased, so no one knows exactly how much the coins were worth, in dollar terms, when purchased. They might have been worth $22, or they might have been worth $27. Really, it doesn’t make any difference: the man made a profit of well over $850,000 whatever his initial investment was.
But there’s a superficial exactness to numbers that doesn’t exist in words, and so people have a tendency to believe that all numbers are much more precise than in fact they are. If the Labor Department releases a report saying that payrolls rose by 148,000 in September, then a reporter who said that payrolls rose by 150,000 would be considered to have her facts wrong — even though the headline number is only accurate to within 100,000 people either way. The actual number of new jobs could easily be anywhere between 44,000 and 252,000 — and indeed there’s a 5% chance that it’s outside even that large range. But because everybody insists on one hard number, one hard number is what they get.
One of the most important skills in financial journalism is numeracy — having a basic feel for numbers. In this case, the reporters covering the story got the numbers right: they should be applauded for that, rather than having brickbats thrown at them.
Yep. In general, reporters should be more careful with numbers, but ironically, that sometimes means being less exact. Some numbers just aren't precise, and we'd all be better off if we accepted it. Pretending to a precision that doesn't exist is as bad as tossing out a sloppy estimate when a few minutes of work would provide you with the real answer.