In today’s Wall Street Journal, one of the editorials makes the following statement:

Arizona got into this crisis because during the boom years–2003 to 2007–then-Governor Janet Napolitano, a Democrat, and Republicans in the legislature let spending climb by more than 100% to $10 billion from $6.6 billion.

Of course, the increase was 52%, which is distinctly less than 100%.

But how did the Journal’s editors make this mistake? I think it’s because they’ve succumbed to the incorrect modern usage in discussing increases. Here’s an example:

GDP in a poor country rises from $10 billion to $40 billion. The modern usage is that it “rose fourfold.” But it didn’t. It rose threefold. When I’ve made this point to my students, I’ve pointed out that when a number rises from 50 to 90, by the modern usage one would say that it rose 1.8 fold. But it didn’t. It rose 0.8 fold.

I was wondering when I would first see someone make the error that arises from using the modern usage consistently. I just did.