The fallacy of “cents” and “ages” (or, Per“cent” vs. Percent“age”, or Damn, that’s a lot of pineapple!)

Dolpicana was already the world’s largest and most efficient network of pineapple plantations in 1990, producing 500,000 tons a year. 20 years later, the company was able to celebrate annual growth of 15 percent!

This is a made-up example of the type of text I often come across while helping authors develop research reports – the kind of statistical claim that compels me to do a little fact-checking. If the above statement were true as written, then Dolpicana would have produced a whopping 8 million tons of pineapple in 2010. As an editor, I would think to myself, “I guess this isn’t an impossible number, but it sounds improbable given Dolpicana’s already-superior standing in 1990. And what is there 8 million tons of anyway?” What’s more likely here is that production in 2010 was 575,000 tons – a 15% increase over production in 1990. That example focused on overall vs. annual growth. Here’s another example that brings in the percent vs. percentage issue:

The company’s market share in January 2010 was a respectable 20% but soared to a staggering 40% by year’s end – growth of 20% in less than a year!

Actually, this company’s market share grew by much more than 20% – it doubled. Its share did, however, grow by 20 percentage points. Percent and percentage points are often incorrectly used interchangeably. The terms sound alike, but the differences are huge.

Among your editor’s tools are a solid understanding of probability and statistics, a calculator, and a red flag that gets raised at the slightest hint of numerical absurdity. We’ll be sure that the results of your research and careful analyses don’t get misconstrued by bad choices in phrasing.

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