Percentages are ubiquitous, and not just in election season. But they remain slightly abstract—a concept used to describe something else. Therefore, we often get them wrong.
If you want to impress your boss or client as a copyeditor, go through and check all the percentages. It won’t be long before you find an error. In some documents, you might find a mistake in one out of five examples. That’s 20 percent.
To edit percentages, first understand them. The concept of percent predates our Arabic numbering system. We have long divided wholes into fractions, and a hundredth of something is the same as a percent—literally “for each hundred.” If you pay a tax of every hundredth basket of dates from your orchard, you are dealing with a percentage. Though based on 100, the tax can be calculated whether you fill 40 baskets or 270.
We can divide any size whole into fractions, as we do with money: half-dollars and quarters are half a dollar or a quarter of a dollar. We once had bits, which were an eighth of a dollar, worth 12.5 cents. A Spanish dollar was eight reales, or “pieces of eight.” An English shilling was a twentieth of a pound sterling.
Dividing by hundredths keeps our fractions to a base 10 system, allowing decimal representation and ease of calculation. It allows us to compare proportions and growth or depreciation under a common denominator (100).
It doesn’t matter if we have 25 apples and 20 oranges, we can make a direct comparison by pretending we have 100 of each. So if we have five bad apples and four bad oranges, our rate of bad fruit in each category is 20 percent.
This is something we started learning in elementary school. But that was a long time ago, and it helps us as editors to remember what percentages are doing: providing a standardized basis for comparison.
Once we are aware of this, we are more aware when comparisons don’t fit.
Some indications a percentage might need closer attention:
- A positive quantity decreasing by more than 100 percent (once it’s gone it’s gone, right?).
- Giving more than 100 percent. It sounds good give 110 percent, but once you give all you have, there is no more to give. Percentages can go over 100 of some previous baseline, but if we’re dealing with a portion of the whole, 100 percent is the limit.
- Unlikely percentages. It’s common in figuring percentages to forget to move the decimal as part of a calculation, so quantities might be expressed as 0.4 percent instead of 40 percent—not a mistake you want to make when reporting a company’s growth rate, for example.
If you see any of these, pause and make sure you understand what is being presented. But, really, a percentage of any kind is a red flag. Stop and do the math. You may be surprised at how often you make a critical save.