Percentages and Ratios: How Are They Different?

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One of the more familiar types of statistics we have all used at some point or another is the percentage. At the very least, we have all seen percentages used in journal or news articles as evidence to support argument. For instance, this article on the fires in the Amazon rainforest in South America lists a few facts like how 6 percent of the planet’s oxygen comes from the rainforest.

This percentage makes sense at face value. But what about when you bring in other statistics that are similar to percentages like ratios? For instance, another statistics cited in the same PBS article is that a ratio of 1 in 10 known species live in the Amazon. This also makes sense and is equally informative. But what if I asked you to explain the difference between percentages and ratios?

The breakdown

Let’s start with why these two statistics are helpful. Percentages and ratios help you understand the relationship between a slice to the whole. That is, they are proportional measures. They help you answer questions like, “Looking at the big picture, how important is this piece of the picture?” or “How does this amount compare to these other amounts?” Percentages and ratios summarize how one number relates to another, which helps us quickly understand the significance and relationship between the two numbers.

So what is the difference between percentages and ratios and how should they be used? According to Data Literacy by David Herzog, the definitions are quite straightforward:

PercentageRatio
How is it different than the other?Compares a portion of a total to the totalCompares the difference between numbers from different groups
How should it be used?Use when you want to assess how significant a portion or amount is to an established totalUse when you want to understand and compare the relationship between two groups
Here’s an exampleWomen make up 25% of the U.S. Senate in 2019.For every 4 male U.S. Senators, there is 1 female U.S. Senator in 2019.

You’re measuring the number of women in the U.S. Senate in the percentage and ratio examples. Wouldn’t you only use either a percentage or ratio to measure and compare the number of women in the Senate?

The percentage and ratio examples are comparing the number of women to two different groups: the percentage example is comparing the number of women to the total Senate population and the ratio example is comparing the number of women to the number of men in the Senate. In the percentage example we are highlighting the fact that females comprise a not insignificant chunk of the Senate, but in the ratio example we are highlighting the fact that the number of male Senators significantly outnumber the number of female Senators. As you can tell, the angle of the story is different between the percentage and ratio examples!

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