Word Usage: Percent vs. Percentage (and What's a Percentile?)
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Are percent and percentage synonyms? Can I use them interchangeably?
Unfortunately, no. Fortunately, it's easy to learn when you should use percent vs. percentage.
Did you know there was a difference between these two words before reading this article?
See results without votingPercent
A "percent" is always a specific number, amount, or quantity, such as 5 percent or 100 percent.
Usage rules:
- Never spell out the number in front of the word "percent", even if you would normally spell it out. For example, "5 percent" is correct, not "five percent".
- Always use one space between the number and "percent". For example, "5 percent" is correct, "5percent" is incorrect.
- Spell out "percent" as one word, never "per cent" or "per ¢" or "%".
Exceptions to the rules: (pesky, but necessary)
- It's okay to use the symbol "%" in tables and highly technical materials where the term comes up repeatedly.
- Or, if it is mandated in your house style guide.
- Or, if it is used directly in or on a product, such as a user interface, that you are documenting.
Percentage
A percentage is never a specific amount, it is a generalization or trend in specific amounts. For example:
- ...a greater percentage of students...
- ...test results showed higher percentages, sometimes up to 20 percent higher...
- ...we're looking for a lower percentage of...
- ...rates went down by a large percentage...
- ...buy it now before the discount percentages disappear...
Follow the same usage rules as for "percent", above.
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So, then what's a "percentile"?
Percentile, by the way, is also called "centile".
If you have a hundred things--people or pieces of candy, for example--a "percentile" marks the boundary between any two intervals in that group. You can have more or fewer things than 100, you just mathematically make it equal to a fraction of 100 and multiply that number by the number of things you DO have. Some examples will make it clear:
- "My test score is in the 80th percentile"—This means that the score is 80 percent higher than all other scores in the group and that 19% of scores are higher than this one.
- There are 547 pieces of candy in several different colors. To say, "Red is in the 12th percentile of all colors" is to say that 12 percent (12% x 547 = 66 candies) are red and 481 (88% x 547) candies are not red.
Here's how the experts define it:
"the value of the statistical variable that marks the boundary between any two consecutive intervals in a distribution of 100 intervals each containing one percent of the total population -- called also centile."--"percentile." Webster's Third New International Dictionary, Unabridged. Merriam-Webster, 2002. http://unabridged.merriam-webster.com (16 Jan. 2012).
Follow the same usage rules as for "percent", above.
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Thanks, FitnezzJim! Happy hubbing! (I'll try to figure out how to re-word the poll, too.)
Your definition of "percentile" is roughly correct, though poorly articulated and difficult to parse. But both your examples are wrong.
If a score is 80 percent higher than all other scores in a group then it will be the top score -- by a very large margin, and therefore "in the 99th percentile" (we generally do not refer to a "100th percentile").
The second example involves what we call "qualitative (non-numeric) data". When the points of data cannot be ranked against each other on a scale, as with numeric "scores", the term "percentile" is meaningless. In the example you give, it is correct (only) to say that 12% of the candies are red.
Here's how one computes percentile: List (i.e., rank) all your points of data from smallest to largest. Now divide them up into 100 equal-sized groups by placing 99 dividers in appropriate places along the scale. The first group is the 0th percentile; the next group is the 1st percentile, all the way up to the 100th group, which is the 99th percentile. If your score is in the 80th percentile in a class of 100 students with no two scores the same it is higher than 80 other students' scores and lower than 19 others. But you have no information about how much higher or lower you have scored than the others.
What if the number of points is not a multiple of 100, or when you divide them up, some data in the group above a divider have the same value as those below? No matter. There are rules of thumb for these, but the basic idea is "do the obvious thing". Being "in the nth percentile" always means "at least as high as n% of the other points".
"Quartiles" are obtained in a similar fashion by dividing the data into four parts of equal size. The "median" is the point of division between the 49th and 50th percentiles.
Remember, quartiles and percentiles are GROUPS of data (or individuals), which is why we say "in the ... ". On the other hand, the median is only a single value, so we do not say "in the median", but "above", "below" or "at" the median. Above the median you are in the top half of the class; below it you are in the bottom half.
Thanks for setting the record straight, Dr. Craigen! I should have taken more time writing that one out. And, you even added quartiles and the median to the group of math terms frequently mis-used. It's my pet peeve when people don't use technical terms correctly, so I'm literally blushing at my poor description of percentile, and I know better, too. Thanks again! --Laura, B.A. (Physics and Writing)
Not a problem. I didn't mean to publicly embarrass you -- I slip up very easily, and even at 53 years of age I am often shocked my some term or phrase I've been using for years, which turns out to have a significantly different shade of meaning than I had thought all my life. I discovered only recently that I have been using "factoid" slighly wrongly, and therefore saying a few silly things. I had always thought it meant "some minor fact, easily stated" -- a valid, true, fact. But in fact its PRINCIPAL meaning is in reference to a made-up spurious statement presented as "fact". Some dictionaries allow my meaning, but only as a secondary connotation. And I see now that using the term in many situations has reversed my intended meaning. And ... that's a fact.
No problem, Dr. Craigen. I would MUCH rather have correct information published than worry about my own ego (which is tarnished by incorrect information, too). So, again, I thank you for setting me straight--you didn't "publicly embarrass" me, you just helped me get the right information out for other people to use however they need to. We're all wrong sometimes, that's no big deal--unless we don't make it right. :-)
FitnezzJim Level 6 Commenter 4 months ago
I wanted to vote, but didn't because there was no option for 'Not sure how I've used them in the past, but will go back to look'. I may have used them on Hubs here, but will go back and look (and modify as needed). I know I've used the words elsewhere, and will be sure to think conciously about using them properly in the future.
Good write-up, it is clear and well-explained.