Percentage and Percentile
The following paragraph occurred in the denunciation of a certain person in a letter to the editor in my local paper:
He has obstructed the most wholesome and necessary programs which provide for the common good, and has awarded massive financial advantages to a small percentile of the rich.
This erroneous substitution of the word percentile for percentage merits attention. This is not the first time I’ve encountered it.
Some speakers and writers may feel that percentile sounds more “high class” than more ordinary percentage; the word may therefore be in danger of catching on as a genteelism, like “disinterested” for “uninterested.”
A percentage is a part of a whole expressed in hundredths. It can also mean, as the letter writer intended, an indeterminate part of a number.
Merriam-Webster defines percentile as
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
The College Board site explains the use of percentiles this way:
Percentiles compare your scores to those of other students who took the test. Say, for example, your critical reading score is 500. If the national percentile for a score of 500 is 47, then this means you did better than 47 percent of the national group of college-bound seniors.
(NOTE: An NPR score reports comparative rank among test-takers, not necessarily mastery of a subject.)
The only time to use the word percentile is when talking about statistics. For everything else, there’s percentage.