Percentages vs. Percentiles: What's the Difference?

Percentages and percentiles are two related but different concepts that are critical to understanding most score reports from pre-employment tests.  Most people are extremely comfortable with the idea of percentages.  In school, all our assignments were graded with percentages. We use them to calculate sales tax.   They’re even on food packaging to express the recommended daily intake of vitamins per portion.  We come across them a lot in our day to day lives.  On the other hand, “percentile” is a similar word that means something very different, and you may not have encountered it before.  Here’s how you can distinguish between the two:

Percentage

Percentages are part of our everyday lives, from calculating how much to tip to determining your bank account’s interest.  In simplest terms, a percentage is a number expressed as a fraction of 100.  It is also uniquely signified with the use of a percent sign (%).  A simple example might be a candidate’s score on a pre-employment test. Take this example:

A candidate takes a test made up of 40 questions and answers 34 of them correctly.  Her percentage of correct answers, or score, is the number of correct answers divided by the total number of questions, multiplied by 100.

So,

35 ÷ 40 = 0.85

0.85 × 100 = 85

The candidate got 85% of the questions on the test correct.

This may seem like a review, but having a firm grasp on how percentages work is integral to understanding percentiles.

Percentile

Though they sound similar, the concept of percentiles is completely different from percentages.  Percentiles express all the observations of a given occurrence, below a certain percentage of that occurrence. So, what does that even mean? While percentages give you an indication of how well an individual person performed on a test, percentiles give you an indication of how well that person did compared to others. It’s a more complicated idea than a percentage and might be best illustrated by looking at all of the candidates’ scores on the same test we were talking about above:

Let’s look at the scores of all the candidates who took the pre-employment test that had 40 questions.  The distribution of scores ends up looking something like this:

Image

The height of each bar represents the number of people who received that particular score. So, more people received a score of 34 than a score of 20.

If the same candidate answered 34 questions correctly, according to the distribution of all the scores in the group, she scored better than 60% of the other applicants.  This is her percentile rank. To be clear, she did not get a 60% on the assessment.  Her 60^th percentile rank is an expression of how the candidate did relative to everyone who took the test, not her individual score.  In other words, a percentile rank is a way of rank ordering people compared to others in a sample. In the example above, a raw score of 34 means that she answered 85% of the questions correctly (percentage) AND scored higher than 60% of everyone else who took the test (percentile).

For some, there could be an initial shock if they see that their percentile rank for an assessment is at or near the 60^th percentile.  You might immediately assume that you’ve somehow failed since we’re so used to being graded and measured in terms of percentage.  In reality, a percentile rank of 60 is actually an above average score.  It isn’t directly related to how many questions someone answered correctly, but where their score fits among every other test takers’ scores. On this same test, someone who answered 30 questions correctly would have gotten 75% correct (percentage) and fall into the 31st percentile. The percentile just depends on how everyone else scored.

There’s a reason that percentile rankings are often more useful for interpreting test results. If you aren’t familiar with a test, knowing that someone got 75% of the questions correct doesn’t tell you if they scored well or not since you don’t know how hard the questions are or what the average score is. However, if someone scores within the 75th percentile, you know that they did well on the test because they scored better than ¾ of the people who have taken it.

Understanding the difference between percentages and percentiles ultimately can help you interpret pre-employment test results so you can make the most informed decision on which candidates you should invite to the next step of the hiring process.