How to Calculate a Quintile

By Kevin Lee
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Calculating a quintile can help you zero in on interesting and informative patterns in a data set. A quintile is a group of numbers that represents 20 percent of the values that reside in a larger set. A company, for example, may calculate quintiles to discover how much its lowest selling items contribute to the company's total sales.The government, on the other hand, might calculate quintiles to discover how income is distributed between different five different age groups.

Step 1

Sort a list of at least five numbers in ascending order and place them in a column, as seen in the following example:

100 500 700 1,200 1,300 20,000 40,000 55,000 58,000 61,000

Step 2

Calculate the sum of the values in your data set. The sum of the values in the above example is 237,800.

Step 3

Divide the numbers into fifths by drawing lines that separate the quintiles. If you perform this task using the sample data, you’ll see the following:

100 500

700 1,200

1,300 20,000

40,000 55,000

58,000 61,000

The numbers above each line represent a quintile. In the above example, the numbers in the second quintile are 700 and 1,200. The values 58,000 and 61,000 make up the fifth quintile.

Step 4

Divide the fifth quintile’s sum by the data-set sum and multiply the result by 100, as shown in the following example:

(119,000 / 237,800) * 100 = 50.04.

The result represents the percentage that the fifth quintile contributes to the data set’s total value. In this example, the fifth quintile accounts for over 50 percent of the data set’s total value.

Step 5

Repeat this calculation to determine the contribution percentages of the other four percentiles.

About the Author

After majoring in physics, Kevin Lee began writing professionally in 1989 when, as a software developer, he also created technical articles for the Johnson Space Center. Today this urban Texas cowboy continues to crank out high-quality software as well as non-technical articles covering a multitude of diverse topics ranging from gaming to current affairs.