Quartiles break down data into four groups based on the results. The upper quartile equals the highest 25 percent of scores. For example, on a standardized test, the upper quartile would be the 25 percent of test takers who earned the highest scores on the test. If you need to place in the top 25 percent, such as if you want to attend a college that only accepts students in the top 25 percent, you need to know how to find the top quartile.
Things You'll Need
Add 1 to the number of items in your data set. For example, if your data set has 23 items, add 1 to 23 to get 24.
Multiply the result by 3/4 to find the item in your data set that equals the upper quartile. In this example multiply 24 by 3/4 to get 18.
Identify the item or items the number corresponds to on a list of your data points organized from smallest to largest. If the number in Step 2 is a decimal, find the value of the point above and below. For example, if the Step 2 result equals 15.5, find the 15th and 16th number. In the current example, find the 18th number to find the upper quartile.
Take the average of the two surrounding items if you get a decimal for Step 2. For example, if you get 15.5, take the average of the 15th and 16th smallest numbers to find the upper quartile.
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