Percentiles divide data into 100 equal parts. They are commonly used for providing a relative standing of an event or person in a population. You can also calculate percentiles for grouped data. One type of percentile calculation is decile. Deciles are a percentile taken in tens. The first decile is equivalent to the 10th percentile and the second decile is the 20th percentile, and so forth. This is commonly used in investments or in education with testing.

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Determine if you want the lowest decile or the highest decile, that is, are you looking for the highest 10 percent or the lowest 10 percent?

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Sort your data from highest to lowest.

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Multiply the total number of data points by 0.10 (10 percent) for the number of data points in the top decile. For example, if you have 10 data points then 10 x 0.10 equals 1. This means that your highest (or lowest) number represents the numbers in your decile.