How to calculate Percentile value?

In this blog post, we will see about most fundamental stuff in Performance Testing, how to calculate percentile value? First, let us see about percentile value.

What is Percentile Value?

Percentile value is a measure of statistical distribution of the data. The median is the middle value. The median is the value for which 50 per cent of the values were bigger, and 50 per cent smaller. But 90th percentile gives you the value for which 90 per cent of the data points are smaller and 10% are bigger.

90 percentile is considered as a thumb rule in performance testing for result analysis and benchmarking. Most of the performance testing rule sets the 90 percentile value.

How to calculate 90 percentile value?

Easiest way to calculate 90 percentile is as below. Consider you have following ten data, 15, 63, 78, 12, 56, 74, 52, 79, 90, and 46.

Arrange above numbers in ascending order, i.e. 12, 15, 46, 52, 56, 63, 74, 78, 79 and 90. Ninth value i.e. 79 is the 90 percentile value. If you use Microsoft Excel, use =PERCENTILE(array,k) where k is the percentile value you want to calculate, for 90 percentile, k value will be 0.9. Similarly you can calculate for other values 10th percentile, 50th percentile, or any values.

For the above mentioned series, 90 percentile value is 80.1 in Microsoft Excel. Below is the sample Percentile Calculator to find the Percentile Rank (PR) of students.

Happy Testing!

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Image Courtesy: Fotofolia via Microsoft Clipart

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