Percentile

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In descriptive statistics, a percentile is any of the 99 values that divide the sorted data into 100 equal parts, so that each part represents 1/100th (or 1%) of the sample or population.

Thus:

The 1st percentile cuts off lowest 1% of data
The 98th percentile cuts off lowest 98% of data

This function can be found in different office applications. For instance, in Microsoft Excel, the function is percentile(array,k), and this returns the kth percentile.

In more detail the calculation of a percentile may differ from application to application.

One definition is that the pth percentile of n ordered values is obtained by first calculating the rank k = p(n+1)/100, rounded to the nearest integer and then taking the value that corresponds to that rank.<ref>{{cite web |url=http://www.mis.coventry.ac.uk/~nhunt/pottel.pdf |title=Statistical flaws in Excel |last=Pottel |first=Hans |accessdate=2006-03-22}}</ref>

Linked with the percentile function, there is also a weighted percentile, where the percentage in the total weight is counted instead of the total number. In most spreadsheet applications there is no standard function for a weighted percentile.

When ISPs bill "Burstable" Internet bandwidth, the 95th or 98th percentile usually cuts off the top 5% or 2% of bandwidth peaks in each month, and then bills at the nearest rate. In this way infrequent peaks are ignored, and the Customer is charged in a more fair way.

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