Cumulative percentiles

See also: Statistical descriptions of model outputs, Presenting results introduction

These are values below which a specified percent of the generated data for an output fall.  Standard notation is for the Pth percentile is xP e.g. x75 is the value we estimate from the model to have a 75% probability of being below.

Differences between cumulative percentiles are often used as a measure of the variable's range e.g. x95 - x05 would include the middle 90% of the possible output values and x80 - x20 would include the middle 60% of the possible values of the output. x25, x50 and x75 are sometimes referred to as the quartiles.

The median is the 50th percentile and a stable measure of location. The easiest way to illustrate and present cumulative percentiles is to quote the most interesting percentiles in combination with showing them on a cumulative distribution plot.

Read on: Histogram plots

 

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