Creating a Moving Range chart

A Moving Range (mR) chart is a way of monitoring variation to try and work out if a system is varying unexpectedly.

The range is simply calculated as the absolute difference between one data point and the previous one. We then calculate an average—usually over a specific subset of the data—of these values and apply a statistical constant (3.267 - D4 anti-biasing constant for a subgroup size of n=2). The great thing about these constants is that you don't need to understand them or how they are calculated; just that they exist.

In this recipe, we are going to use the same set of rainfall data as the previous recipe, Creating a Statistical Control Chart using Standard Deviation, to see how the rainfall data for Heathrow varies over time. We will use a 30-year period as our reference for what "Average" means (the UK Met office uses 1961-1990).

Getting ready

Load the data from the UK Met Office website as outlined in the previous recipe, Creating a statistical control...