Exponentially weighted moving average charts are useful for finding small shifts in the mean in a process. Here, we will use the EWMA chart to study the temperature data from the Oxford weather station. We will look at the results for January to investigate whether we have a change in mean monthly maximum and minimum temperatures across the data from 1853.

Both EWMA and CUSUM charts are useful in scenarios where we cannot collect rational subgroups for an Xbar chart. As with the temperature data from the Oxford weather station, we have a mean maximum temperature for a month; there are no subgroups. We can use the EWMA to be more sensitive to smaller scale shifts than the I-MR chart.

We will start by splitting the worksheet into months, selecting the worksheet for January, and then plotting the EWMA for maximum and minimum temperatures.