5. Results
An example of the application of the EWMA control chart is shown in Fig. 5. While the normalized residuals were noisy, the EWMA clearly shows the appearance of a variation. Before the variation appeared, the EWMA oscillated around the center line (zero). The shift here appeared in September and the detection occurred at the end of October. For this example, the shift was a 10% annual underperformance, with λ = 0.1. In this case, the presence of the change in behavior by the WTG was obvious, but attempting to find the moment when the shift became clearly identifiable would have been hazardous without the use of a control chart.