Just What Does an EWMA Do? – Mini Paper Taken from the Summer 1995 Newsletter

Abstract: The Exponentially Weighted Moving Average (EWMA) generates a mathematical model of the time series, which may be used to (1) forecast the next value, and (2) monitor the time series for a lack of control. The paper compares the EWMA to a control chart in two ways: first an empirical comparison based upon a set of industrial data is made, and then the theoretical performance of EWMAs and control charts are made using Average Run Length curves. The differences between process monitoring with automatic process control and process improvement using SPC are outlined.

Keywords: Exponentially Weighted Moving Averages (EWMA) - Control charts - Shewhart chart - Average run length (ARL) - Statistical process control - Automatic process control