An EWMA chart is used to detect out-of-control situations quickly. EWMA charts incorporate information from all previous subgroups, weighting the information from the closes subgroup with a higher weight.
The weight can have a value between 0 and 1.For individual observations, the individual values will be used in place of subgroup means in the calculations.
The EWMA for subgroup 0 will be set to the mean of the data under consideration.
The following is the equation for computing the Exponentially Weighted Moving Average (EWMA).
Note: The default weight used is 0.2.
W = weight
= Mean of Subgroup i
Central Line, CL =
Upper Control Limit
Lower Control Limit
Moving average charts overview.