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.

Data Available

W = weight

= Mean of Subgroup i

Central Line

Central Line, CL =

Upper Control Limit

Lower Control Limit

Moving average charts overview. |