Statistical Details for Weighted Moving Average Charts

Control Limits for UWMA Charts

Control limits for UWMA charts are computed for each subgroup i as follows.

where:

w is the span parameter (number of terms in moving average)

ni is the sample size of the ith subgroup

k is the number of standard deviations

Control Limits for EWMA Charts

Control limits for EWMA charts are computed as follows:

where:

r is the EWMA weight parameter (0 < r ≤ 1)

xij is the jth measurement in the ith subgroup, with j = 1, 2, 3,..., ni

ni is the sample size of the ith subgroup

k is the number of standard deviations