EWMA Control Chart Options
Options | EWMA Control Chart Options
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This dialog is used to specify options for the exponentially weighted moving average (EWMA) control chart.
Baseline Samples
This is the number of baseline or reference samples used to construct the control chart. The 1989 guidance recommends that at least 8 baseline samples known to be uncontaminated be available to construct the baseline mean and standard deviation. This value is used in intra-well comparisons only.
If the value entered here is positive, the value entered is the number of baseline samples. For a data set with 15 samples from the specified well, if a value of 8 is entered, the first 8 samples will be used to construct the baseline mean and standard deviation. The remaining seven samples will be plotted on the control chart and compared to background.
If the value enter here is negative, the magnitude of this value is the number of the most recent samples plotted on the control chart. For a data set with 15 samples from the specified well, if a value of -7 is entered, the first 15-7=8 samples will be used to construct the baseline mean and standard deviation. The remaining seven samples will be plotted on the control chart and compared to background.
Lambda (l)
0 < l £ 1 is a constant, typically between 0.05 and 0.25 for quality control use. Higher values will reduce the ability to detect increases. Lower values of l increase the weights of historical values. This may decrease susceptibility to anomalously elevated concentrations.
L Value
L is the multiple of the standard deviation for the control limit.
Group Size
This is the number of values to be averaged and compared to the control limit. For a value of 1, each individual concentration is compared to the control limit.
Circle Exceedances
If this box is checked, data points exceeding the control limit will be drawn with a circle. This helps to distinguish points showing exceedance for those unfamiliar with control chart interpretation.
Data Connection Line
The style of the line that connects data points on the control chart.
Chart Limit Connection Line
The style of the line that connects points of the control chart limit.