Methods and formulas for Xbar Chart

Select the method or formula of your choice.

Plotted points

Each plotted point, , represents the mean of the observations for subgroup, .

Notation

TermDescription
xijjth observation in the ith subgroup
ninumber of observations in subgroup i

Center line

The center line represents the process mean (). If you do not specify a historical value, then Minitab uses the average from your data, , which is calculated as follows:

Notation

TermDescription
sum of all individual observations
total number of observations

Control limits

Lower control limit (LCL)

The value of the lower control limit for each subgroup, i, is calculated as follows:

Upper control limit (UCL)

The value of the upper control limit for each subgroup, i, is calculated as follows:

Notation

TermDescription
μprocess mean
kparameter for Test 1 (The default is 3.)
σprocess standard deviation
ninumber of observations in subgroup i
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