Each plotted point, , represents the mean of the observations for subgroup,
.
Term | Description |
---|---|
xij | jth observation in the ith subgroup |
ni | number of observations in subgroup i |
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:
Term | Description |
---|---|
![]() | sum of all individual observations |
![]() | total number of observations |
The value of the lower control limit for each subgroup, i, is calculated as follows:
The value of the upper control limit for each subgroup, i, is calculated as follows:
Term | Description |
---|---|
μ | process mean |
k | parameter for Test 1 (The default is 3.) |
σ | process standard deviation |
ni | number of observations in subgroup i |