You can use the Control Charts from Summary Statistics macro, available from our Macros Library, to create an Xbar chart and either an R or S chart from summary data.
1. Click the link, Control Charts from Summary Statistics Macro, below.
2. To the right of the Control Charts from Summary Statistics description, click Code.
3. Save the page as a macro, called QCSUMMARY.MAC, in your Minitab macros directory (for example C:\Program Files\Minitab 15\English\Macros). For instructions, click "How to save this page as a macro."
4. To run the macro, you can use the Session window or the Command Line Editor.
For example, suppose the subgroup means are in C1, the ranges are in C2, and the subgroup sizes are in C3. In the Session window at the command prompt MTB>, or in the Command Line Editor, type the following. Press Enter after each line:
%QCSUMMARY;
MEAN C1;
RANGE C2;
SIZE C3.
(In the Session window, the command prompt changes to SUBC> after the first line.)
If you have standard deviations in C2, instead of ranges, and you want to create an Bar and an S chart, type the following:
%QCSUMMARY;
MEAN C1;
STDEV C2;
SIZE C3.
If you want to use a single constant for all subgroups, you can enter a constant after MEAN, RANGE, STDEV, or SIZE. For example, if the subgroup means are in C1, the ranges are in C2, and the subgroup size is always 5, type the following:
%QCSUMMARY;
MEAN C1;
RANGE C2;
SIZE 5.
You can also use the optional subcommands TEST and HPROCESS (see below for more details). For example, if the subgroup means are in C1, the ranges are in C2, the subgroup sizes are in C3, you want to use tests 1, 2, and 5, and you want to recalculate the control limits when the value changes in C4, type the following:
%QCSUMMARY;
MEAN C1;
RANGE C2;
SIZE C3;
TEST 1 3 5;
HPROCESS C6.
Note: To display the command prompt, activate the Session window and choose Editor > Enable Commands.
Note: To use the Command Line Editor, choose Edit > Command Line Editor.
After TEST, you can list one or more of the following numbers to perform the corresponding test(s):
1 - One point more than 3 sigmas from center line
2 - Nine points in a row on same side of center line
3 - Six points in a row, all increasing or all decreasing
4 - Fourteen points in a row, alternating up and down
5 - Two out of three points more than 2 sigmas from center line (same side)
6 - Four out of five points more than 1 sigma from center line (same side)
7 - Fifteen points in a row within 1 sigma of center line (either side)
8 - Eight points in a row more than 1 sigma from center line (either side)
HPROCESS allows you to define historical stages in the process data. The control limits and center line are then estimated independently within each stage. Stages are much like groups in other Minitab graph commands. Thus, the HPROCESS column is like a group variable in other graph commands, with one exception -- whenever the value in the column changes, a new stage starts. This works the same way the subgroup column works in the control chart commands.
