Revision Date: 2005-09-19
Problem:
| Several customers have presented us with data in the following general form:
Date Number of days
8/1/2003 12
8/1/2003 11
8/1/2003 9
8/2/2003 8
8/2/2003 10
8/3/2003 11
8/3/2003 9
8/4/2003 8
8/4/2003 10
8/4/2003 7
They want to use this data for an X-bar chart but an X-bar chart requires subgroups of data. A subgroup is two or more numbers (observations) which are used to calculate an average. | |
Solution:
| In this case, subgroups must be created by using multiple rows of data. We have a date we can use for grouping. You might think about this same data set in a different form like this:
8/1/2003 12, 11, 9
8/2/2003 8, 10
8/3/2003 11, 9
8/4/2003 8,10,7
Since the data is not in this handy form, you need to use a CHARTrunner feature called advanced row selection. On the data definition tab, click on the button named advanced row selection.
Unzip the attached file into a temporary folder. Run CHARTrunner and set the working folder to this temporary folder. Study the chart definition and the Excel sheet to see the solution to this problem. Since subgroup size will vary in an unpredictable way, the control limits are adjusted to reflect the changing subgroup size. | |
