Example of a boxplot with multiple y's and groups
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Your company makes plastic pipes and you are concerned about the consistency of the diameters. You measure ten pipes a week for three weeks from each machine. Create a boxplot to examine the distributions.

1    Open the worksheet PIPE.MTW.

2    Choose Graph > Boxplot.

3    Under Multiple Y's, choose With Groups. Click OK.

4    In Graph variables, enter 'Week 1'  'Week 2'  'Week 3'.

5    In Categorical variables for grouping (1-3, outermost first), enter Machine.

6    Under Scale Level for Graph Variables, choose Graph variables displayed innermost on scale. Click OK.

Graph window output

Interpreting the results

The boxplot shows:

·     For machine 1, the median diameter and variability appear to increase each week.

·     For machine 2, the median diameter and variability appear to be more stable across weeks.

You may want to perform statistical analyses, such as balanced MANOVA, to further examine the relationship between factors.