Example of a histogram with groups
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You work in an auto factory and are having trouble with variability in the length of the camshafts you use. You want to see if the shafts provided by your two suppliers are comparable, so you measure length for a random sample of 100 shafts from each. Create a histogram to compare the camshaft lengths from the two suppliers.

1    Open the worksheet CAMSHAFT.MTW.

2    Choose Graph > Histogram.

3    Choose With Groups, then click OK.

4    In Graph variables, enter Supp1 Supp2. Click OK.

Graph window output

Interpreting the results

The mean lengths of the camshafts from the two suppliers appear similar. However, there is a great deal more variability in the length of shafts provided by Supplier 2. It appears that Supplier 2 is to blame for your problems with inconsistent camshaft lengths. When comparing distributions with histograms, you might find it easier to panel them. See Examples of editing bars.