Example of an interval plot with multiple y's
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Your company makes plastic pipes, and you are concerned about the consistency of their diameters. You measure ten pipes each week for three weeks, then create an interval plot to examine the distributions.

1    Open the worksheet PIPE.MTW.

2    Choose Graph > Interval Plot or Stat > ANOVA > Interval Plot.

3    Under Multiple Y's, choose Simple. Click OK.

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

Graph window output

Interpreting the results

To see the mean, hover your cursor over the mean symbol. To see confidence interval information (estimate, interval, and N), hover your cursor over the interval bar. Mean diameter increases along with variability over time:

·     The mean for week 1 is 5.019 and the confidence interval extends from 4.62777 to 5.41023.

·     The mean for week 2 is 5.474 and the confidence interval extends from 5.04142 to 5.90658.

·     The mean for week 3 is 6.029 and the confidence interval extends from 5.07682 to 6.98118.