StATS: P control chart, answers to on your own exercises (March 7, 2007)

On the web page

you were asked to calculate P charts for the following two data sets:

Worker #2:
60 56 78 60 74 70 70 68 82 76 72 76
68 78 76 68 74 56 74 62 60 70 60 84

Worker #3:
24 32 20 14 32 22 20 26 26 38 30 16
36 32 38 14 26 14 38 20 14 18 22 34

For worker #2, the average of all 24 proportions is 0.6967. The control limits are calculated as

and the control chart is

Notice that the computer rounds these numbers slightly differently, reporting the lower control limit as 0.50 rather than 0.51. Do not worry about these small differences, but the computer's value is slightly more accurate.

There are no points out of control on this chart.

For worker #3, the average proportion is 0.2525. The control limits are calculated as

and the control chart is

Again, the answers diverge slightly because of rounding. There are no points out of control on this chart.

This page was written by Steve Simon while working at Children's Mercy Hospital. Although I do not hold the copyright for this material, I am reproducing it here as a service, as it is no longer available on the Children's Mercy Hospital website. Need more information? I have a page with general help resources. You can also browse for pages similar to this one at Category: Control charts.