2. Walter Shewhart ([1931] 1980) presented the following data in his classic Economic Control of Quality of Manufactured Product . Create a p chart for each machine. Does either of the two machines show evidence of special cause variation?

298 Chapter : Statistical Process Control for Monitoring Failure Rates MACHINE A MACHINE A MACHINE B MACHINE B Month Defective Inspected Defective Inspected Jan 4 527 1 169 Feb 5 610 3 99 Mar 5 428 1 208 Apr 2 400 1 196 May 15 498 1 132 Jun 3 500 1 89 Jul 3 395 1 167 Aug 2 393 2 200 Sep 3 625 1 171 Oct 13 465 1 122 Nov 5 446 3 107 Dec 3 510 1 132 Average 5.25 483.08 1.42 149.33