Boris, there are lots of ways to use different statistically calculated numbers. I am suspicious, nonetheless, that your concept of a plant wide goal for Cpk, either as a point estimate or as a confidence interval, will not let you reach the larger goal you seek.
One can manipulate the math to show that an SPC chart control limits are mathematically equivalent to a Student 't' test. the interpretation of certain terms is not identical, exactly, but who cares? (slap your face, Jay.) the Cp and Cpk can be mathematically adjusted to show the math equivalence. Without going into the details, I believe you can show that The Cpk, CI, and 't' values are closely related. use of point estimates of Cp and Cpk as yardsticks or standards or goals tends to ignore the great sensitivity of the values to variations in the standard deviation. Translation: you would be much better off to use archival documentary data which comes from 50-100 measurements to get decent estimates of the standard deviation. This leads to questions of process variability and product variability. In turn, these variability's will lead (eventually) to a question of customer needs, as interpreted by (engineering, marketing, CEO, whoever). Finally all this number pushing gets down to the real issues! Not every dimension can be easily or precisely measured. Not every dimension needs the same Cpk. So much for plant wide values. I recommend you put your key focus on the issues that really count - customer requirements, as interpreted. Let these determine production requirements. Cheers, Jay Boris wrote: > Hi, Do anyone there have an experience to set organizational (plant) > Cpk goals using Confidence Interval and/or hypothesis testing? > > Most places use just point estimates for Cpk but in the liturature > (like classic Montgomery SPC book) confidence interval approach is > described. > > I'd like to hear about such Cpk assessment system, how does it work in > practice. > > Boris. > > ================================================================= > Instructions for joining and leaving this list, remarks about the > problem of INAPPROPRIATE MESSAGES, and archives are available at > http://jse.stat.ncsu.edu/ > ================================================================= -- Jay Warner Principal Scientist Warner Consulting, Inc. 4444 North Green Bay Road Racine, WI 53404-1216 USA Ph: (262) 634-9100 FAX: (262) 681-1133 email: [EMAIL PROTECTED] web: http://www.a2q.com The A2Q Method (tm) -- What do you want to improve today? ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at http://jse.stat.ncsu.edu/ =================================================================