Population vs Sample

The Average is 20 millimeters, but individually they vary from 19.10mm to 20.90mm. This is OK with our customers because their specification calls for and Average of 20mm with a Tolerance of +/-1.5mm. That means they will accept anything between 18.5 and

Our problem is to keep the widget cutting machines at the center of 20.0mm and to not let individuals vary (disperse) more than they did in this lot.

All of the gadgets we measured were made at one time (the same Run) on the same machine by the same operator and from the same material lot. Because of all these things being the same, we can be quite sure that the Pattern of their Variation will almost e

We would also know that the greatest Individual Variations will be quite close to +/-3 s. This is a Spread of 6 Standard Deviations.

The difference between the Longest (20.9mm) and the Shortest (19.1mm) is 1.80mm. One sixth of 1.80 is 0.3. So…. The standard deviation is 0.3mm.

Since we measured every widget, we measured the entire Population. We can do the same thing with a Sample.

Previous slide

Next slide

Back to first slide

View graphic version

The Juran Trilogy	The Deming PDCA Cycle	QMS Implementation	FMEA Information	APQP Information
Auditing Information	8-D Problem Solving	Statistics	Error Proofing (Poka Yoke)	Brainstorming
Identifying Waste	Pull Systems	Lead Time Reduction	Planned Maintenance	Quick Setup
Discovering Change	Process Capability - Cp vs. Cpk	Histogram Animation	Process Loop Animation	Taguchi Loss Function
		Fishbone / Cause and Effects Animation

All Y'All Come Back Now, Y' Hear?

Forums provided and maintained by Marc Timothy Smith

FAIR USE and CORRECTNESS NOTICE: This site contains copyrighted material the use of which has not always been specifically authorized by the copyright owner. We are making such material available in our efforts to advance understanding of environmental, political, human rights, economic, democracy, scientific, and social justice issues, etc. We believe this constitutes a 'fair use' of any such copyrighted material as provided for in section 107 of the US Copyright Law. In accordance with Title 17 U.S.C. Section 107, the material on this site is distributed without profit to those who have expressed a prior interest in receiving the included information for research and educational purposes. For more information go to: http://www.law.cornell.edu/uscode/17/ If you wish to use copyrighted material from this site for purposes of your own that go beyond 'fair use', you must obtain permission from the copyright owner. In addition, I do not guarantee the correctness of the content. The risk of using content from the Elsmar Cove web site and forums remains with the user.