The Elsmar Cove Business Standards Discussion Forums More Free Files Forum Discussion Thread Post Attachments Listing Elsmar Cove Discussion Forums Main Page
Welcome to what was The Original Cayman Cove Forums!
This thread is carried over and continued in the Current Elsmar Cove Forums

Search the Elsmar Cove!

Wooden Line
This is a "Frozen" Legacy Forum.
Most links on this page do NOT work.
Discussions since 2001 are HERE

Owl Line

The New Elsmar Cove Forums   The New Elsmar Cove ForumsThe Elsmar Cove Forums
  Statistical Techniques and 6 Sigma
  Cpm versus sample size

Post New Topic  Post A Reply
profile | register | preferences | faq

UBBFriend: Email This Page to Someone! next newest topic | next oldest topic
Author Topic:   Cpm versus sample size
student without holiday
unregistered
posted 24 July 2001 12:18 PM           Edit/Delete Message   Reply w/Quote
As I read in this forum before the Cpm-index uses every measurement and not only the means of a sample.
But when you take samples of different sizes during measuring the Cpm-index gets more influenced by the values of the larger sample sizes.

For exemple: someone working in a laboratory has to weigh fluids. He takes sample sizes of 4. This person is a bit awkward and now and then drops a bottle with fluid. So the sample size drops to 3. At the end of the measurements he wants to know the Cpm of the weight. If he uses al the measurements the samples of 4 have more effect than the samples of 3. What should he do ?
When he uses an overall sample size of 3 he has made to much measurements and he wants to use them all. (because for example he had used an expensive method for weighing)

greetings

IP: Logged

CristiánC
Lurker (<10 Posts)

Posts: 3
From:Belo Horizonte, Minas Gerais, Brazil
Registered: Jul 2001

posted 29 July 2001 11:08 AM     Click Here to See the Profile for CristiánC   Click Here to Email CristiánC     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by student without holiday:
As I read in this forum before the Cpm-index uses every measurement and not only the means of a sample.
But when you take samples of different sizes during measuring the Cpm-index gets more influenced by the values of the larger sample sizes.

For exemple: someone working in a laboratory has to weigh fluids. He takes sample sizes of 4. This person is a bit awkward and now and then drops a bottle with fluid. So the sample size drops to 3. At the end of the measurements he wants to know the Cpm of the weight. If he uses al the measurements the samples of 4 have more effect than the samples of 3. What should he do ?
When he uses an overall sample size of 3 he has made to much measurements and he wants to use them all. (because for example he had used an expensive method for weighing)

greetings



Let me tell you what I think:

Before calculating Cpm index, a Control Chart must be created from the data collected. If the process is stable (the weighing process variation is under common cause of variation only), then it is apropriate to think about capability indices.

Each and every datum belongs to the population depicted in the Control Chart (remember: only common causes), therefore
the size of the sample has NO "effect" in the sense you posted.

My sugestion (strictly referredn to the problem that you stated) is that you do not need to worry about variations in the size of the samples for Cpm calculations. Such variation must be taken into account when constructing control charts.

Hope this helps.


IP: Logged

All times are Eastern Standard Time (USA)

next newest topic | next oldest topic

Administrative Options: Close Topic | Archive/Move | Delete Topic
Post New Topic  Post A Reply
Hop to:

Contact Marc Smith | The Elsmar Cove Home Page

Please Visit the new Elsmar Cove Forums! All these threads are there and much more!

Main Site Search
Y'All Come Back Now, Ya Hear?
Powered by FreeBSD!Made With A Mac!Powered by Apache!