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Statistical Techniques and 6 Sigma Cpm versus sample size

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Author  Topic: Cpm versus sample size 
student without holiday unregistered 
posted 24 July 2001 12:18 PM
As I read in this forum before the Cpmindex uses every measurement and not only the means of a sample. But when you take samples of different sizes during measuring the Cpmindex 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 ? greetings IP: Logged 
CristiánC Lurker (<10 Posts) Posts: 3 
posted 29 July 2001 11:08 AM
quote:
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 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 
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