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This thread is carried over and continued in the Current Elsmar Cove Forums 
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This thread is carried over and continued in the Current Elsmar Cove Forums
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The New Elsmar Cove Forums
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 The New Elsmar Cove Forums
 Statistical Techniques and 6 Sigma
 Statistically Valid Sampling Plans
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| Author | Topic: Statistically Valid Sampling Plans |
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Dawn Forum Contributor Posts: 245 |
posted 02 October 1999 07:27 PM
   
QS Auditor wants to see proof that 3 piece smaples for run charts is a statistically valid number. I have researched and pretty much proved he's right - its not. Employees feel five piece checks are too cumbersome. What to do? Thanks for any help-Dawn IP: Logged |
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Batman Forum Contributor Posts: 111 |
posted 03 October 1999 11:00 AM
Hi Dawn! A subgroup of three may be right for you, five may be better, one may be correct also. Look at your process and determine the correct sample size and frequency. When we start a process, we take many samples in a short time, identify the assignable causes, remove or reduce them, start the process again, take less frequent samples, assess control, and so on, until the assignable causes are eliminated (or at least identified) and we know how long we can run until variation is expected to show up, thus samples are taken prior to this, for possible adjustment. You can do this for present processes also, if needed. I find that frequency has more to do with "control" than the sample size, except with multi-cavity tools. IP: Logged |
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Don Winton Forum Contributor Posts: 498 |
posted 03 October 1999 12:08 PM
Dawn, Batman pretty much sums it up. Do not think of sample size in terms of the MIL-STD-105 mentality. Size and frequency are the keys. Show the assessor your justification in statistical terms where n=3 is valid. Regards, ------------------ Check Out dWizard's Lair: IP: Logged |
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