Sample Size for Second Level Pareto
- February 20, 2018 at 8:46 pm #55943
On a production line working a around 6000 pcs per hour, all three shift production, the average rejection is around 5% ( data from 30 days production) . The automatic detection system gives the first level pareto for the cause of these rejects. Cause 1 is around 40% and cause 2 is around 25%. For the next level analysis each part is to be opened to know the reasons for the reject under a broader category. How to calculate the sample size and period of analysis for the next level reject analysis? That is if we want to be sure that Cause 1 sub categorized into x1,x2,x3,x4, to make a right pareto how many samples should be opened and what frequency. ( with respect to margin of errors and statistical significance)February 21, 2018 at 5:58 am #202289
For a control chart, we like to have 100 samples before calculating control limits. But you don’t always need to go that far. There is a concept I’ve heard Jay Arthur call The Dirty Thirty. If you can go back to your original 30 days worth of data, that would be great. If you can get 30 shifts worth of data (10 days, 3 shifts) that would be pretty good too.February 21, 2018 at 5:05 pm #202295
Ummmm, why not address the top defect. Don’t complicate it.
My two cents.February 27, 2018 at 8:10 pm #202331
Hi Chris @cseider, thanks for a quick response. Trying to address the top defect only but there are 6~7 possible causes for this top defect and would like to prioritize on which cause/s to attack first. Practically it would require deeper investigation on each failed item ( time and resources on one hand) but s required to be sure on the most significant ones and also to know if there are differences between shifts ( multi-vari). So the question is the sample size for this next level pareto.February 28, 2018 at 9:42 am #202332
My approach is simple…work on the top 2nd level pareto cause and confirm if defect rate drops after you’ve solved the root cause. I’d less worry about whether you have enough data and use what you have. I’m excited you know to get to a 2nd level pareto to find where to tackle initially.March 2, 2018 at 3:39 am #202335
Get secondl level of pareto
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