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15th June 2015, 18:06  #61  
Senior  BHPian Join Date: Dec 2008 Location: New Delhi
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 Re: Are you Six Sigma certified? Quote:
For the project being submitted by you, certain institutions ask for a proof on company letterhead that you actually led the project on your own along with the project presentation. Some like ISI don't care about it and would just want you to submit the story in a word document, no company letterhead or anything. After all, its all business, in case institutions get too fussy about evaluating whether a project is genuine or not then they end up losing customers. If you would only like a 'SSGB Certified' stamp on your resume then ISI is cheap and best. In case you would like after sales support (with their forums etc.) then private institutions are good. ISI training is crappy while pvt institutions (almost all of them) would give you decent material along with ok training on concepts, usage of Minitab etc. Mind you, ISI doesn't even touch Minitab in their curriculum while no pvt institution would provide training without Minitab. So depending on your objective you'd have to decide. Let me also say that I was approached by a somewhat reputed institution to provide GB trainings on my free days and the guy who interviewed me didn't know half of the subject himself. He was an MBB.  

15th June 2015, 18:15  #62  
BHPian Join Date: Sep 2012 Location: Bombay
Posts: 378
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 Re: Are you Six Sigma certified? Quote:
That pretty much sums up the situation in the industry today Will keep this thread posted on what we decide. Regards Dieseltuned  
2nd April 2018, 16:23  #63 
TeamBHP Support  Re: Are you Six Sigma certified? I am trying to get a mathematical understanding of six sigma. But I am a bit confused about the possible ±1.5σ shift in mean. Let's say I am making 1 meter tall walking sticks. Of the 1000 sticks I make, shortest is 991mm and the tallest is 1009mm. That is within accepted tolerance for this product. That lets me estimate the SD as 18/6 = 3mm. Here we talking 3σ process. How does six sigma apply to the above situation? What will be the changes to σ, μ and range, and why ±1.5σ shift in mean is acceptable? Last edited by Samurai : 3rd April 2018 at 11:00. 
2nd April 2018, 19:50  #64  
TeamBHP Support  Re: Are you Six Sigma certified? Quote:
If this process become six sigma compliant, the new σ = Range/9 or 18/9 = 2mm. Since μ can deviate by ±1.5, the mean could vary from 997 to 1003. Then 997  3σ = 997  6 = 991mm 1003 + 3σ = 1003 + 6 = 1009mm The range remain the same, Mean (μ) can vary between 997 to 1003, and SD (σ) changes from 3mm to 2mm. Defect rates change from 0.27% to 0.00034%. This is the effect of moving a process from 3σ process to six sigma process. Does this make sense?  
3rd April 2018, 15:41  #65 
TeamBHP Support  Re: Are you Six Sigma certified? While I was waiting for green/black belts clarify my thoughts, I discussed this with another BHPian. He wondered why I assumed Range/6 = σ, and what is the meaning of mean shift by ±1.5σ. So I am further spitballing. In the walking stick example, I had mentioned that the lengths 991mm1009mm are limits of the tolerance, and that the shortest stick is 991mm and the longest stick is 1009mm for this sample. This is either perfect zero defect or near zero defect scenario. But taking the worst case scenario, what process comes closest? 1σ Process: At least 31% walking sticks will be outside of 9911009mm range. So this can't be it. 2σ Process: At least 4.5% walking sticks will be outside of 9911009mm range. So this can't be it either. 3σ Process: Only 0.27% walking sticks will be outside of 9911009mm. So this could be the worst σ value we could consider. That is why I assumed 3σ process, and got σ = Range/6, or 18/6 = 3mm. But there is one major problem with 3σ process, it has no tolerance for mean shift. As long as the mean is at 1000mm, everything is fine. However, after some wear and tear, the machine might shift the mean away from 1000mm. What if it starts making sticks of mean length of 1002mm, while the σ remains at 3mm. The ±3σ range now shifts to 993mm1011mm. The 3σ deviation on the higher end is now outside of specified tolerance. The six sigma allows for ±1.5σ deviation in the mean value itself. That means the machine can shift the mean from 1.5 times σ in either direction. But that is not possible while keeping σ at 3mm. At 3mm, the mean can shift from 995.5mm to 1004.5mm, if you add another 9mm (3x3mm) for 3σ deviation, we are looking at 986.5mm to 1013.5mm. Too many rejections. If the machine is replaced or improvised to provide σ = 2mm, then the ±1.5σ mean shift will be between 997mm1003mm. The 3σ deviation will be 6mm (3x2mm) in either direction, restricting the extremes to 991mm1009mm. While the range has remained same, due to decreased σ, the probability of sticks falling outside of tolerance range would have gone from 0.27% to 0.00034%. PS: What happens if distribution is not normal? Is six sigma still applicable? Last edited by Samurai : 3rd April 2018 at 16:07. 
4th April 2018, 01:25  #66 
BHPian Join Date: Sep 2006 Location: Delhi
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 Re: Are you Six Sigma certified? Step 1  I believe you need to start with the mathematical fundamentals first, understand how standard deviation or Sigma is defined and how it is relates to the mean. While you have derieved a way of finding out the acceptable standard deviation for a process to remain within spec, it is by no means a way to calculate the standard deviation of a sample or a population. Please find the relevant mathematical concepts explained here http://davidmlane.com/hyperstat/A16252.html http://www.dummies.com/careers/proje...forsixsigma/ Step 2  it is important to understand that a six sigma process is one in which the distance between the mean and a spec limit ( higher or lower ) is six standard deviations. Hence the probability of the proces producing something that it is out of spec is quite low, i.e, 199.9999998% Here 99.9999998% is the percentage of process outputs or values that will fall within the mean and six standard deviations, as compared to 99.7 % within three standard deviations or sigma. Explained in more detail here http://www.howardgitlow.com/definitionsofsixsigma.htm Hope this helps. 
4th April 2018, 01:47  #67  
TeamBHP Support  Re: Are you Six Sigma certified? Quote:
Quote:
My understand of six sigma is ±3σ or 3 standard deviation from mean in either direction, while allowing for 1.5σ shift of mean in either direction. That gives 3.4 defects per million.  
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