You'll need to look at the context to know whether they're talking about the quality methodology or whether they are actually referencing six standard deviations away from the mean. When using this simple model, the standard deviation (sigma) is equal to (optimistic - pessimistic) / 6. The beta distribution PERT formula is: duration = (optimistic + pessimitic + 4*most likely) / 6 WIth respect to the PERT task duration, the beta distribution version of the formula basically is taking your date estimates and forcing them onto a simple probability function that looks like a bell curve. It's just a shorthand way of referencing their goal of defects being at a rate comparable with one in a million. That is where the name Six Sigma comes from. If you look at a normal distribution (a bell curve), to achieve a probability at such a low level you need to go approximately six standard deviations away from the mean. The goal was to achieve a rate of approximagtely one defect per million items. The idea behind Six Sigma is that they wanted to drive their defect rate down to near zero. Other examples would be TQM (Total Quality Management), or ZD (Zero Defects). Think of it as just one more method in a family of quality managment approaches over they years. Generally when you hear "Six Simga" mentioned, it is as Cornelius says - it is a quality managmenet methodology. I think that you're keying in on the word "sigma" and that it is perhaps the cause of some confusion. I will change the text in that newsletter so we don't give the wrong impression. So you are absolutely correct in saying "six sigma" means six standard deviations above and below the mean. This means that 99.99% of your output is without defect.įor the PMP exam you have to know the statistical percentages for 1, 2, 3 and 6 sigma: For instance you might read that "Your process is performing to six sigma". The Six Sigma methodology has a strong focus on numbers, describes quantitatively how a process is performing and uses standard deviations (or sigma) from the mean as a measure. Six sigma as a measure of standard deviation: And a defect is defined as "nonconformity of a product or service to its specifications." Six Sigma at many organizations simply means a measure of quality that strives for near perfection. The idea was to improve processes by eliminating defects. Six Sigma is a disciplined, data-driven approach and methodology that was originally developed by Motorola. Here is a better explanation: Six Sigma as a methodology: And based on what you say we have achieve our goal.Īnd oh my! You are so right about what you noticed in that sentence from the newsletter. We try to make it interesting and educational. First of all I'm glad that you like our newsletter.
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