#2 sigma calculation how to#

If you’re striving for a 6 sigma process, you can see that this process, which is at a 0.83 process sigma, is far from achieving that goal. Defects are the total number of defects you counted in the 50 sample invoices. Opportunities are found by multiplying your sample of 50 times your 4 possible defects. While there are a number of tables available on the internet, here’s a simple calculator that will do it for you. Your DPMO value can also be converted to a sigma level value. If your organization does not produce a large volume of output, you can also calculate defects per thousand opportunities, or defects per hundred opportunities by multiplying by the appropriate number. To calculate DPMO, you would use this formula: The formula for that is:Īs an example, you could take a sample of 50 invoices, total the count of all defects found in those 50 invoices (assume a total of 150 defects), and then divide that number by your sample size of 50 to get an average estimate of 3 defects per unit or invoice. You can use the defect frequency to calculate something we call DPU, or defects per unit.

Both are defective, but certainly they are not wrong to the same degree. In our example, your invoice can have up to four different types of opportunities (for defects), which could then define your invoice as a defective invoice.Ī downside of using defectives as a measure, is that you can have an invoice with just a small spelling error in the address line, while another invoice might have an incorrect calculation, wrong address, and wrong customer name. We can then define a defective as an object that has one or more defects that may make the object unacceptable.

Each defect can cause a disruption and upset your customer. Each one is an opportunity to make a mistake on the invoice that you send to your customer. For example, an invoice may have a defect or error in the address line, invoiced amount, discount, or delivery date. There can be multiple flaws or defects in an object. A defect is a flaw or discrepancy in a process or object.

#2 sigma calculation how to#

In other words, although statistical tables indicate that 3.4 defects / million is achieved when 4.5 process standard deviations (Sigma) are between the mean and the closest specification limit, the target is raised to 6.0 standard deviations to accommodate adverse process shifts over time and still produce only 3.4 defects per million opportunities.If you’re curious as to what Defects Per Million Opportunities (DPMO) means, how to calculate it, what its benefits are, and how best to use it for understanding the performance of your process, read on. * The table assumes a 1.5 sigma shift because processes tend to exhibit instability of that magnitude over time.

The other side of the process distribution, which may have a tail beyond the farther specification, is ignored by the Cpk calculation. Note: the conversion of Sigma Level to Cpk is only an approximation because Cpk is based only upon the specification limit closest to the process mean. The 1.5 sigma shift may or may not be an accurate estimate of the actual long-term instability of your process. In essence, the 1.5 sigma shift indicates that if you intend to have 3 DPMO over the long term, the process must be more capable than the 4.5 sigma (Cpk) indicated by a normal curve in order to accommodate instability or process shifts that occur over time. By convention established at Motorola, where the Six Sigma program originated, the Sigma level is adjusted by 1.5 sigma to recognize the tendency of processes to shift over the long term. The following table lists Defects Per Million Opportunities with the corresponding Sigma Level.Īlso shown is a direct conversion to a Cpk level based on the area under a Normal Curve.