Glossary

# Sigma

Tags: Glossary

A Greek letter (Σ) commonly used to designate the standard deviation of a population, sigma is a statistical term that measures how much a process varies from perfection based on the number of defects per million units produced. In a process audit measurement, sigma would be the number of times the process failed for each million times the process was run. In either case, the subject is generally referred to as an 'opportunity.

## What is Sigma?

Sigma, denoted by the Greek letter Σ, is a statistical term that is commonly used to represent the standard deviation of a population. While this may sound complex, sigma is actually a simple concept that measures how much a process deviates from perfection based on the number of defects per million units produced.

To understand sigma, let's consider a manufacturing process. Imagine a factory that produces a million units of a product. Now, during the production process, there may be some defects or errors that occur. These defects could be anything from a faulty component to a mistake in assembly.

Sigma helps us quantify the level of defects in a process. In a process audit measurement, sigma would be the number of times the process failed for every million times the process was run. For example, if a process failed 10 times out of a million, the sigma value would be 10.

The sigma value provides us with a measure of the process's performance. The higher the sigma value, the better the process is performing. A higher sigma value indicates that the process has fewer defects and is closer to perfection.

Sigma is often referred to as the number of defects per million opportunities. An opportunity refers to a chance for a defect to occur. For example, if a product has 10 components, each component represents an opportunity for a defect. So, if there are a million units produced and each unit has 10 components, there would be a total of 10 million opportunities.

By calculating the number of defects per million opportunities, we can determine the sigma value and assess the process's performance. This allows us to identify areas for improvement and implement measures to reduce defects and increase efficiency.

In summary, sigma is a statistical term that measures how much a process deviates from perfection based on the number of defects per million units produced. It provides us with a quantitative measure of a process's performance and helps us identify areas for improvement. By striving for higher sigma values, organizations can enhance their efficiency and deliver higher quality products or services.