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Beginners Guide to Six Sigma

What's a Sigma?

Sigma is a letter within the Greek alphabet. Among other uses, the lower case of the sigma () is used to signify the sandard deviation. Standard deviation is a statistical term that is used to identify the range between difference members of a population from the mean or average.

To simplify figuring out the standard deviation, let's say we have a person who is 40 years old and we have a person who is 50 years old. The average age would be 45. The standard deviation would be 5 - the 40 year old is five years away from the mean and so is the 50 year old.

Why Six?

In the example above with two people, ages 40 and 50, the population has a standard deviation of one. That means that everyone in the population group is one standard deviation from the average. This is a very small population and not realistic in the real world. In the real world, populations are quite large and not as easy to define. In the real world, most populations have data points within 1, 2, 3, 4, 5 and six standard deviations.

In statistics, about 68% of a population should fall within one standard deviation of the mean. 95% of the population should fall within 2 standard deviations of the mean. The six in six sigma means that 99.99999980268% of the population being measured should fall within six standard deviations from the mean.

This is assuming a normal population - one that is not highly skewed in one direction or another. Using the previous example of the 40 and 50 year old, suppose that we added more people to the group. However, we added six more 50 year olds. This would be a skewed population. Normal populations would be if we added six more individuals evenly spaced between 40 and 50 year old.

Six Sigma as a tool

Six Sigma is a tool that is used primarily in manufacturing organizations to ensure that products being produced are of the highest quality. The goal is to strive for no more than 3.4 defects per million products produced. Defects are usually considered to be caused by variances in the process. For example - if one person makes a widget following 5 steps and another person makes the same widget by using only 3 steps (omitting 2 steps), then there is a process variance which could lead to defects.

In order to implement Six Sigma, data must be captured, analyzed and variances in processes must be identified. Once variances are identified, plans must be made and implemented to reduce the variances in the process and control the processes in the future. This will reduce defects and produce higher quality products.

Conclusion

Six Sigma is a highly disciplined methodology. When implemented successfully, this methodology has helped corporatons save millions of dollars and provide higher quality products to consumers.

Learning More
http://www.isixsigma.com/s ixsigma/six_sigma.asp
http://ww w.ge.com/en/company/companyinf o/quality/whatis.htm
http://www .sei.cmu.edu/str/descriptions/ sigma6_body.html
http://en.wiki pedia.org/wiki/Standard_deviat ion

Learn more about this author, Linda J Banks.
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