GE is arguably one of the best examples of Six Sigma excellence today. An often heard phrase is, “Motorola invented Six Sigma and GE perfected it.”A slick “variation weapon” GE has developed is called Span. I have never worked for GE but have worked with many former GE employees who have been kind enough to fill me in on this variation busting tool.
What is Span?
Span is another measure of dispersion much like the range. When calculating the range we simply take the difference between the largest data point and smallest data point. When dealing with non normal data using the range is likely safer than using the standard deviation. Read here for an explanation on why this is.
With Span we have another option for dealing with this non normal data, and let’s face it, much of the data out there is non normal. The secret to Span is that it ignores extreme outliers which can sometimes mislead us and instead looks at the difference between the 95th percentile and 5th percentile of the data set.
Specifically, Span is calculated as follows: 95th percentile – 5th percentile
Where can we use Span?
GE uses Span for things like focusing in on how well they are doing with on time delivery performance. There is an excellent article on iSixSigma about Span. In it you will hear from people like the former 80/20 man himself, Jack Welch, comment on how GE uses Span to focus in on their customers. You can access the article here.
If you have any real life experience using Span please do share.