Sigma’s lineage dates back to the Greeks. It is the 18th Greek letter used to designate a standard deviation, but many of you probably already knew that. As a business term, sigma can measure the capability of any given process to perform defect-free work. The higher the sigma value, the less likely a process will produce defects.

So, a company working at two sigma makes over 50,000 mistakes per million opportunities. Not exactly something you’d brag about. A company that operates at 3.8 sigma is getting it right 99.9966 percent of the time. Pretty good, eh? Sure, in the vast picture of things. But what is that remaining percent? Looking at other industries, it is equal to 5,000 botched surgical procedures every week, four accidents per day at major airports, 200,000 wrong drug prescriptions each year. How good does it look now?