Six Sigma certification

Six sigma certification or concept will be explained here. This is the basics of six sigma certifications such as six sigma green belt and six sigma black belt. It also gives the answer to the question why a project is called a six sigma project?.

An example to understand six sigma concept

A customer wants a shaft with a diameter with the specifications, the lower specification limit(LSL) and upper specification limit (USL) as 24.5 cm and 27.5 cm respectively. That means customer will not accept the shaft if the diameter goes beyond 27.5 or lower than than 24.5. He will reject the shaft if it’s not in the specification.

To understand the concept of Six Sigma projects we want to know the following basics also.

The bell curve

Suppose we collected the dimensions of some samples of this shaft and made a graph with X axis as the diameter value and the Y axis as the frequency of the occurrence of the value. When we draw a curve including outer points of the graph, it will resemble like a bell curve, if it is a normal distribution. Here we will consider only normal distribution, because its best for understanding the basics. Also the centre portion of the curve will be the mean. Please refer the following graph.

Let ‘d’ be the standard deviation of this data set. Standard deviation is the measure of how long the data is spread from the mean value. If the standard deviation is high the spread is also high. If the standard deviation is low the spread will also be low.