Variation Reduction

All processes have variation; it is a natural outcome of mechanical and human behaviour. Customer dissatisfaction is created when variation in a process causes the spread of outputs (the voice of the process) to exceed that which the customer expects and is prepared to tolerate (the voice of the customer) . The Six Sigma project aims to reduce variation (as measured by standard deviation termed s ) so that the probability is very low that an output will fall outside the customer requirement. The more consistent and ‘on target’ the process, the more satisfied customers will be.
To put a scale on the sigma levels most processes operate at around three sigma or 67,000 defects per million opportunities for a defect to be counted (e.g. one misspelled word every other line of text). A Six Sigma process would operate at around three defects per million opportunities (e.g. one misspelled word in a 450 page book) .